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Lactose Intolerance in Adults: Biological Mechanism and Dietary Management

Yanyong deng, benjamin misselwitz.

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Author to whom correspondence should be addressed; E-Mail: [email protected] ; Tel.: +41-791934795.

Received 2015 Jul 14; Accepted 2015 Sep 14; Collection date 2015 Sep.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license ( http://creativecommons.org/licenses/by/4.0/ ).

Lactose intolerance related to primary or secondary lactase deficiency is characterized by abdominal pain and distension, borborygmi, flatus, and diarrhea induced by lactose in dairy products. The biological mechanism and lactose malabsorption is established and several investigations are available, including genetic, endoscopic and physiological tests. Lactose intolerance depends not only on the expression of lactase but also on the dose of lactose, intestinal flora, gastrointestinal motility, small intestinal bacterial overgrowth and sensitivity of the gastrointestinal tract to the generation of gas and other fermentation products of lactose digestion. Treatment of lactose intolerance can include lactose-reduced diet and enzyme replacement. This is effective if symptoms are only related to dairy products; however, lactose intolerance can be part of a wider intolerance to variably absorbed, fermentable oligo-, di-, monosaccharides and polyols (FODMAPs). This is present in at least half of patients with irritable bowel syndrome (IBS) and this group requires not only restriction of lactose intake but also a low FODMAP diet to improve gastrointestinal complaints. The long-term effects of a dairy-free, low FODMAPs diet on nutritional health and the fecal microbiome are not well defined. This review summarizes recent advances in our understanding of the genetic basis, biological mechanism, diagnosis and dietary management of lactose intolerance.

Keywords: lactose intolerance, lactase deficiency, lactose malabsorption, FODMAP, genetic test, hydrogen breath test, irritable bowel syndrome

1. Lactose and Lactase

Lactose is a disaccharide consisting of galactose bound to glucose and is of key importance in animal life as the main source of calories from milk of all mammals, all except the sea lion. Intestinal absorption of lactose requires hydrolysis to its component monosaccharides by the brush-border enzyme lactase. From week 8 of gestation, lactase activity can be detected at the mucosal surface in the human intestine. Activity increases until week 34 and lactase expression is at its peak by birth. The ability to digest lactose during the period of breast-feeding is essential to the health of the infant as demonstrated by congenital lactase deficiency that is fatal if not recognized very early after birth. However, following the first few months of life, lactase activity starts to decrease (lactase non-persistence). In most humans, this activity declines following weaning to undetectable levels as a consequence of the normal maturational down-regulation of lactase expression [ 1 ]. The exceptions to this rule are the descendants of populations that traditionally practice cattle domestication maintain the ability to digest milk and other dairy products into adulthood. The frequency of this “lactase persistence trait” is high in northern European populations (>90% in Scandinavia and Holland), decreases in frequency across southern Europe and the Middle East (~50% in Spain, Italy and pastoralist Arab populations) and is low in Asia and most of Africa (~1% in Chinese, ~5%–20% in West African agriculturalists); although it is common in pastoralist populations from Africa (~90% in Tutsi, ~50% in Fulani) [ 2 ].

2. Genetics of Lactase Persistence

Lactase persistence is thought to be related to the domestication of dairy cattle during the last 10,000 years. Lactase persistence is inherited as a dominant Mendelian trait [ 3 ]. Adult expression of the gene encoding lactase (LCT), located on 2q21 appears to be regulated by cis -acting elements [ 4 ]. A linkage disequilibrium (LD) and haplotype analysis of Finnish pedigrees identifies two single single nucleotide polymorphisms (SNPs) associated with the lactase persistence trait: C/T-13910 and G/A-22018, located ~14 kb and ~22 kb upstream of LCT, respectively, within introns 9 and 13 of the adjacent minichromosome maintenance 6 (MCM6) gene [ 3 ]. The T-13910 and A-22018 alleles are 100% and 97% associated with lactase persistence, respectively, in the Finnish study, and the T-13910 allele is ~86%–98% associated with lactase persistence in other European populations [ 5 , 6 , 7 ]. The genotype in China is C/C-13910, and no SNP associated with lactase persistence has been identified in the lactase gene regulatory sequence [ 8 , 9 ]. However, there are several lactase gene single nucleotide polymorphisms of this kind in other populations. Lactase persistence is mediated by G-13915 in Saudi Arabia [ 10 ], in African tribes by the G-14010, G-13915, and G-13907 polymorphism ( Figure 1 ) [ 11 , 12 ]. Thus, lactase persistence developed several times independently in human evolution in different areas of the world [ 11 ]. Multiple independent variants have allowed various human populations to quickly modify LCT expression and have been strongly conserved in adult milk-consuming populations, emphasizing the importance of regulatory mutations in recent human evolution [ 13 ]. In adult patients with homozygous lactase persistence, enzyme levels at the jejunal brush border are 10-times higher than for patients with homozygous non-persistence, and heterozygous individuals [ 14 ].

Map of the lactase (LCT) and minichromosome maintenance 6 (MCM6) gene region and location of genotyped single nucleotide polymorphisms (SNPs). ( a ) Distribution of 123 SNPs included in genotype analysis; ( b ) map of the LCT and MCM6 gene region; ( c ) map of the MCM6 gene; and ( d ) location of lactase persistence-associated SNPs within introns 9 and 13 of the MCM6 gene in African and European populations [ 12 ].

3. Biological Mechanism of Lactose Intolerance

About two thirds of the World’s population undergoes a genetically programmed decrease in lactase synthesis after weaning (primary lactase deficiency) [ 15 , 16 ]. Additionally, in individuals with lactase persistence the occurrence of gastrointestinal infection, inflammatory bowel disease, abdominal surgery and other health issues can also cause a decrease in lactase activity (secondary lactase deficiency). Both conditions must be distinguished from congenital lactase deficiency, which is an extremely rare disease of infancy with approximately 40 cases having been reported, mainly in Finland [ 2 ].

Whatever the cause, lactase deficiency results in unabsorbed lactose being present in the intestinal tract, which has effects that can lead to symptoms of lactose intolerance in susceptible individuals [ 17 ]. First, the increased osmotic load increases the intestinal water content. Second, lactose is readily fermented by the colonic microbiome leading to production of short chain fatty acids and gas (mainly hydrogen (H 2 ), carbon dioxide (CO 2 ), and methane (CH 4 )). These biological processes are present also for other poorly-absorbed, fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) that are ubiquitous in the diet [ 18 , 19 ]. Double-blind, cross-over studies in healthy volunteers applied scintigraphy or magnetic resonance imaging to document oro-cecal transit time together with breath testing to assess fermentation of the substrate. Fructose (a disaccharide similar to lactose) was seen to increase small bowel water, accelerate oro-caecal transit time (OCTT) and trigger a sharp increase in breath hydrogen production ( Figure 2 ), whereas 30 g glucose (a well-absorbed control) had no effect [ 20 , 21 ]. It should be noted that these effects are seen for poorly-absorbed, fermentable disaccharides both in health and in patients with gastrointestinal disease [ 22 , 23 , 24 ]. Long-chain carbohydrates (e.g., fructans, cellulose (“dietary fiber”)) that are not digested or absorbed by the small intestine have less impact on small bowel transit than short-chain carbohydrates; however, fermentation of this material in the large bowel produces similar effects on colonic function [ 21 ].

Small bowel water content (SBWC) and breath hydrogen (H2) concentrations after drinking each of the drinks: glucose and fructose. The time of drinking ( t = 0 min) is highlighted in the chart. Values of SBWC are mean volume (mL) ± s.e.m (standard error of mean). Values of H2 are mean concentration (p.p.m.) ± s.e.m. Figure modified from Murray et al . [ 21 ].

Malabsorption is a necessary precondition for lactose or FODMAP intolerance; however, the two are not synonymous and the causes of symptoms must be considered separately [ 25 ]. The threshold for dietary lactose tolerance is dependent on several factors including the dose consumed, residual lactase expression [ 2 ], ingestion with other dietary components [ 26 ], gut-transit time, small bowel bacterial overgrowth [ 22 , 23 ], and also composition of the enteric microbiome (e.g., high vs. low fermenters, hydrogen vs. methane producers) [ 25 , 27 , 28 , 29 ]. In addition to these environmental and physiological factors, it has been shown that patients with irritable bowel syndrome are at particular risk of both self-reporting dairy intolerance [ 9 , 30 ] and experiencing symptoms after lactose and FODMAP ingestion [ 31 , 32 ].

Symptoms of lactose intolerance generally do not occur until there is less than 50% of lactase activity. Regular lactose intake may also have an effect. Although lactase expression is not up-regulated by lactose ingestion, tolerance could be induced by adaptation of the intestinal flora [ 26 ]. Further, most people with lactase non-persistence can tolerate small amounts of lactose (less than 12 g, equivalent to one cup), especially when it is combined with other foods or spread throughout the day [ 26 , 33 ]. A double-blinded, randomized, three-way cross over comparison of lactose tolerance testing at 10 g, 20 g and 40 g lactose was performed in patients with diarrhea predominant irritable bowel syndrome (IBS-D) and controls in a Chinese population with lactase deficiency [ 31 ]. The study design included a dose below normal symptom threshold (10 g), plus a dose reflecting normal intake at a single meal (20 g) and a “positive control” such as that used in epidemiological trials (40 g). The multiple-dose method ( Figure 3 ) not only demonstrates the effect of dose in both study groups, but also guides nutritional management in a given patient. Importantly, the risk of symptoms in this study was greatly increased in IBS-D patients, especially at low-moderate doses found in the diet [ 31 ]. Indeed, few healthy controls with lactase non-persistence reported gastrointestinal (GI) symptoms except at the 40 g lactose dose [ 31 ]. IBS patients are known to be more sensitive to a variety of dietary and physical interventions that distend the GI tract [ 34 ]. Further studies in the same Chinese population demonstrated that anxiety, visceral hypersensitivity (defined by rectal barostat) and high-levels of gas production on breath tests are associated with patient reports of symptoms after ingestion of a modest (20 g) dose of lactose [ 35 ]. Heightened sensitivity to distension was associated with abdominal pain, bloating and overall symptom severity. Excessive gas production contributed to digestive symptoms, especially bloating and borborygmi [ 35 ]. Very interestingly, the same group of IBS patients that had lactose intolerance on hydrogen breath testing also had heightened activity of the innate mucosal immune system with increased counts of mast cells, intraepithelial lymphocytes and enterochrommafin cells in the terminal ileum and right colon ( Figure 4 ), with release of pro-inflammatory cytokines after lactose ingestion [ 36 ]. These observations are similar to those seen in patients with post-infective IBS and provide insight into the pathophysiological basis of food intolerance [ 37 ].

Prevalence of lactose malabsorption (LM) and lactose intolerance (LI) in patients with diarrhea predominant irritable bowel syndrome (IBS-D) and controls at 10-, 20-, and 40-g lactose hydrogen breath test (HBTs). * p < 0.05; ** p < 0.01 [ 31 ].

Representative photomicrographs showing tryptase positive mast cells (MCs) in the colonic mucosa of a healthy control (HCs) ( a – c ); an diarrhea predominant irritable bowel syndrome (IBS-D) patient with lactose malabsorption (LM) ( d – f ) and a patient with lactose intolerance (LI) ( g – i ). IBS-D patients with LI had increased mucosal MCs compared with LM and HCs [ 36 ].

Another condition that may play a role in food tolerance is small intestinal bacterial overgrowth (SIBO) caused by abnormally high bacterial counts in the small intestine, exceeding 10 5 organisms/mL [ 38 ]. SIBO is clinically characterized by bloating, abdominal discomfort and diarrhea, symptoms that are very comparable to those of lactose intolerance [ 39 ]. Bacterial fermentation of lactose with production of short-chain fatty acids and gas in the small bowel may be particularly likely to trigger abdominal symptoms. Consistent with this hypothesis, combined scintigraphy and breath test studies showed a higher prevalence of SIBO in IBS patients with lactose intolerance than in the lactose malabsorption control group [ 22 ]. This effect appeared to be independent of oro-caecal transit time and visceral sensitivity [ 22 ].

4. Clinical Diagnosis of Lactose Malabsorption and Intolerance

Problems with lactose absorption have been described, detected and diagnosed in several ways and this can lead to confusion among doctors and patients [ 26 ]. Lactase deficiency is defined as markedly reduced brush-border lactase activity relative to the activity observed in infants. Lactose malabsorption occurs when a substantial amount of lactose is not absorbed in the intestine. Because lactose malabsorption is nearly always attributable to lactase deficiency, the presence of this condition can be inferred from measurements of lactose malabsorption such as an increase of glucose in the blood or an increase of hydrogen in the breath. The term lactose intolerance is defined by patient reports of abdominal pain, bloating, borborygmi, and diarrhea induced by lactose. Less often it can present with nausea or constipation and a range of systemic symptoms, including headaches, fatigue, loss of concentration, muscle and joint pain, mouth ulcers, and urinary difficulties [ 40 , 41 ]; however, it is unclear whether these atypical symptoms are directly due to lactose ingestion, or related to the presence of so-called “functional diseases”, such as irritable bowel syndrome (IBS), which is often accompanied by multiple somatic complaints. Certainly, it is not possible to make a definitive diagnosis on clinical presentation alone because double-blind trials have shown that the association of self-reported lactose intolerance and the occurrence of symptoms after lactose ingestion are very poor [ 42 ], even in patients with lactase deficiency ( Figure 5 ) [ 9 ].

Lack of agreement between objective and subjective assessment of lactose intolerance [ 9 ].

There are various methods ( Table 1 ) for diagnosing lactose malabsorption and intolerance [ 25 ]. Testing of lactase activity in mucosal biopsies from the duodenum is regarded as the reference standard for primary and secondary lactase deficiency [ 43 ], however, limitations include the inhomogeneous expression of lactase [ 44 ] and the invasiveness of the test. Genetic tests may be useful for identifying lactase persistence in some European populations as the T-13910 allele is ~86%–98% associated with lactase persistence in European populations [ 5 , 6 , 7 ], however other SNPs are present in Arabian and African populations [ 10 , 11 , 12 ]. Future genetic tests will likely cover a range of genetic polymorphisms, potentially eliminating this limitation. A further limitation of both biopsy and genetic tests is that no assessment of symptoms is made. This impacts on the clinical relevance of these investigations because, as addressed above, only a proportion of patients with lactase deficiency develop abdominal symptoms after ingesting lactose [ 31 ].

Summary of tests for lactose malabsorption and lactose tolerance [ 25 ].

Lactose digestion and the association of maldigestion with symptoms can be assessed by the H 2 -breath test [ 45 ] and the lactose tolerance test [ 46 ]; however, the former is confounded by fluctuations of postprandial blood sugar. The H 2 -breath test can be false positive in the presence of small intestinal bacterial overgrowth; however, a larger problem is false-negative tests due to the presence of hydrogen non-producing bacteria in the colon (2%–43%) [ 17 ]. This problem of “hydrogen non-production” can be mitigated to some extent by examining patient reports of symptoms after the test dose. Patients with “false positive” breath tests complain of symptoms directly after ingestion. Those with “true positive” lactose intolerance complain of symptoms only after the substrate has entered the colon (usually 50–100 min). Another possibility is to combine the biopsy or genetic test (in Caucasians) with the H 2 -breath test; however, this is an expensive and time-consuming approach.

5. Treatment of Lactose Intolerance

Treatment of lactose intolerance should not be primarily aimed at reducing malabsorption but rather at improving gastrointestinal symptoms. Restriction of lactose intake is recommended because in blinded studies patients with self-reported lactose intolerance, even those with IBS, can ingest at least 12 g lactose without experiencing symptoms [ 26 , 47 ]. Even larger doses (15 to 18 g lactose) appear to be tolerated when dairy products are taken with other nutrients [ 26 ]. One retrospective case review reported improvement of abdominal discomfort, with lactose restriction in up to 85% of IBS patients with lactose malabsorption [ 48 ]; however, prospective studies show that lactose restriction alone is not sufficient for effective symptom relief in functional GI disease [ 49 ]. In our experience this approach is effective if symptoms are related only to dairy products; however, in IBS patients, lactose intolerance tends to be part of a wider intolerance to poorly absorbed, fermentable oligo-, di-, monosaccharides and polyols (FODMAPs) [ 9 , 30 ]. Evidence from recent trials indicates that this is present in about half of patients with IBS and this group requires not only restriction of lactose intake, but also a low FODMAP diet to improve gastrointestinal complaints. An initial controlled trial of a diet low in FODMAPs reported symptom improvement in 86% of IBS patients, compared to 49% for a standard dietary intervention [ 50 ]. Three randomized controlled trials have confirmed that a low FODMAP diet can benefit a wide range of symptoms in IBS patients [ 32 , 51 , 52 ]. All these studies included lactose restriction in the early “strict” phase of the dietary intervention; however, the specific role of lactose in causing symptoms was not assessed. A major issue with almost all dietary intervention trials is that the contribution of individual components (e.g. lactose) is difficult to assess as other dietary components (e.g., fat [ 53 ]) can also produce symptoms and, potentially, confound results.

Lactase enzyme replacement is another important approach in patients with “isolated” lactose intolerance that wish to enjoy dairy products. One double-blind, placebo-controlled, crossover study shows that in lactose malabsorbers with intolerance, lactase obtained from Kluyveromyces lactis represents a valid therapeutic strategy, with objective and subjective efficacy and without side effects [ 54 ]. Exogenous lactase obtained from Aspergillus oryzae or from Kluyveromyces lactis breaks down lactose into glucose and galactose to allow an efficient absorption [ 55 ].

A related strategy involves probiotics that alter the intestinal flora and may have beneficial effects in IBS patients [ 56 ]. Four-week consumption of a probiotic combination of Lactobacillus casei Shirota and Bifidobacterium breve Yakult improved symptoms and decreased hydrogen production in lactose intolerant patients. These effects appeared to persist for at least three months after suspension of probiotic consumption [ 56 ]. However, in another study, milk containing Lactobacillus acidophilus did not consistently reduce gastrointestinal symptoms in patients with self-reported lactose intolerance compared with control participants [ 26 ]. Further studies are required to provide high quality evidence to support or compare the efficacy of these strategies.

6. Long-Term Effects of Lactose or FODMAP Restriction

Although restricting dietary lactose or FODMAPs may improve gastrointestinal complaints, long-term effects of a diet free of dairy or FODMAPs products may be of concern [ 57 ]. Dairy products are the major source of calcium in many individuals. No study has addressed the safety and effectiveness of calcium replacement for patients with lactose intolerance; however, it seems reasonable to recommend increasing calcium intake from other foods or supplements in patients that restrict intake of dairy products, especially in the presence of other risk factors for osteoporosis.

Diet also has effects on the colonic microbiome. Altering the dietary intake of FODMAPs alter gastrointestinal microbiota [ 58 ] and a significant decrease in the concentration of probiotic bifidobacteria after four weeks of a low FODMAP diet has been reported [ 52 ]. Whether this change has any long-term implications is unknown. Recommending alternative foods is a key component of patient education and even with dietetic advice nutrient intake, in particular of calcium, can be compromised on a low lactose, low FODMAP diet.

Another issue that should be considered is the negative effect of dietary restriction on quality of life [ 9 , 59 ]. Patients with self-reported lactose intolerance restrict intake not only of dairy products but also of other foodstuffs due to general concerns about diet and health [ 9 , 59 ]. This is stressful and can be expensive as shown by the recent trend to “gluten free diets” [ 60 ]. Moreover, if not properly supervised, multiple food restrictions could lead to mal- or under-nutrition. Formal dietary intervention excludes a wide range of potential dietary triggers for a short period to achieve symptom improvement, followed by gradual food reintroduction to identify items and threshold doses that can be tolerated by patients.

7. Conclusions

Primary lactase deficiency can be regarded as the commonest “genetic disease” in the World, although, in truth, loss of lactase expression in adulthood represents the normal “wild-type” and lactase persistence the abnormal “mutant” state. Additionally, in secondary lactase deficiency, the ability to digest lactose can be lost due to infection, surgery and other insults. Whatever the cause, lactose malabsorption causes symptoms by several mechanisms: unabsorbed lactose leads to osmotic diarrhea; products of its bacterial digestion lead to secretory diarrhea and gas can distend the colon. Diagnosis of lactose malabsorption is based on detection either of the genetic mutation, loss of lactase activity in the enteric mucosa or evidence of malabsorption in the blood or breath. However, the presence of lactose malabsorption does not necessarily imply that abdominal symptoms are related to this process. The majority of healthy individuals with lactase deficiency tolerate up to 20 g lactose without difficulty. Instead, diagnosis of lactose intolerance requires concurrent assessment of lactose digestion and abdominal symptoms.

Recent studies have provided important new insight into the complex relationship between lactase deficiency, lactose malabsorption and symptom generation. This work has shed light on the wider issue of food intolerance as a cause of symptoms in irritable bowel syndrome and related conditions. Understanding the biological mechanism for food intolerance to lactose and FODMAPs will help clinicians make a definitive diagnosis and guide rational dietary and medical management. Ongoing studies will provide high quality evidence to document the efficacy and long-term effects of these strategies.

Acknowledgments

We thank Hua Chu for her excellent work in the Sino–Swiss trials referred to in this article. We acknowledge funding from Nestlé International that supported the Sino-Swiss trials into lactose intolerance and digestive health.

Author Contributions

Yanyong Deng and Benjamin Misselwitz researched and drafted the manuscript. Ning Dai and Mark Fox led many of the studies cited in this article, contributed to the draft manuscript and approved the final publication. All authors discussed and revised all drafts and approved the final manuscript.

Conflict of Interest

Ning Dai and Mark Fox have received research funding from Nestlé International for studies of lactose intolerance. Other authors have no relevant conflicts of interest to declare.

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StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

StatPearls [Internet].

Lactose intolerance.

Talia F. Malik ; Kiran K. Panuganti .

Affiliations

Last Update: April 17, 2023 .

Continuing Education Activity

Lactose intolerance is a clinical syndrome that manifests with characteristic signs and symptoms upon consuming food substances containing lactose, a disaccharide. Normally upon lactose consumption, it is hydrolyzed into glucose and galactose by the lactase enzyme, which is found in the small intestinal brush border. Deficiency of lactase due to primary or secondary causes results in clinical symptoms. This activity describes the pathophysiology of lactose intolerance and highlights the role of the interprofessional team in its management.

Review the pathophysiology of lactose intolerance.
Describe the presentation of a patient with lactose intolerance.
Summarize the management options for lactose intolerance.
Outline the importance of improving care coordination among interprofessional team members to improve outcomes for patients affected by lactose intolerance.
Introduction

Lactose intolerance is a clinical syndrome that manifests with characteristic signs and symptoms upon consuming food substances containing lactose, a disaccharide. Normally upon lactose consumption, it is hydrolyzed into glucose and galactose by the lactase enzyme, which is found in the small intestinal brush border. [1] Deficiency of lactase due to primary or secondary causes results in clinical symptoms. Disease severity varies among individuals. Lactose is present in dairy, milk products, and mammalian milk. [2] It is also sometimes referred to as lactose malabsorption.

Lactase deficiency is the commonest type of disaccharidase deficiency. Enzyme levels are at the peak shortly after birth and decline after that, despite continued lactose intake. Among the animal world, nonhuman mammals generally lose their ability to digest lactose into its components as they reach adulthood. Certain populations of the human species, such as those of South American, Asian, and African descent, tend to develop lactase deficiency. On the contrary, people of northern Europe origin or northwestern India usually retain the ability to digest lactose into adulthood. [3]

Lactose intolerance presents with abdominal bloating and pain, loose stools, nausea, flatulence, and borborygmi. [4] [5] Many people start avoiding milk as soon as a diagnosis is made, or even the suggestion of lactose intolerance is put forward. This leads to consuming specially prepared products with digestive aids, adding to the health care burden.

Lactase enzyme deficiency can occur in individuals with lower levels of this enzyme, resulting in failure to hydrolyze lactose into absorbable glucose and galactose components. There are four leading causes of lactase deficiency.

Primary Lactase Deficiency

It is the most common cause of lactase deficiency, also known as lactase non-persistence. There is a gradual decline in lactase enzyme activity with increasing age. Enzyme activity begins to decline in infancy, and symptoms manifest in adolescence or early adulthood. More recently, it has been observed that lactase non-persistence is of the ancestral form (normal Mendelian inheritance), and lactase persistence is secondary to mutation. [6] [7] [8]

Secondary Lactase Deficiency

Due to several infectious, inflammatory, or other diseases, injury to intestinal mucosa can cause secondary lactase deficiency. [9] Common causes include:

Gastroenteritis
Celiac disease
Crohn disease
Ulcerative colitis
Chemotherapy
Antibiotics

Congenital Lactase Deficiency

There is a decrease or absence of lactase enzyme activity since birth due to autosomal recessive inheritance. [10] [11] It manifests in the newborn after ingestion of milk. It is a rare cause of the deficiency, and its genetics are not very well known. [12]

Developmental Lactase Deficiency

It is seen in premature infants born at 28 to 37 weeks of gestation. [13] The infant's intestine is underdeveloped, resulting in an inability to hydrolyze lactose. This condition improves with increasing age due to the maturation of the intestine, which results in adequate lactase activity.

Epidemiology

Lactose intolerance is a common disease; however, it is rare in children younger than 5. It is most often seen in adolescents and young adults. On average, 65% of the world's population is lactose intolerant. [14] The prevalence of lactose intolerance is variable among different ethnicities. It is most common in African Americans, Hispanics/Latinos, and Asians and least prevalent in people of European descent. [15] Ethnic groups with a higher prevalence of lactose intolerance also are more likely to have lactose non-persistence. [16] [17]

The primary form is the commonest (found in up to 70% of the world's population, but not all of them are symptomatic). [18] [19] [20] On the contrary, the congenital type is extremely rare (with around 40 cases reported worldwide to date). [6]

In the US, the primary disease is much more common in certain ethnicities, such as African-Americans, American Indians, Hispanics or Latinos, and Asian-Americans, than in White Americans. [21] [22] [23] [24] [21] North Americans, Australians, and White Northern Europeans have the lowest rates, ranging between 2% and 15%. [21] [22] On the contrary, the prevalence of lactose intolerance is 50% to 80% in South Americans, around 100% in American Indians and some East Asians, and around 60% to 80% in Ashkenazi Jews and Africans. [21] [23] [24]

The age-related decline in lactase activity is generally complete during childhood; however, the decline has also been seen to occur later, in adolescence, particularly in Whites. [25] The eventual level and the duration of loss of lactase expression vary considerably per ethnicity. Chinese and Japanese people lose between 80% and 90% of activity within three to four years after weaning. Jews and Asians lose 60% to 70% over many years after weaning, and for White Northern Europeans and North Americans, it could take between 18 and 20 years for lactase expression to reach its lowest levels. [18] A low prevalence of lactase non-persistence is noted in patients of mixed ethnicity, whereas an increased prevalence is observed in the native ethnic group.

The onset of the disease is generally subtle and progressive in primary illness, and many patients first experience symptoms of intolerance in late adolescence and adulthood. [2] [3] As opposed to White Northern Europeans, Australians, and North Americans, earlier presentation is noted in Native Americans, Asian-Americans, African-Americans, and Hispanics/Latinos. [21] The secondary disease is commoner in children, particularly in developing countries where infections are a common cause. [9]

The sexes are affected equally.

Pathophysiology

The lactase enzyme is located in the brush border of the small intestinal mucosa. Deficiency of lactase results in the presence of unabsorbed lactose within the bowel. This results in an influx of fluid into the bowel lumen resulting in osmotic diarrhea. Colonic bacteria ferment the unabsorbed lactose-producing gas (hydrogen, carbon dioxide, and methane), which hydrolyzes lactose into monosaccharides. [26] This results in an additional influx of fluid within the lumen. The overall effect of these mechanisms results in various abdominal signs and symptoms.

An association has been reported between certain single nucleotide polymorphisms with lactose tolerance in a northeastern Brazilian population. In Indo-Europe, lactose intolerance is linked with rs4982235 SNP (or -13910C>T). [27]

Histopathology

In lactose intolerance, microscopic findings of the small intestine vary depending on the cause of lactase deficiency. In primary lactase deficiency, the mucosa appears normal. Lactase activity can be measured to assess the severity of the disease. The mucosa may be abnormal in secondary lactase deficiency, depending upon the underlying cause. It helps determine the secondary causes of the disease, such as celiac disease. Biopsy results may be normal if the mucosal abnormality is focal or patchy. [28]

History and Physical

Signs and symptoms of lactose intolerance manifest 30 minutes to 1 to 2 hours after ingesting milk (dairy) products. The severity of symptoms depends upon the amount of lactose consumed, the residual lactase function, and the small bowel transit time. [29] Common signs and symptoms may include the following:

Abdominal bloating
Abdominal Pain
Nausea and vomiting
Flatulence [30] [31]

Less commonly, it can present with headache, muscle pain, joint pain, mouth ulcers, urinary symptoms, and loss of concentration. [32] [33]

Lactose intolerance is evaluated by getting a careful history, performing a physical exam, and medical tests.

It is essential to take a past medical, family, and dietary history to determine the cause of lactose intolerance and exclude secondary causes.

Physical Exam

Assess for the presence of abdominal bloating, tenderness, and pain.

Medical Tests

Hydrogen breath test: This test measures the hydrogen content of breath after lactose ingestion. The test is positive for lactose malabsorption if the post-lactose breath hydrogen value rises >20 ppm compared with the baseline. [34]
Stool acidity test: Unabsorbed lactose is fermented by colonic bacteria into lactic acid, which lowers the stool pH.
Dietary elimination: One way to assess the underlying illness is to eliminate lactose-containing food products, which would result in the resolution of symptoms. Resumption of symptoms with the reintroduction of these products will indicate lactose intolerance. [35]
Milk tolerance test: Administer 500 mL of milk and obtain the blood glucose level. A rise in blood sugar of less than 9 mg/dL shows lactose malabsorption. [36]
Lactose tolerance test: This test determines lactose absorption after ingestion of a lactose-containing liquid. Measure serial blood glucose levels after giving an oral lactose load. After obtaining a fasting serum glucose level, 50 g of lactose is administered. [34] Serum glucose level is then measured at 0, 60, and 120 minutes. Failure of blood glucose levels to rise by 20 g may indicate lactose intolerance. This test has a specificity of 96% and a sensitivity of 75%. False-negative results may occur in patients with diabetes or small bowel bacterial overgrowth. The results are also affected by abnormal gastrointestinal emptying. [37]
Small bowel biopsy: This test is rarely performed as it is invasive. It is only indicated to rule out secondary causes of lactose intolerance.
Genotyping: It is an emerging test with higher sensitivity and specificity. It has been used in Germany and the Nordic states, but it is yet not widely available or practiced elsewhere. [38]
Treatment / Management

Management of lactose intolerance consists of dietary modification, lactase supplementation, and treating an underlying condition in people with secondary lactase deficiency.

Dietary Modification

Lactase-containing milk products and calcium supplements are recommended. Limiting the dietary intake of lactose by avoiding the intake of lactose-containing products improves the symptoms of the disease. The following products contain lactose and, therefore, must be avoided:

Soft and processed cheese
Pancakes and waffles
Mashed potatoes
Custard and pudding

Yogurt contains varying amounts of lactose and may cause symptoms in some patients. Greek yogurt has the least. Yogurt culture microorganisms can produce β-galactosidase as part of their lactose utilization pathway. This may promote lactose digestion in vivo. [39] Plant-based milk alternatives are becoming more available; however, technological issues, palatability, and nutritional balance remain concerns. [40] [41] Probiotics have been observed to improve symptoms, such as the DDS-1 strain of Lactobacillus acidophilus. [42] [43] Calcium and vitamin D supplements should also be recommended. In patients with secondary lactase deficiency, treatment should be directed at the underlying cause. [44]

Lactase Supplements

Lactase enzyme supplements contain lactase which breaks down lactose in milk and milk-containing products. They are available as lactase enzyme tablets or drops.

Differential Diagnosis

Other conditions to be considered in the list of differential diagnoses of lactose intolerance include:

Irritable bowel syndrome
Tropical sprue
Cystic fibrosis
Inflammatory bowel disease
Diverticular disease
Intestinal Neoplasm or polyp
Excessive ingestion of laxatives
Viral gastroenteritis
Bacterial infection
Pertinent Studies and Ongoing Trials

Emerging treatments include the following:

Fungal Beta-galactosidases

Two fungal beta-galactosidases from Aspergillus carbonarius ATCC6276 are beta-gal 1 and beta-gal 2. They can be given alone or in combination and may be used as an enzyme supplement for lactose intolerance. [45] Unlike current commercialized supplemental lactases, these purified enzymes demonstrate significant stability on exposure to simulated gastric conditions.

Nutrigenomics

Nutrigenomics may be used in the future management of hypolactasia through prompt identification of specific mutations or haplotype patterns that modulate dietary responses in affected individuals. [46]

Lactose intolerance has an excellent prognosis. Most patients have a considerable improvement in signs and symptoms with dietary modification alone. Lactose intolerant may lead to osteopenia. [47] [48] [49] Vitamin D deficiency is linked to the LCT -13910C>T gene variant of lactose intolerance among Whites. [49]

Complications

Following are some common complications:

Osteoporosis [15]
Malnutrition
Weight loss
Growth failure
Consultations

Once a diagnosis of lactose intolerance is made, consultation should be made with a gastroenterologist and dietician.

Deterrence and Patient Education

Lactose-intolerant patients and their families should be advised that ingestion of lactose-containing products generally only leads to reversible symptoms without causing permanent damage to the gastrointestinal tract (unlike celiac disease). Also, there are no long-term complications if an adequate intake of proteins, calories, calcium, and vitamin D is ensured. [21]

Primary and congenital lactase deficiency can not be prevented. However, secondary lactase deficiency could be prevented if underlying secondary causes are diagnosed early and promptly instituted appropriate treatment to preserve intestinal mucosal integrity. In addition, avoiding lactose-containing foods helps limit long-term disease severity.

Pearls and Other Issues

To avoid their use, people with lactose intolerance can check the ingredients on food labels for lactose on food products.

Some people with lactose intolerance can tolerate some milk and milk-containing products and may not need to avoid them completely.

Lactose intolerance is commonly confused with milk allergy. Lactose intolerance is a gastrointestinal disorder, while milk allergy is an autoimmune reaction against specific milk proteins. Milk allergy is life-threatening and presents early in infancy, while Lactose intolerance usually presents in adolescence or early adulthood.

Milk is rich in calcium and vitamin D. Prolong avoidance of milk in people with lactose intolerance can result in calcium and vitamin D deficiency.

Enhancing Healthcare Team Outcomes

The diagnosis and management of lactose intolerance are with an interprofessional team that includes a nurse practitioner, primary care provider, pediatrician, gastroenterologist, and an allergist. Lactose intolerance is commonly confused with milk allergy. Lactose intolerance is a gastrointestinal disorder, while milk allergy is an autoimmune reaction against certain milk proteins. Milk allergy is life-threatening and presents early in infancy, while Lactose intolerance usually presents in adolescence or early adulthood. It is important to educate the patient that they should always check the ingredients on food labels for lactose on food products to avoid their use when they have lactose intolerance. However, some people with lactose intolerance can tolerate some milk and milk-containing products and may not need to avoid them completely. Prolonged avoidance of milk in people with lactose intolerance can result in calcium and vitamin D deficiency. [50] [level 5]

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Disclosure: Talia Malik declares no relevant financial relationships with ineligible companies.

Disclosure: Kiran Panuganti declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

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A New Approach to the Study of Tolerance: Conceptualizing and Measuring Acceptance, Respect, and Appreciation of Difference

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Published: 09 September 2019
Volume 147 , pages 897–919, ( 2020 )

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Mikael Hjerm ORCID: orcid.org/0000-0003-4203-5394 1 ,
Maureen A. Eger ORCID: orcid.org/0000-0001-9023-7316 1 ,
Andrea Bohman ORCID: orcid.org/0000-0001-8335-9235 1 &
Filip Fors Connolly 1

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Previous empirical research on tolerance suffers from a number of shortcomings, the most serious being the conceptual and operational conflation of (in)tolerance and prejudice. We design research to remedy this. First, we contribute to the literature by advancing research that distinguishes analytically between the two phenomena. We conceptualize tolerance as a value orientation towards difference. This definition—which is abstract and does not capture attitudes towards specific out-groups, ideas, or behaviors—allows for the analysis of tolerance within and between societies. Second, we improve the measurement of tolerance by developing survey items that are consistent with this conceptualization. We administer two surveys, one national (Sweden) and one cross-national (Australia, Denmark, Great Britain, Sweden, and the United States). Results from structural equation models show that tolerance is best understood as a three-dimensional concept, which includes acceptance of, respect for, and appreciation of difference. Analyses show that measures of tolerance have metric invariance across countries, and additional tests demonstrate convergent and discriminant validity. We also assess tolerance’s relationship to prejudice and find that only an appreciation of difference has the potential to reduce prejudice. We conclude that it is not only possible to measure tolerance in a way that is distinct from prejudice but also necessary if we are to understand the causes and consequences of tolerance.

The Different Faces of Social Tolerance: Conceptualizing and Measuring Respect and Coexistence Tolerance

The Refined Theory of Basic Values

Worldwide divergence of values

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1 Introduction

Tolerance is generally understood as a necessary component of a functioning democracy and stable world order. Indeed, the Preamble of the United Nations Charter (UN 1945 ) declares the intention of its member states “to practice tolerance and live together in peace with one another as good neighbours.” Later, the United Nations Educational, Scientific and Cultural Organization (UNESCO 1995 ) clarified the meaning of tolerance. According to Article 1.1., “[t]olerance is respect, acceptance and appreciation of the rich diversity of our world’s cultures, our forms of expression and ways of being human…Tolerance is harmony in difference.”

Tolerance is often invoked as something to which individuals and societies should aspire, especially given diversity, in all its forms, is increasingly a feature of contemporary democracies. When tensions arise, some leaders call for a “greater tolerance” of particular groups or encourage general efforts to become “a more tolerant society.” For example, in 2004, then Secretary-General of the UN, Kofi Annan said, “Tolerance, inter-cultural dialogue and respect for diversity are more essential than ever in a world where peoples are becoming more and more closely interconnected” (United Nations 2004 ). According to UNESCO Director-General Audrey Azoulay, “Tolerance is an act of humanity, which we must nurture and enact each in our own lives every day, to rejoice in the diversity that makes us strong and the values that bring us together” (UNESCO 1996 ). Yet, what does this mean in practice? That those who hold prejudicial attitudes should fight against their dislike of particular out-groups? That everyone should respect others’ values or attitudes even when they are contrary to their own? That society should always value or embrace diversity? Leaders rarely give answers to these questions. Unfortunately, science does not provide much guidance either.

Over 40 years ago, Ferrar ( 1976 :63) proclaimed, “The concept of tolerance is in a state of disarray.” According to Ferrar, tolerance has multiple dimensions, but the empirically oriented literature primarily emphasizes one: negative attitudes towards out-groups. She argues that when scholars rely on indicators of prejudice towards social groups or discrimination in their analyses of tolerance, they imply that “tolerance and its opposite are sufficiently described by reference to categoric prejudgments of minority groups and their members” (p. 67). We take this argument one step further and contend that incorporating prejudice into the meaning or measurement of tolerance makes the concept of tolerance analytically indistinguishable from prejudice, confusing what tolerance is and how it differs from dislike, disapproval, or disgust with specific out-groups. Despite a great deal of empirical research on tolerance over the past 40 years, some of which includes overt efforts to clarify the concept, this disarray persists. We claim that the central problem continues to be the conflation—explicit or implicit—of prejudice and (in)tolerance, either in conceptualization or operationalization.

Despite problems in the scientific literature, it is generally accepted that tolerance is something necessary for democracies. As Kuklinski et al. ( 1991 :3) note: “Few aspects of political life so directly and immediately touch upon the daily lives of common citizens as does their tolerance toward each other.” Footnote 1 To answer some of the pressing, if not existential questions facing multiethnic, democratic societies today, we need a clearer understanding of tolerance—what it is and what it isn’t. And, before we can begin to assess its impact on various aspects of social, economic, and political life, we need better tools to measure it.

In the sections that follow, we begin with a review of previous empirical research on tolerance. Then, based on scholarship on toleration, we advance a conceptualization of tolerance that is abstract as well as analytically separate from other concepts. Specifically, we define tolerance as a value orientation towards difference . Next, we develop new measures to operationalize three aspects of tolerance. Importantly, these measures do not include references to specific social or political out-groups or particular types of attitudes or behaviors. Instead, the items capture acceptance of, respect for, and appreciation of difference in the abstract. We administer a survey twice—first using a random sample of the Swedish population and second using an online format in Australia, Denmark, Sweden, United Kingdom, and the United States. After validating our measures empirically, we demonstrate their relationship to prejudice and other variables. We conclude with a discussion of our results, their contributions, limitations, as well as practical implications.

2 Previous Approaches to the Study of Tolerance

In general, two broad conceptualizations of tolerance exist. The first approach understands tolerance as a permissive attitude towards a disliked out-group. Thus, this conceptualization begins with the notion that in order to be tolerant one first has to be prejudiced. Previous research from this tradition incorporates the dislike of out-groups into the measurement of tolerance. We critique this approach on both theoretical and methodological grounds. The second approach defines tolerance as a positive response to diversity itself. This conceptualization is analytically distinct from prejudice and lays the foundation for superior operationalization. However, previous studies that begin with this definition have nevertheless relied on measures of prejudice in their analyses, which means our understanding of tolerance remains limited. Thus, our critique of this approach is primarily methodological. In the sections that follow, we examine these approaches to tolerance in greater detail and discuss their theoretical and empirical implications.

2.1 Tolerance as Phenomenon Dependent on Prejudice

The first conceptualization of tolerance can be summarized as: Person X is tolerant if Person X dislikes Person Y doing Z. Person X has the means to prevent Person Y from doing Z, but Person X refrains from doing so. Therefore, in order to tolerate someone or something, one first needs to experience disapproval or dislike, and then despite these negative sentiments exhibit permissiveness or acceptance. Tolerance in this sense implies “forbearance” or the readiness to “put up with” with what one dislikes (Rapp and Freitag 2015 ; Robinson et al. 2001 ; Sullivan et al. 1979 ; Verkuyten and Slooter 2007 ).

To “put up with” in political terms translates into allowing the expression of objectionable ideas (Sullivan et al. 1979 ), or more specifically, to extend social rights related to political participation and freedom of speech to groups one dislikes or disagrees with (Mondak and Sanders 2005 ; Rapp 2017 ). The “objection criteria” is at the core of this conceptualization, as “… one cannot tolerate ideas of which one approves (Gibson 2006 , p. 22).” Tolerance, in this sense, is a sequential or twofold concept (Rapp and Freitag 2015 ), where the crux of the matter is the initial position of like or dislike.

This understanding of tolerance is theoretically problematic for two reasons. First, by this definition, the existence of tolerance depends on the existence of prejudice. People who are not prejudiced are incapable of being tolerant let alone becoming more tolerant. Moreover, we can only gauge if society has become more tolerant by knowing if a society has become less prejudiced. Second, this definition excludes reactions to the mere existence of out-groups. In theory, an individual must have the capacity to prevent what is disliked in order to demonstrate tolerance. Because the presence of racial and ethnic out-groups is likely beyond any one person’s control, it becomes theoretically impossible to be tolerant of this type of diversity. Beyond these theoretical shortcomings, we also argue that this understanding of tolerance necessarily leads to the empirical conflation of tolerance and prejudice.

Many empirical studies of tolerance begin with the assumption that particular groups are widely disliked or, at the very least, viewed with skepticism (Bobo and Licari 1989 ; van Doorn 2016 ; Gibson and Bingham 1982 ; Gibson 1998 ). An important example is Stouffer’s ( 1955 ) seminal work on tolerating non-conformity (e.g., socialism and atheism) in the United States. In his study, examples of tolerance include the willingness to extend rights such as freedom of speech to these “non-conformist” groups. Verkuyten and Slooter ( 2007 ) study tolerance of Muslim beliefs and practices among Dutch teenagers. They motivate their choice of out-group with reference to the general status of Islam in Dutch society. The main issue with this “unpopular groups” strategy is that it is impossible to distinguish empirically between people who support rights for groups they dislike and people who support rights because they are positively disposed towards the group in question (Sullivan et al. 1979 ).

Sullivan et al. ( 1979 ) introduce the “least-liked” approach in part to avoid contaminating the measurement of tolerance with respondents’ attitudes towards specific groups. As they put it: “If we had merely asked all respondents whether communists should be allowed to hold public office, their responses would depend not only on their levels of tolerance, but also on their feelings toward communists” (p. 785). To establish initial dislike, Sullivan et al. ( 1979 ) measure respondents’ attitudes about various groups in society. After identifying a disliked, or least liked, group, the respondents report preferences regarding these group members’ participation in political and civic activities. Adopting the same strategy, Rapp ( 2017 ) first examines respondents’ attitudes towards groups that are ethnically, religiously, or culturally diverse from them. Anti-immigrant attitudes constitute the rejection component. She then restricts her sample only to those respondents who are prejudiced, because theoretically, they are the only ones who can be tolerant.

We argue that neither strategy truly captures tolerance, because in both prejudice remains fundamental to the measurement of tolerance. Footnote 2 Thus, regardless of whether dislike is assumed, as in the unpopular group strategy, or measured, as in the least liked approach, empirical findings actually reflect respondents’ attitudes towards an out-group.

In summary, this first approach to the study of tolerance treats prejudice as a prerequisite for tolerance. Footnote 3 If dislike of an out-group is a precondition for tolerance, this means that in theory one cannot be tolerant without having been prejudiced at some earlier point in time. Conceptually there is a great deal of overlap between prejudice and tolerance, which inevitably extends to the measurement of tolerance (e.g., Kuklinski et al. 1991 ; Davis 1995 ; Gibson 1998 ; Verkuyten and Slooter 2007 ; Rapp and Ackermann 2016 ).

2.2 Tolerance as a Phenomenon Distinct from Prejudice

A second approach to analyzing tolerance does not begin with dislike of groups and instead focuses on subjective reactions to the existence of diverse values, behaviors, and lifestyles. Kirchner et al. ( 2011 :205) define tolerance as “the willingness to tolerate or accept persons or certain groups as well as their underlying values and behavior by means of a co-existence (even if they are completely different from one’s own).” Norris ( 2002 :158) defines tolerance as “the willingness to live and let live, to tolerate diverse lifestyles and political perspectives.” Dunn et al. ( 2009 :284) define tolerance “as a non-negative general orientation toward groups outside of one’s own.”

Some scholars make explicit that tolerance does not require prejudice. For example, Allport ( 1958 :398) points out while tolerance may mean putting up with something or someone one dislikes, such as a headache or a neighbor, “the term also has a more rugged meaning. We say that an individual who is on friendly terms with all sorts of people is a tolerant person. He makes no distinction of race, color, or creed. He not only endures but, in general, approves his fellow men.” By providing two examples of tolerance—one where the subject dislikes what he tolerates and one where he likes what he tolerates—Allport ( 1958 ) demonstrates not only that dislike is not fundamental to tolerance but also that it is unnecessary for tolerance. Chong ( 1994 :26) also argues that, based on this conception, is it is possible to tolerate things that we like. Thus, tolerance may be either to endure something or to show esteem for something.

As they do not begin with disliking a group of people, these definitions are more analytically distinct from prejudice. They emphasize reactions to diversity without specifically identifying marginalized social groups or indicating that individuals’ behaviors, values, or lifestyles are anything other than different from one’s own. However, some of these conceptualizations of tolerance incorporate the word tolerate or intolerance into its own definition. Moreover, some definitions equate acceptance with tolerance while others treat acceptance and tolerance as two different things. We maintain that while these definitions are more analytically distinct from the previous approach, they still lack conceptual clarity.

Nevertheless, previous research from this tradition has failed to operationalize tolerance in a manner consistent with its own definition. Put simply, these studies also incorporate prejudice into their measurement of tolerance. Persell et al. ( 2001 ) rely on five questions to measure tolerance. Two ask about attitudes towards homosexuals and three refer to African–Americans. Both Dunn et al. ( 2009 ) and Kirchner et al. ( 2011 ) use a long battery of measures found in the World Values Survey (WVS) to capture respondents’ willingness to have individuals from specific social groups as neighbors. These groups span from people of a different race to heavy drinkers to people with a criminal record. Kirchner et al. ( 2011 ) argue that by focusing on a multitude of groups, they are able to distinguish between individuals who tolerate only one “objectionable” group from those who tolerate many or all. While this approach does improve upon studies that analyze attitudes towards a few, specific groups, it still measures attitudes towards out-groups. In fact, according to Norris ( 2002 :158), this WVS scale “taps many of the most common types of narrow-mindedness and bigotry” (also cited in Kirchner et al. 2011 :205), put simply, prejudice.

Our critique of this strand of research is methodological. By incorporating prejudice into the measurement of tolerance, these previous studies do not analyze attitudes about the existence of diversity nor do they investigate an “orientation toward groups outside of one’s own” (Dunn et al. 2009 :284). Instead, they measure a willingness to accept specific groups as neighbors, which certainly speaks to how respondents feel about these groups and not diversity in general. Measuring attitudes towards a multitude of groups does not change this; these indices only tell us the extent to which one is prejudiced—in other words, if one is prejudiced towards one, two, or many, but always a subsample of out-groups. In summary, this conceptualization defines tolerance as a phenomenon distinct from prejudice and emphasizes reactions to diversity in all forms. However, previous research from this tradition has not measured tolerance in a way that is consistent with that definition.

2.3 Other Concerns: Abstraction and Multidimensionality

We have argued that incorporating elements of prejudice into the meaning and measurement of tolerance has rendered intolerance and prejudice conceptually and empirically indistinguishable. Yet there are other limitations to these two approaches that stem from a lack of abstraction. First, using attitudes about specific values, behaviors, lifestyles or social groups as indicators of tolerance makes it difficult to study tolerance longitudinally. The status of particular social groups changes over time due to a number of factors, including societal prejudice. Norms about what is acceptable to do, say, or believe also change. Linking tolerance to something specific means we can only measure whether positive or negative attitudes towards a specific entity have changed over time.

Second, by focusing on attitudes towards particular social or political groups, previous research has often conflated conservative beliefs with intolerance and liberal attitudes with tolerance. Ferrar ( 1976 :75–76) identifies this problem as originating with Stouffer’s index ( 1955 ), which connects tolerance to permissive attitudes regarding civil liberties of groups associated with the political left but not political right. It is, of course, theoretically possible to have a principled commitment to diversity while simultaneously holding conservative beliefs about political issues, just as it is also possible to oppose specific types of diversity and take liberal political stances. Although more recent studies incorporate attitudes towards a greater number of social groups (Dunn et al. 2009 ; Kirchner et al. 2011 ), this bias still exists.

Third, scholars that focus on attitudes towards groups not only conflate prejudice with tolerance but also disregard people’s ability to support diversity in the abstract. Sniderman et al. ( 1989 :27) call this outright dismissal of principled tolerance a deeply cynical and pessimistic view of “the willingness of the average citizen to embrace, disinterestedly and consistently, a foundational value of democratic politics—tolerance.” We contend that at the very least this is an empirical question worthy of investigation. Without measures of tolerance in the abstract, we simply do not know.

Finally, most previous empirical research neglects the multidimensionality of tolerance, although theoretical research on tolerance emphasizes this. Thinking about tolerance as an attitude towards diversity, Walzer ( 1997 ) argues that there are five types of tolerance that vary from resigned acceptance to aesthetic endorsement. Similarly, Forst ( 2013 ) claims that there are four types of tolerance, which range from acceptance to appreciation. Persell et al. ( 2001 :208) contend that complete tolerance would entail recognition and acceptance while a lesser version would be “an unwillingness to openly express intolerance.” Despite definitions that include a number of ways that tolerance can be expressed, subsequent empirical analyses treat tolerance as a unidimensional concept (e.g., Kirchner et al. 2011 ).

In summary, previous studies of tolerance suffer from one or more of the following three main problems: (1) conceptual overlap of tolerance and prejudice; (2) operational overlap of tolerance and prejudice; and (3) a lack of abstraction in the conceptualization and operationalization of tolerance. Moreover, previous empirical research has, for the most part, ignored the multidimensionality of tolerance, something emphasized in theoretical work. Therefore, in the next section, we advance a conception of tolerance and develop new measures of tolerance consistent with our definition. To avoid the pitfalls of previous approaches, we do not identify particular social groups, behaviors, or values in our indicators. Further, our measures are politically and temporally neutral.

3 Tolerance as an Orientation Towards Difference

We advance a new conception of the phenomenon in question and define tolerance as a value orientation towards difference . The fundamental question is not whether one puts up with something disliked but how one responds to the existence of diversity itself. This definition is abstract and analytically distinct from other concepts. Footnote 4 Our focus is on subjective reactions to difference; thus, this conceptualization does not require dislike of or identification of potentially objectionable groups, ideas, or behaviors. In practice, this definition is consistent with the approach to tolerance that does incorporate forbearance into its definition.

Our definition—a value orientation towards difference—is consistent with Walzer’s ( 1997 ) understanding of tolerance as an attitude or state of mind. This conception of tolerance is also consistent with previous accounts that do not see prejudice as a prerequisite for tolerance (e.g., Allport 1958 ; Chong 1994 ; Walzer 1997 ) and suggest that multiple expressions of tolerance are possible (e.g., Persell et al. 2001 ; Rapp 2017 ). To identify different possible expressions of tolerance, we adapt Forst’s ( 2013 ) four dimensions. We choose these not because they differ substantively from others but instead because Forst draws distinctions among different types of tolerance in a manner that lends itself well to the empirical investigation of the phenomenon.

According to Forst ( 2017 ), there are four understandings of tolerance and each may be present in a society at the same time. The first and second are related in that they both understand tolerance as a permissive relationship between different groups. In this expression of tolerance, groups do not interfere with each other or their practices but instead accept their existence. The difference between the first and second conception is the structure of society. In the first conception, the groups have unequal power. There is a clear majority that tolerates a minority group. In the second version, the groups have roughly equal power. Because we do not want to distinguish theoretically between societies with different social structures and systems of stratification, we combine these two. Thus, we identify the most basic expression of tolerance as an acceptance of difference .

Forst maintains that tolerance may also be respect for diversity or esteem for diversity. In Forst’s third conception of tolerance, individuals show respect for diversity by viewing disparate groups as morally and politically equal even though they may differ fundamentally in beliefs, practices, and lifestyles. In his fourth conception, tolerance is esteem or appreciation for diversity. According to Forst, esteem is a more demanding reaction to diversity than respect. This version of tolerance means viewing others’ beliefs, practices, or lifestyles as something valuable and worthy of ethical esteem even though they are different from one’s own. Thus, we call the second and third expressions of tolerance respect for difference and appreciation of difference .

One can think of different aspects of tolerance as points on a continuum (Walzer 1997 ). One can also think of these expressions as hierarchical, where individuals who appreciate diversity are also likely to respect and accept diversity, yet acceptance of diversity does not necessarily mean one appreciates it. Our conception of tolerance has clear advantages in terms of measurement. By identifying three distinct aspects of tolerance, we can measure different expressions of tolerance instead of measuring the number of groups one dislikes. Indeed, because we do not identify particular social groups, behaviors, or values in our indicators, our measures are politically and temporally neutral. In the next section, we describe our tolerance measures as well as our survey design and data.

4 Data and Methods

4.1 samples and surveys.

We measure tolerance in two different samples. The first is a random sample of the Swedish population (aged 18 years and older). We administered the survey via the national postal service in spring of 2016. We sent the survey once without reminders. Our response rate is 27.6%, which generated a sample of 1107 individuals. The respondents are comparable to the general population in Sweden in regards to gender (49.7% women) and average age (50.9 years). People with higher education are slightly underrepresented in our sample. In 2016, 27% of the Swedish population had three or more years of tertiary education, while only 19% of our respondents above 25 years have at least 3 years of tertiary education. Footnote 5 11.1% of the sample is foreign-born, which is lower than the 17.9% of the total population born abroad in 2016, but not surprising given the survey was administered in Swedish.

In addition to questions about tolerance, our survey includes a number of questions associated with prejudice, such as attitudes towards immigrants and homosexuals. We include these so that we can assess whether our items capture something distinct from prejudice. These additional items come from established cross-national surveys and have been validated in previous empirical research. We also ask respondents about their political preferences and voting behavior. As previously mentioned, the survey also includes demographic questions.

To investigate if of our measures of tolerance have the same meaning in other countries, we rely on a second dataset, a cross-national sample of individuals from Australia, Denmark, Sweden, the United Kingdom, and the United States. Country selection is one of convenience, as we were invited to add our tolerance items to an existing Qualtrics web-survey Footnote 6 in each of the five countries. Our resulting dataset includes only questions about demographic background and tolerance. In total, there are 6300 respondents with equal numbers from each of the countries. To minimize potential carry-over effects for each item measuring tolerance, we randomized the item order for every respondent. Previous studies comparing population data and survey data provided by self-selected panels such as Qualtrics indicate that these samples are fairly representative (Heen et al. 2014 ). We report descriptives for the cross-national sample by country in “Appendix 1 ” section.

4.2 Measures of Tolerance

To develop our measures, we ran two pilot studies in 2014 and 2015 with self-selected samples. The first pilot study was online and the web address widely advertised. The second pilot study was a paper survey administered to university students. We included 15–20 tolerance items in each. We used these studies to get feedback about the wording of questions and run preliminary analyses. Preliminary results indicated that 9 items produced a good model fit in a SEM analysis, but given we did not use representative samples in the pilot studies, we still included 17 items in the final Swedish survey.

We administered our nationally representative paper and online surveys in 2016. Results from analyses of these samples corroborated preliminary results from the pilot studies. Therefore, we kept a total of 9 items, which as a result of further analyses became 8. Ultimately, we only retained items that adequately load on their respective factor (acceptance, respect, and appreciation) and do not have high cross-loadings on the other two factors. Some have argued that unidirectional scales risk acquiescence bias (e.g., McClendon 1991 ; Billiet and McClendon 2000 ), where differences among items are underestimated, producing a seemingly coherent scale. However, other research suggests this concern is overstated (Rammstedt and Farmer 2013 ). Research on bidirectional items reveal that this approach also has limitations, as items worded both positively and negatively may damage response accuracy (Schriesheim and Hill 1981 ). With these risks in mind, we settled on positively worded items and randomized the items in the cross-national survey. Table 1 reports the final selection of items we use to capture each of the three dimensions of tolerance.

Descriptive statistics for each measure are found in Table 2 . Responses vary from ‘completely disagree’ to ‘completely agree’ on a five-point Likert scale. Scores for each item indicate that on average respondents articulate moderate to fairly high levels of tolerance. Most items display modest skewness, which is expected given the mean values. However, this should be of little concern given the robustness of maximum likelihood estimators (e.g., Reinartz et al. 2009 ), normal distribution of the data, and that all variables are modestly skewed in the same direction. We report descriptive statistics for our cross-national sample in “Appendix 2 ” section.

We rely on these two datasets for a number of different analyses. First, we use our Swedish sample to test a three-factor model of tolerance. To do this we rely on a structural equation model (SEM). Next, we use our second sample and multi-group confirmatory factor analysis to validate our results cross-nationally. In our next set of analyses, we regress latent constructs of attitudes towards out-groups on tolerance. Last, we provide a demographic portrait of tolerance by examining levels of tolerance among different demographic groups in Sweden.

5.1 Factorial Structure of Tolerance

To test our proposed three-factor model of tolerance we conduct a confirmatory factor analysis. In Fig. 1 , we present standard overall model fit statistics, including Chi squared test, comparative fit index (CFI), Tucker-Lewis index (TLI), and the root mean squared error of approximation (RMSEA). CFI, TLI, and RMSEA all indicate a good model fit. The Chi squared for the model fit is significant, which is expected given the large sample size (N = 1077). In order to improve the model further, we specify a correlation between item Ac1 and Ac2 (CFI: 0.987, RMSEA: 0.042), which seems appropriate given the linguistic proximity of the items in question. However, we select the most parsimonious model since its model fit is clearly acceptable. Footnote 7

Structural equation model of tolerance, Swedish sample. Notes : Standardized correlations; CFI: 0.975 TLI: 0.959 RMSEA: 0.057 Chi square 76.388 (DF 17); N = 1083

Considering our three expressions of tolerance are correlated, it is possible that a one-factor model actually describes the data better or at least as well as the three-factor model. However, results indicate that this is not the case (CFI: 0.85, RMSEA: 0.13). We also ran analyses using a third item for respect (“It bothers me that some people have different traditions and lifestyles”) but its inclusion leads to slightly worse fit in the Swedish sample (CFI: 0.958, RMSEA: 0.068) and poor fit in the cross-national sample. Thus, we choose the most parsimonious 8-item model.

We only have two items measuring respect, which one could argue violates the common assumption that one needs three manifest items for a latent construct. However, this is not obvious as the contention exists that one item may suffice if the constructs are theoretically well defined (e.g., Bergkvist and Rossiter 2007 ; Hayduk and Littvay 2012 ). We also ran models where we set the covariance between the two respect items to zero (CFI = 0.975 RMSEA = 0.057) as well further restricting the model to include equal loadings. These alternative model specifications reduce the model fit marginally (CFI = 0.972 RMSEA = 0.058) but still indicate an acceptable fitting model. Additionally, we ran models with only two items for each dimension of tolerance, by removing Ac3 and Ap1 in a non-restricted model (CFI = 0.995 RMSEA = 0.034). Finally, we restricted this model, assigning the factor loadings to be pairwise equal while setting error term correlation between the pairwise variable to zero, producing a somewhat worse but still acceptable fit (CFI = 0.979 RMSEA = 0.063). Such models also yield standardized loadings between 0.68 and 0.85. This suggests (net further tests) that these six theoretically motivated variables may be used to measure tolerance in situations where it is pragmatic or necessary to have fewer items in a survey.

To assess if the model holds in different contexts, we use multi-group confirmatory factor analysis to test for measurement invariance across five countries (Australia, Denmark, Sweden, United Kingdom, and United States). These countries also represent three different languages (Danish, English, and Swedish). We report results from this analysis in Table 3 . According to Chen ( 2007 ), when N > 300 we should expect, foremost, CFI to decrease less than 0.01 between models. Results from the configural and the metric models demonstrate this. In fact, CFI is only reduced by 0.012 when comparing the metric and the scalar model, indicating that our invariance test almost reaches the threshold for scalar invariance. We choose to be conservative and only acknowledge metric invariance. Changes in RMSEA and SRMR are also within acceptable boundaries (Chen 2007 ).

Based on this analysis, we conclude that our respondents from Australia, Denmark, Sweden, the United Kingdom, and the United States understand tolerance similarly. Furthermore, we find support for metric invariance, meaning that the factor structure of the measure is equivalent across groups. This indicates that participants attribute the same meaning to the three latent constructs regardless of country. Thus, it is possible to study associations between three dimensions of tolerance and other individual-level variables across countries in the future. We conclude that the cross-national sample provides evidence that our measurement of tolerance works in three large countries in the English-speaking world as well as in two Northern European countries. The aim of this research is to advance a new way of operationalizing tolerance; thus, our efforts center on identifying commonalities across countries and not to explain differences between countries.

5.2 The Relationships Among Tolerance, Prejudice, and Other Attitudes

Results from our confirmatory factor analysis show that our measures of tolerance are internally consistent. Our next aim is to evaluate if these measures also have good convergent validity. We assess this by analyzing the bivariate relationship between tolerance and various measures of prejudice. We rely on measures commonly used in analyses of prejudice and already validated in previous research (e.g., Bohman and Hjerm 2016 ; Glick and Fiske 1996 ; Pettigrew and Meertens 1995 ). These variables capture prejudice, anti-gay sentiment, anti-immigration sentiment, and sexism. We expect the three aspects of tolerance to be associated with prejudice but to vary in the strength of those relationships. We also examine discriminant validity by analyzing the relationship between tolerance and attitudes towards welfare state support, as we have no theoretical reason to expect tolerance and welfare state attitudes to be related. These measures are also commonly used and empirically validated in previous research (e.g., Roosma et al. 2013 ; Eger and Breznau 2017 ). Table 4 describes the items included in these analyses.

Table 5 reports bivariate correlations among our three latent constructs of tolerance and these attitudes. Coefficients reveal a clear pattern: each aspect of tolerance is negatively correlated with prejudice, specifically negative attitudes towards immigrants, immigration, women, and homosexuals. As we move from acceptance of diversity to respect and appreciation, the size of the correlations increases. This indicates that people who express an appreciation for diversity are less prejudiced than those who only accept diversity. As expected, there are weak correlations among all aspects of tolerance and welfare state support.

Given the different expressions of tolerance are correlated, we also examine multivariate relationships to isolate their respective effects and to provide a clearer picture of the relationship between tolerance and prejudice. As Table 6 shows, when regressing the dependent variables on all three aspects of tolerance, only appreciation for diversity remains negatively associated with attitudes towards out-groups. These results show three important things. First, it is only appreciation of diversity—but not acceptance or respect—that helps explain prejudice. Thus, the bivariate relationships (reported in Table 5 ) between acceptance of diversity and prejudice as well as between respect for diversity and prejudice are driven by those who express all three types of tolerance. Second, these multivariate relationships demonstrate that it is possible to express some degree of tolerance regardless of whether one likes or dislikes racial and ethnic out-groups. Prejudice is not a prerequisite for acceptance of or respect for diversity. Third, it is possible to measure tolerance in a way that is distinct from prejudice towards specific out-groups.

We also note a relationship between acceptance of diversity and sexism. When controlling for different expressions of tolerance, this weak relationship becomes positive. As expected, we find no relationship between tolerance and welfare state support.

Although the three aspects of tolerance are correlated, additional analyses lead us to conclude that these results are not due to multicollinearity. First, we regress all outcome variables on factor scores to produce variance inflation factors (VIF), which indicate how much of the increased variance of a regression coefficient is due to collinearity. The VIF is approximately 1.5 or lower for all cases, indicating low levels of multicollinearity. Second, we compare the models reported in Table 6 with models where we set all (as well as combinations of) outcome variables on tolerance to be equal (see Marsh et al. 2004 ). This enables a test of Chi squared difference between models. In no case is the more restricted model better than the less restricted model (i.e., more freely estimated parameters), suggesting no multicollinearity issues.

5.3 Predicting Tolerance in Sweden

To provide a descriptive overview of tolerance in Sweden, we regress a number of demographic variables on these three tolerance constructs. For ease of interpretation, we use manifest tolerance scores instead of factor scores. Values to range from 1 to 5, with 5 indicating the highest level of each aspect of tolerance. In Table 7 , we report the relationships among tolerance and sex, age group, nativity, education level, civil status, subjective income and the Big Five personality traits. Results indicate no association between sex, nativity, or subjective income. Younger people express greater acceptance of, respect for, and appreciation for difference than those over 65 years old. Married and cohabitating partners articulate less acceptance than those who are single, but there are no differences in terms of respect and appreciation. Education matters for respect and appreciation but not for acceptance. In terms of personality, results show relationships among agreeableness and openness and all three dimensions of tolerance. Conscientiousness and neuroticism are weakly associated with one dimension. Extraversion is unrelated to tolerance.

Comparing these results to findings from the literature on prejudice, important differences emerge. Research on prejudice tends to show that women are less prejudiced than men; the elderly are more prejudiced than those who are younger; income is negatively associated with prejudice; and immigrants are much less prejudiced (towards other immigrants). Moreover, research consistently demonstrates that higher education is inversely related to prejudice. The results reported in Table 7 deviate from this pattern in that there is no sex difference nor any differences due to income or nativity. This provides further evidence that, although tolerance is related to prejudice, it is a distinct phenomenon. The relationships we find among tolerance and the Big Five personality traits are consistent with some studies of prejudice (e.g., Ekehammar and Akrami 2003 ) and inconsistent with others (Rapp and Freitag 2015 ).

6 Conclusion

In this article, we advance the study of tolerance by designing research to overcome both the theoretical and empirical conflation of prejudice and tolerance. There are two main theoretical approaches to tolerance. In the first, dislike of an out-group is a prerequisite for tolerance, meaning that one cannot be tolerant without having first been prejudiced. The implication of this conceptualization is that intolerance is also an indicator of prejudice, making it impossible to analytically—let alone empirically—separate the two constructs. According to the second theoretical tradition, tolerance is a phenomenon distinct from prejudice. Nevertheless, previous empirical research from this tradition incorporates prejudice into the measurement of tolerance by using questions that gauge attitudes towards specific out-groups. Our goal was to overcome these limitations by developing a theoretically driven, multidimensional conception of tolerance that can also be operationalized and measured in a way that is distinct from prejudice or any other concept.

Therefore, we began with a definition of tolerance that is analytically distinct from prejudice. We define tolerance as a value orientation towards difference . Based on previous theoretical work, we identified three expressions of tolerance: acceptance of, respect for, and appreciation of diversity. Next, we developed measures consistent with this conceptualization. Specifically, we designed survey items that capture reactions to diversity itself instead of attitudes towards specific out-groups, thereby also acknowledging people’s capacity for abstract thought. Our measures are temporally and politically neutral, which are essential for analyses over time and geography. With these efforts, we overcome additional limitations of previous research.

We administered two surveys, first in a single country (Sweden) and then cross-nationally in five countries (Australia, Denmark, Sweden, the United Kingdom, and the United States). Results from confirmatory factor analysis demonstrate that the three-factor model has good fit. Based on results from multi-group confirmatory factor analysis, we conclude that respondents across countries understand tolerance similarly. This means that these items can be used to examine tolerance, including its determinants or consequences, both within and across countries. Further, we demonstrated convergent validity by examining the relationship among tolerance and various measures of prejudice. We also found discriminant validity in relation to welfare attitudes. Relationships among types of tolerance and demographic variables lend credence to our claim that, although tolerance is correlated with prejudice, it is a distinct phenomenon that can, and should, be operationalized as such.

Our results suggest that only an appreciation of difference has the potential to reduce prejudice, but we do not know how tolerance is related to other individual-level or societal-level outcomes. Thus, we do not argue that individuals and societies should strive to appreciate all forms of difference. Future research should examine the extent to which these aspects of tolerance affect behavior—political and mundane. Research should also study the societal-level consequences of different aspects of tolerance.

Despite our contribution, we must acknowledge several limitations to our study. First, our data collection was limited to WEIRD countries (i.e., western, educated, industrialized, rich, and democratic) (Henrich et al. 2010 ); hence, future studies should assess whether our measures of tolerance are valid within other institutional and cultural contexts. Second, our empirical studies rely on cross-sectional data. Therefore, we do not know how stable our measures of tolerance are over time. Third, we have not examined our items in relation to earlier attempts at measuring tolerance, including political tolerance. This was beyond the scope of this paper, but something that future research should address.

Finally, we want to reiterate that our goal is not to make moral judgments about tolerance. The purpose of this research was to develop new measures that are consistent with an abstract, analytically distinct conceptualization of tolerance. Thus, we do not claim that tolerance is something inherently good or bad. The consequences of tolerance—different expressions and levels—remain empirical questions. Balint ( 2010 ) explains that “[e]ven if it is found empirically that learning about and respecting each other’s differences is useful for achieving and maintaining a tolerant society, crucially this does not give carte blanche to have this approach to difference maximized. It must be used in the minimal possible way to achieve its ends” (p. 137). Balint’s critique is consistent with Popper’s ( 1945 ) “paradox of tolerance.” Popper argues that tolerance of everything may actually lead to the disappearance of tolerance itself. Tolerating ideas or groups that infringe on others’ freedoms and civil rights may undermine their existence (both the groups and freedoms). Davis ( 1995 ) illustrates this point in his analysis of tolerance of the Ku Klux Klan (KKK) among African–Americans.

As stated at the outset of this research, we believe there is an important practical reason to clarify the meaning and measurement of tolerance, as it is often invoked as something important for individuals and societies to develop and demonstrate. In the face of increasing diversity across contemporary democracies, calls for “greater tolerance” of particular social groups has become commonplace. Yet without a clear understanding of tolerance, these imperatives are hollow. How much acceptance of, respect for, or appreciation of difference is necessary to reduce discrimination, violence, or other social problems that may undermine the functioning of democratic societies? We do not claim to have these answers, but by developing tools to study tolerance, this research moves us in the direction of being able to address these types of questions. Indeed, the analytical and methodological approach developed in this article makes this type of empirical research possible.

Although we acknowledge the relevance of tolerance for democratic societies, we make no moral arguments in this article. We do not claim that tolerance is something inherently positive or always good for society. Popper’s ( 1945 ) “paradox of tolerance” posits that unlimited tolerance actually leads to the disappearance of tolerance itself: “If we extend unlimited tolerance even to those who are intolerant, if we are not prepared to defend a tolerant society against the onslaught of the intolerant, then the tolerant will be destroyed, and tolerance with them” (p. 360). Rawls ( 1971 :220) also argues that just societies, when threatened, may prioritize self-preservation over tolerance for the intolerant.

Gibson ( 1992 ) tests Stouffer's “unpopular groups” versus Sullivan et al.'s “least liked” approach empirically. The analyses show no substantive difference between the two, which leads Gibson to conclude that “… there is clearly not a single “best” way to measure political intolerance” (p. 573). While we do not question Gibson’s empirical findings, we disagree with his conclusion.

Tolerance is also recurrent in research on prejudice, especially in analyses of attitudes towards immigrants and ethnic minorities. Here the use of tolerance is not necessarily theoretical, and intolerance and prejudice are generally regarded as equivalents. For example, Togeby ( 1998 ) uses tolerance interchangeably with broadminded views and (absence of) ethnocentrism, making an empirical distinction between positive attitudes towards immigrants coming to the country (prejudice) and positive attitudes towards immigrants already living in the country (tolerance). Other prejudice scholars conceive of tolerance constituting positive attitudes toward immigrants as well as by an abstract ideological belief in and endorsement of equality (Van Zalk et al. 2014 ; Miklikowska 2016 ). Hainmueller and Hiscox ( 2007 ), who study tolerance as a mediator of the education effect on immigration attitudes, operationalize tolerance by an “… array of different measures of individuals’ values and beliefs” (p. 429). The item most explicitly tied to tolerance captures views on laws against promoting racial or ethnic hatred, with more positive attitudes indicating greater tolerance.

Others researchers, however, explicitly describe tolerance as the absence of prejudice. Dunn and Singh ( 2011 ) define intolerance as “a negative general orientation toward groups outside of one’s own” (p. 319). The degree of tolerance is derived from the respondents’ willingness to accept as their neighbors social groups such as immigrants, drug users, homosexuals, or Jews. Evans ( 2002 ) focuses exclusively on racial prejudice and negative attitudes towards homosexuality, interpreting the absence of such attitudes as an expression of “focused tolerance.” For others, the equating of tolerance with positive out-group attitudes appears to come down to semantics. “Tolerance,” then, is not defined or operationalized, but only used to summarize positions on different indicators of prejudice (Crepaz and Damron 2009 ; Craig and Richeson 2014 ; Rustenbach 2010 ).

We call tolerance a value instead of an attitude because it is not a positive or negative evaluation of a specific object (Eagly and Chaiken 1998 ).

The slight underrepresentation of the highly educated differs from other surveys (like the ESS) where those with less education often are underrepresented. It is possible that this difference is due to survey mode or measurement of education level, which are not always perfectly comparable in cross-national designs.

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There are various rules of thumbs accounting for the magnitude of factor loadings. Hair et al. ( 1998 ) advocate for 0.6 whereas Stevens ( 1998 ) identifies 0.4 irrespective of sample size or purpose. Meanwhile, Tabachnick and Fidell ( 2007 ) suggest a very precise cut-off ranging from 0.32 to 0.71, where anything above 0.45 is considered fair. Hair et al. ( 2011 ) also argue that anything less than 0.4 should be dropped whereas 0.5 is moderate. They also claim that the average variance extracted (AVE) should be 0.5, which is the AVE for the first factor. So, even though items Ac3 and Ap1 contribute somewhat less to the latent factors we retain them in the model.

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Acknowledgements

Open access funding provided by Umea University. This research was presented at the 2018 Annual Meeting of the American Sociological Association. We thank Elizabeth Fussell, Debra Minkoff, and session participants for their comments and suggestions. We are also grateful to the participants of two pilot studies for their valuable feedback on survey items, as well as Anne-Marie Fors Connolly , Lena Hjerm, Jan Mewes, and Karen Snedker for volunteering their time stuffing envelops and to Erin Eger who also entered data. Finally, we thank anonymous peer reviewers for their useful comments and suggestions.

This research was supported by the Marianne and Marcus Wallenberg Foundation (Marianne och Marcus Wallenbergs Stiftelse [MMW]) Grant No. 2014.0019, the Swedish Foundation for Humanities and Social Sciences (Riksbankens Jubileumsfond [RJ]) Grant No. P14-0775:1, and the Swedish Research Council for Health, Working Life and Welfare (Forskningsrådet för hälsa, arbetsliv och välfärd [FORTE]) Grant No. 2016-07177.

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Hjerm, M., Eger, M.A., Bohman, A. et al. A New Approach to the Study of Tolerance: Conceptualizing and Measuring Acceptance, Respect, and Appreciation of Difference. Soc Indic Res 147 , 897–919 (2020). https://doi.org/10.1007/s11205-019-02176-y

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DOI : https://doi.org/10.1007/s11205-019-02176-y

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