By: Peter Olins, PhD on August 9, 2012.
In 2003, a landmark study was conducted to examine the prevalence of celiac disease (CD) in the US (Ref. 1), leading to the popularized number of “1 in 133″. However, this was an estimate, since it did not rely on a random sample of the US population (it did not address age, location, ethnic or social factors).
A study has just been published, describing the first ever analysis of the prevalence of celiac disease in a large, random sample of the US population (Ref. 2). The authors found a prevalence of 0.71%, corresponding to approximately 1.7 million people (in other words, 1 in 141). Only roughly one in six cases had been previously diagnosed, suggesting that there may be as many as 1.5 million people in the US who are not aware that they have the condition.
Several studies have investigated the prevalence of celiac disease in different countries. In the largest survey until now, involving people from Finland, Italy, Germany and the U.K., the prevalence of celiac disease ranged from about 0.3% in Germany to 2.4% in Finland (Ref. 3).
Past studies in the US have involved subsets of the US population, so a major question has remained: what is the prevalence in the population as a whole?
Ref. 1: Prevalence of Celiac Disease in At-risk and Not-at-risk Groups in the United States. Arch Int. Med. (2003) 163:286.
Fasano, A., et al.
Ref. 2: The Prevalence of Celiac Disease in the United States. Am J Gastroenterol (2012) doi:10.1038/ajg.2012.219 Rubio-Tapia, A., et al.
Ref. 3: The Prevalence of Celiac Disease in Europe: Results of a Centralized, International Mass Screening Project. Ann Med (2010) 42:587 Mustalahti, K., et al.
NHANES-Based Population Study
The current study (Ref. 2) relied on over 8000 individuals who were participating in the 2009-2010 National Health and Nutrition Examination Survey (NHANES), which was specifically designed to cover a statistically-relevant sample of the US population (Ref. 4).
NHANES is a multi-year series of studies designed to assess the health and nutritional status of adults and children in the United States. The survey is unique in that it combines interviews and physical examinations. The process involves an extensive questionnaire about health and lifestyle, plus the donation of a blood sample for future analysis. This results in a large set of information that can be analyzed at a later date in order to look for possible health trends.
The current celiac disease research survey was a collaboration between J. Murray, A. Rubio-Tapia, and T. Brantner (Mayo Clinic, USA), J. Ludvigsson (Orebro University Hospital and Karolinska Institute, Sweden) and J. Everhardt (National Institutes of Health, Bethesda, USA).
Ref. 4: NHANES Sampling Methodology http://www.cdc.gov/nchs/nhanes/nhanes2007-2008/sampling_0708.htm
Diagnosis of Celiac Disease
Blood was first analyzed for the presence of antibodies against tissue transglutaminase 2 (TG2), which is characteristic of untreated celiac disease. Positive samples were then tested for EMA (endomysial antibody) in order to confirm the presence of celiac disease. (While an intestinal biopsy is typically required for definitive celiac disease diagnosis, biopsy was not performed in this study, since the NHANES specifically does not involve invasive procedures). In addition to the celiac cases identified using the blood tests, 6 subjects who reported a previous CD diagnosis were also included in the final numbers. (Confirmatory blood tests were not required for these subjects, since antibody tests are typically negative for celiac patients on a gluten-free diet).
8814 subjects were selected, and 7798 met the criteria for the study. Subjects were at least 6 years of age, and had a median age of 45 years.
Forty-nine subjects showed a strong or weak response in the TG2 antibody test, and these were then tested using the EMA, resulting in a total of 30 confirmed cases. After including subjects who had a prior diagnosis, a total of 35 people were found to have celiac disease. After a statistical adjustment to account for the different groups present in the study, this corresponds to a prevalence of 0.71% in the United States.
Effect of Ethnicity on the Prevalence of Celiac Disease
Since celiac disease has a strong genetic component, it is likely that people from different ethnic backgrounds could have a different prevalence. The NHANES program separates subjects based on race or ethnicity. This involves rather subjective divisions based on skin color or national descent, so it does not directly address the true genetic background of the individual. Nevertheless, it was striking that the majority of CD cases identified (29 out of 35) were in the “white, non-Hispanic” category, with a prevalence of 1.01% in this group. The study did not involve a sufficient number of subjects in order to test the role of ethnicity in more detail.
Effect of Gender on Celiac Disease Prevalence
There was no significant gender difference in the prevalence values found. This is in contrast to the higher incidence rate that has been observed elsewhere for women. (“Prevalence” is a measure of the actual number of cases of a condition at a given time, while “incidence” refers to the rate of new diagnoses). In other words, in general medical practice, women are more likely to be diagnosed than men. The reason for the higher rate of diagnosis for women is not clear.
Estimate of the Number of People in the US on a Gluten-Free Diet
As part of the NHANES survey, subjects were asked if they were on a gluten-free diet. Fifty-five people reported that they were, although only 6 of these people had a prior diagnosis of celiac disease. Extrapolating from the 55 individuals to the general public, this corresponds to an overall “gluten-free diet prevalence” of 0.63%, or approximately 1.6 million people. This is the first time such a statistic has been obtained.
The study identified 29 cases of CD which had not previously been diagnosed, out of a total of 35. This means that about 5 out of six people have not yet been diagnosed, or about 1.5 million people in the US population! Clearly, this is a major public health issue, since untreated celiac disease can have major health consequences, some of which can be irreversible.
The effectiveness of diagnosis in Europe is much higher, perhaps because of the more proactive nature of their countrys’ health care systems, and includes active “case-finding” of family members of celiac patients (who are much more likely to have CD because of the strong role of genetics in the disease. Close relatives of celiacs have approximately a 10-20-fold increased risk of CD, while about 75% of identical twins share the condition.
- This is the first truly random sampling of the American population for the prevalence of celiac disease.
- A prevalence of about 0.71% was found, corresponding to about 1.7 million people in the US.
- The vast majority of cases of celiac disease (5 out of 6) go undiagnosed.
- CD prevalence is the same for males and females, but is higher in the “white, non-Hispanic” segment.
- About 1.6 million American report being on a gluten-free diet, most of them without having celiac disease.