Lower Prevalence of Celiac Disease and Gluten-Related Disorders in Persons Living in Southern vs Northern Latitudes of the United States

Background & Aims The association between prevalence of celiac disease and geographic region is incompletely understood, but the occurrence of several autoimmune disorders has been found to vary along a North−South gradient. We examined geographic, demographic, and clinical factors associated with prevalence of celiac disease and gluten-free diet in the United States. Methods In a population-based study, we analyzed data on gluten-related conditions from the National Health and Nutrition Examination Survey, from 2009 through 2014, on 22,277 participants 6 years and older. We identified persons with celiac disease based on results of serum tests for IgA against tissue transglutaminase and endomysium or on both a health care provider diagnosis and adherence to a gluten-free diet. Gluten avoidance without celiac disease was defined as adherence to a gluten-free diet without a diagnosis of celiac disease. We compared mean serum levels of biochemical and nutritional markers based on status of gluten-related conditions. Results We found 0.7% of participants to have celiac disease and 1.1% of participants to avoid gluten without celiac disease. Celiac disease was more common among individuals who lived at latitudes of 35°−39° North (odds ratio, 3.2; 95% confidence interval, 1.4−7.1) or at latitudes of 40° North or more (odds ratio, 5.4; 95% CI, 2.6−11.3) than individuals who lived at latitudes below 35° North, independent of race or ethnicity, socioeconomic status, and body mass index. Gluten avoidance without celiac disease was more common among individuals who lived at latitudes of 40° North or more, independent of demographic factors and body mass index. Participants with undiagnosed celiac disease (identified by positive results from serologic tests) had lower mean levels of vitamin B-12 and folate (data collected from 2009 through 2012) than persons without celiac disease. Participants with a health care provider diagnosis of celiac disease had a lower mean level of hemoglobin than persons without celiac disease. Mean levels of albumin, calcium, iron, ferritin, cholesterol, vitamin B-6, and vitamin D (data collected from 2009 through 2010) did not differ between participants with gluten-related conditions and those without. Conclusions In the US population, a higher proportion of persons living at latitudes of 35° North or greater have celiac disease or avoid gluten than persons living south of this latitude, independent of race or ethnicity, socioeconomic status, or body mass index. Mean levels of vitamin B-12 and folate are lower in individuals with undiagnosed celiac disease, and levels of hemoglobin are lower in participants with a diagnosis of celiac disease, compared with individuals without celiac disease.