Scandinavian Journal of Gastroenterology. 2013; 48: 921–925

ORIGINAL ARTICLE

Prevalence of gluten-free diet adherence among individuals withoutceliac disease in the USA: results from the Continuous National Healthand Nutrition Examination Survey 2009–2010

DANIEL V. DIGIACOMO1,2, CHRISTINA A. TENNYSON1, PETER H. GREEN1 &RYAN T. DEMMER2

1Department of Medicine, Celiac Disease Center at Columbia University, Columbia University, New York,NY 10032, USA, and 2Department of Epidemiology, Mailman School of Public Health, Columbia University,New York, NY 10032, USA

AbstractObjectives. Clinical inference suggests the prevalence of non-celiac gluten sensitivity is substantially higher than that ofceliac disease in the USA. Unfortunately, there are currently no data supporting these claims. The authors analyzednationally representative data to estimate the prevalence of adherence to a gluten-free diet among participants without celiacdisease and also to characterize the demographics and general health status of these participants. Study design andsetting. The Continuous National Health and Nutrition Examination Survey (NHANES) 2009–2010 enrolled 7762 indi-viduals representing the civilian, non-institutionalized, US population free of celiac disease. Participants responded tointerviewer administered questionnaires regarding current adherence to a gluten-free diet. Prevalence estimates werecomputed using SAS survey procedures. Results. There were 49 individuals who reported current adherence to a gluten-free diet reflecting a weighted prevalence of 0.548% (95% CI 0.206–0.889). The prevalence of a gluten-free diet was higherin females (0.58%) than males (0.37%), although this was not statistically significant (p = 0.34). Participants reporting agluten-free diet were older (46.6 vs. 40.5 years, p = 0.005), had higher high-density lipoprotein, lower iron and lower bodymass index. Conclusions. The estimated national prevalence of non-celiac gluten sensitivity is 0.548%, approximately halfthat of celiac disease. Future studies are merited in order to better understand the population burden of non-celiac glutensensitivity.

Key Words: Anti-endomysial antibody, anti-tissue transglutaminase antibody, celiac disease, gluten, gluten-free diet, glutensensitivity, NHANES

Introduction

Found in wheat, barley and rye [1], gluten is bothubiquitous in the US diet [2] and a necessary cause ofceliac disease, a systemic autoimmune disorder withan estimated prevalence approaching 1% in the USA[3–5]. Upon gluten ingestion, genetically predisposedindividuals experience an adaptive and innate immuneresponse resulting in intestinal inflammation andsubsequent villous atrophy [6].

Non-celiac gluten sensitivity is defined as a condi-tion manifested by “. . .one or more immunological,morphological or symptomatic alterations triggeredby gluten ingestion in individuals in whom celiacdisease has been excluded” [7]”. Symptoms mayinclude pain, bloating or fatigue [8,9]. The mecha-nism of symptom development in non-celiac glutensensitivity is unclear; although an innate immuneresponse to gluten in the intestine has been suggested[10]. The only treatment for non-celiac gluten

Correspondence: Ryan T. Demmer PhD, Department of Epidemiology, Mailman School of Public Health, Columbia University, 722W. 168th St, New York, NY10032, USA. Tel: +1 212 305 9339. Fax: +1 212 342 2756. E-mail: rtd2106@columbia.edu

(Received 24 April 2013; revised 15 May 2013; accepted 15 May 2013)

ISSN 0036-5521 print/ISSN 1502-7708 online � 2013 Informa HealthcareDOI: 10.3109/00365521.2013.809598

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sensitivity is a gluten-free diet. Despite an awarenessof gluten sensitivity among the general population[11], it is not recognized by many physicians and isregarded as a clinical “no man’s land” [12]”.Accordingly, market research has shown that themajority of those purchasing gluten-free foods arenot doing it under medical advice [13–15].The prevalence of individuals with non-celiac gluten

sensitivity in the USA is unknown and there arecurrently no diagnostic standards to define the con-dition. For the first time, there are nationallyrepresentative data through the National Health andNutrition Examination Survey (NHANES) on self-reported physician diagnosed celiac disease, gluten-free diet adherence and anti-tissue transglutaminase(tTg)/endomysial (EMA) antibody levels.The goal of this analysis is to estimate the

prevalence of adherence to a gluten-free diet (afterexclusion of celiac disease) as a surrogate marker fornon-celiac gluten sensitivity in the USA and charac-terize these individuals in terms of demographics andgeneral health status.

Methods

Sample

The Continuous NHANES is a complex, multistage,probability sample that is nationally representative ofcivilian, non-institutionalized persons in the USA.The current analysis utilizes the NHANES 2009–2010 cross-section. In 2009–2010, 7762 participantsreceived an in-person physical examination, serolog-ical testing for celiac disease and responded to acomprehensive set of health questionnaires. Celiacdisease exclusions (n = 35) were determined as des-cribed previously [16] by: i) a self-report physiciandiagnosis of celiac disease while on a gluten-freediet, ii) an tTg antibody value > 10.0 U/ml withcorresponding positive/slightly positive EMA antibody[17].The NHANES protocol was approved by the

National Center for Health Statistics institutionalreview board, and written informed consent wasobtained from all participants.Written parental consentwas obtained for participants < 18 years of age.

Gluten-free diet assessment and demographics

Adherence to a gluten-free diet was defined as anaffirmative answer to the following intervieweradministered question: “Are you on a gluten-freediet?” Interviewer administered health questionnairesassessed individual and family demographics includ-ing age (years), race/ethnicity (Mexican Hispanic,

Other Hispanic, non-Hispanic White, non-HispanicBlack, Other), gender (male/female), ratio of familyincome to poverty ranging from 0–4.99 and ‡5 (aspreviously defined [18]), smoking status (current vs.former/never) and educational level (yes vs. no highschool/general educational development (GED)completion).

Laboratory biomarkers

A standard biochemistry profile was obtained includ-ing: complete blood count with 5-part differential,hemoglobin, glycosylated hemoglobin (HbA1c), C-reactive protein (CRP), low-density lipoprotein(LDL)-cholesterol (Friedewald equation) [19] andhigh-density lipoprotein (HDL)-cholesterol. Irondeficient anemia was defined according to the WorldHealth Organization recommendations [20]. Usingthe American Heart Association guidelines, partici-pants were defined as having low (CRP <1.0 mg/l),medium (CRP 1–3 mg/l) or high (CRP >3.0 mg/l)risk for cardiovascular disease (CVD) [21].

Body and blood pressure measurements

Height, weight and waist circumference measure-ments were made according to standardized proto-cols. Body mass index (BMI) was calculated fromheight and weight. Participants > age 20 years werecategorized according to BMI levels as follows: BMI<18.00 kg/m2 = underweight, 18.50–24.99 kg/m2 =normal weight, ‡25.00 kg/m2 = overweight and‡30.00 kg/m2 = obese [22]. Participants aged 6–20 years were categorized according to BMI-for-agepercentile as follows: <5% = underweight, 5–84% = normal weight, 85–94% = overweight,‡95% = obese. Four blood pressure measurementswere taken and the average of the second and thirdwere used for analysis [23].

Statistical analysis

Survey procedures in SAS 9.2 were used to accountfor the complex sampling design and to estimateprevalence of adherence to a gluten-free diet. Partic-ipant characteristics were compared between partici-pants adhering or not adhering to a gluten-free dietusing categorical analyses for categorical variables(Rao-Scott modified chi-square) and ANOVA(F-test) for continuous variables.

Results

Participants had a weighted mean age of 40.6(95% confidence interval (CI) 39.6–41.6) years

922 D. V. DiGiacomo et al.

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and were 51.0% female, 66.2% White, 11.3%African American, 15.3% Hispanic and 7.16%Other race/ethnicity. The current sample is gener-alizable to 252,048,706 Americans aged 6–80 years.The absolute number of participants reporting a

gluten-free diet was 49, representing a weightednational prevalence estimate of 0.548% (95% CI0.205–0.889) or 1,380,381 (95% CI 517,930-2,242,849) individuals in the USA. The mean age ofparticipants adhering to a gluten-free diet was46.7 versus 40.5 years among participants who didnot report using a gluten-free diet (p = 0.005).Although not statistically significant, the prevalenceof a gluten-free diet increased greater than twofoldamong participants ‡39 years of age relative to indi-viduals <39 years (p = 0.07, Figure 1) and was alsohigher among females than males: 0.65% (95% CI0.154–1.14) and 0.44% (95% CI 0.143–0.744),respectively. The gender differential was more pro-nounced among participants ‡65 years of age(Figure 2). The prevalence of gluten-free diet amongHispanics, non-Hispanic Blacks, non-Hispanic Whitesand Other race/ethnicity were 0.44% (95% CI 0.068–

0.814), 0.83% (95% CI 0.175–1.48), 0.44% (95% CI0.012–0.874) and 1.29% (95% CI 0.00–2.72), res-pectively (p for any difference = 0.33) and there wasno difference in the mean family income to povertyratio among individuals using or not using a gluten-free diet (3.00 vs. 2.90, p = 0.64). The prevalence ofgluten-free diet did not vary by education status (com-pleted high school vs. not, data not shown). Severalbiochemical, anthropomorphic and behavioral charac-teristics according to gluten-free diet adherence arepresented in Table I.

Discussion

To the authors’ knowledge, there are no data usingself-report gluten-free diet status as a surrogate for theprevalence of non-celiac gluten sensitivity in the gen-eral US population. Currently, the authors have esti-mated the prevalence of adherence to a gluten-free diet among the US residents to be 0.548%(95% CI 0.206–0.889). The prevalence tends to behigher among females, older individuals and non-Hispanic Blacks. These findings were not statisticallysignificant although there was limited statistical powergiven the low number of individuals reporting agluten-free diet.To the degree that self-report gluten-free diet data

can be used to approximate non-celiac gluten sensi-tivity prevalence, the current results suggest the prev-alence to be almost half the prevalence of celiacdisease [3–5]. This finding is noteworthy, as currentclinical inference has suggested that non-celiac glutensensitivity is far more common than celiac disease[24,25]. These impressions are likely influenced bythe high proportion of celiac disease cases that areundiagnosed in the general population [16].Adhering to a gluten-free diet could lead to iron

and vitamin B deficiencies [26–30]. The authorshave found that individuals using a gluten-free diettended to have lower serum iron and hemoglobinlevels as compared with those not on a gluten-free diet. By contrast, folate levels were not differentbetween participants adhering or not adhering to agluten-free diet.Participants on a gluten-free diet were more likely

to be normal weight and have lower CRP levels.Despite elevated LDL-cholesterol, gluten-free dietwas also associated with elevated higher HDL-cholesterol and a lower total cholesterol to HDL-cholesterol ratio. These results are consistent withprevious reports regarding the effects of a gluten-free diet [31] and extends previous findings to aceliac disease-free population on a gluten-free dietsupporting the notion that a gluten-free diet mighthave beneficial effects on HDL and BMI [31,32].

0< 19 19–39

Age (years)39–65 ≥ 65

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0.6

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Figure 1. Prevalence of adherence to a gluten-free diet stratified byage (years). Results from the Continuous National Health andNutrition Examination Survey 2009–2010.

0< 19 19–39

Age (years)39–65 ≥ 65

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p = 0.35p = 0.153

11.21.4

Figure 2. Prevalence of adherence to a gluten-free diet stratified byage (years) and gender. Results from the Continuous NationalHealth and Nutrition Examination Survey 2009–2010.Grey = Male, White = Female.

Prevalence of gluten-free diet adherence 923

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Using self-report gluten-free diet as a surrogate fornon-celiac gluten sensitivity has several possible lim-itations. Lack of gold standard intestinal biopsy datamight have caused the authors to exclude from theiranalysis, participants with self-report celiac diseasewho were actually non-celiac gluten sensitive; thiswould have led to non-celiac gluten sensitivityunderestimation. Alternatively, without data on IgAdeficiency, true celiac cases might have gone undiag-nosed, been included in the current sample andinappropriately considered to be non-celiac glutensensitive, resulting in overestimation. Additionally,it is possible that some individuals chose to partakein the gluten-free diet due to its perceived healthyattributes or for reasons unrelated to gluten-avoid-ance (i.e. wheat allergies) although these explanationslikely have minimal impact on the findings as wheatallergy is mainly a pediatric disorder that disappears inadulthood [7] and adherence to a gluten-free diet ischallenging [33]. The magnitude and net influence ofmisclassification in these data cannot be estimated.

Future studies that can more carefully evaluate indi-viduals reporting a gluten-free diet are necessary sothat intestinal biopsy and IgA deficiency data can beincorporated to minimize these possible sources ofbias.Using gluten-free diet as a surrogate for non-

celiac gluten sensitivity, the authors estimate theprevalence of non-celiac gluten sensitivity to be0.548% during the time period 2009–2010 amonga nationally representative sample of the US residents.These data suggest that the prevalence of non-celiac gluten sensitivity in the USA may have beenpreviously overstated [25,34]. Future studies will benecessary to more precisely estimate the prevalence ofnon-celiac gluten sensitivity and understand whethera gluten-free diet has a causal affect on general healthstatus.

Declaration of interest: The authors report noconflict of interest. The authors alone are responsiblefor the content and writing of the paper.

Table I. Characteristics of selected health indicators among those with and without non-celiac gluten sensitivity.

Gluten-free diet (n = 49)0.548% (0.206–0.889)

(1,380,381)*

No gluten-free diet (n = 7762)99.45% (99.11–99.79)

(250,653,383)* p-value

Waist circumference (cm) 88.2 (83.2–93.3) 93.9 (93.1–94.7) 0.03Systolic blood pressure (mm Hg) 123.9 (117.3–130.4) 117.8 (116.7–118.8) 0.07White blood cell count (1000 cells/ml) 6.78 (6.23–7.34) 7.08 (7.01–7.16) 0.03Hemoglobin (g/dl) 14.0 (13.6–14.4) 14.1 (14.0–14.2) 0.59Hematocrit (%) 41.3 (40.3–42.3) 41.1 (40.8–41.4) 0.69Red cell distribution width (%) 13.1 (12.7–13.5) 12.7 (12.67–12.8) 0.11HbA1c (%) 5.84 (5.43–5.93) 5.57 (5.54–5.61) 0.10Mean platelet volume (fl) 7.88 (7.55–8.19) 7.79 (7.66–7.93) 0.64TSH (mlU/ml) 1.48 (1.00–1.95) 2.02 (1.75–2.30) 0.05Total cholesterol (mg/dl) 216.1 (180.9–251.3) 189.1 (187.0–191.1) 0.11Direct HDL-cholesterol (mg/dl) 63.5 (53.5–74.5) 52.9 (52.2–53.8) 0.05Total cholesterol to HDL-cholesterol ratio 3.71 (3.37–4.05) 3.87 (3.82–3.91) 0.34LDL-cholesterol (mg/dl) 132.8 (84.3–181.3) 112.3 (110.2–114.5) 0.37CRP (mg/l) 2.94 (1.69–4.19) 3.32 (3.07–3.56) 0.55Serum folate (ng/ml) 20.2 (14.2–26.2) 19.5 (18.9–20.2) 0.82Iron (mg/dl) 77.2 (63.8–90.6) 87.5 (86.2–88.7) 0.14Total calcium (mg/dl) 9.55 (9.40–9.70) 9.47 (9.45–9.49) 0.26hs-CRP level (%)Low (<1.0 mg/l) 50.0 (35.8–64.3) 42 (39.1–44.2)Intermediate (1.0–3.0 mg/l) 31 (15.5–45.9) 30 (28.5–31.8)High (‡3.0 mg/l) 19 (10.6–28.0) 28 (26.5–29.9) 0.32

BMIUnderweight (%) 4 (0–7) 3 (2–3)Normal 54 (36–71) 35 (28–32)Overweight 16 (0–32) 30 (28–32)Obese 26 (16–37) 32 (31–35) 0.12

Iron deficiency anemia (%) 9.8 (1.39–18.3) 6.5 (5.69–7.38) 0.34Current smoker (%) 24 (5.03–42.2) 46 (42.4–48.5) 0.13

Results from the Continuous National Health and Nutrition Examination Survey 2009–2010.*Represents 95% CI for estimates; () represents estimated # of individuals in the USA.Abbreviations: BMI = body mass index; CI = confidence interval; CRP = C-reactive protein; HbA1c = hemoglobin; HDL = high-density lipoprotein; LDL = low-density lipoprotein; TSH = thyroid-stimulating hormone.

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