Intake and sources of gluten in 20- to 75-year-old Danish adults: a national dietary survey

Abstract

Purpose:
Celiac disease, an immunological response triggered by gluten, affects ~1 % of the Western population. Information concerning gluten intake in the general population is scarce. We determined intake of gluten from wheat, barley, rye and oat in the Danish National Survey of Diet and Physical Activity 2005-2008. The study population comprised a random cross-sectional sample of 1494 adults 20-75 years, selected from the Danish Civil Registration System.

Methods:
Protein content in wheat, rye, barley and oat was determined from the National Danish Food Composition Table and multiplied with the amount of cereal used in recipes. Amount of gluten was calculated as amount of cereal protein ×0.80 for wheat and oat, ×0.65 for rye and ×0.50 for barley. Dietary intake was recorded daily during seven consecutive days in pre-coded food diaries with open-answer possibilities.

Results:
Mean total gluten intake was 10.4 ± 4.4 g/day (10th-90th percentiles; 5.4-16.2 g/day), in men 12.0 ± 4.6 g/day and 9.0 ± 3.4 g/day in women. It was higher among men than among women in all age groups (20-75 years; P < 0.0001); however, this difference was eliminated when adjusting for energy intake. Intake of different gluten sources tended to be higher in men than in women with the exception of gluten from barley. Total gluten intake decreased with increasing age (P < 0.0001) as did gluten intake from wheat (P < 0.0001), whereas intake of gluten from rye (P < 0.0001) and barley (P = 0.001) increased with increasing age, also when adjusted for energy intake or body weight.

Conclusion:
This study presents representative population-based data on gluten intake in Danish adults. Total gluten intake decreased with increasing age.

Full text

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Eur J Nutr
DOI 10.1007/s00394-015-1062-3
ORIGINAL CONTRIBUTION
Intake and sources of gluten in 20‑ to 75‑year‑old Danish adults: a
national dietary survey
Camilla Hoppe1 · Rikke Gøbel2 · Mette Kristensen3 · Mads Vendelbo Lind4,5 ·
Jeppe Matthiessen1 · Tue Christensen1 · Ellen Trolle1 · Sisse Fagt1 ·
Mia Linda Madsen2 · Steffen Husby5
Received: 18 December 2014 / Accepted: 25 September 2015
© Springer-Verlag Berlin Heidelberg 2015
×0.50 for barley. Dietary intake was recorded daily dur-
ing seven consecutive days in pre-coded food diaries with
open-answer possibilities.
Results Mean total gluten intake was 10.4 ± 4.4 g/
day (10th–90th percentiles; 5.4–16.2 g/day), in men
12.0 ± 4.6 g/day and 9.0 ± 3.4 g/day in women. It was
higher among men than among women in all age groups
(20–75 years; P < 0.0001); however, this difference was
eliminated when adjusting for energy intake. Intake of dif-
ferent gluten sources tended to be higher in men than in
women with the exception of gluten from barley. Total glu-
ten intake decreased with increasing age (P < 0.0001) as
did gluten intake from wheat (P < 0.0001), whereas intake
of gluten from rye (P < 0.0001) and barley (P = 0.001)
increased with increasing age, also when adjusted for
energy intake or body weight.
Conclusion This study presents representative popula-
tion-based data on gluten intake in Danish adults. Total glu-
ten intake decreased with increasing age.
Keywords Gluten · Wheat · Oats · Barley · Rye · Danish ·
Adults
Introduction
Celiac disease (CD) is characterized as a state of height-
ened immunological responsiveness to ingested gluten
(from wheat, barley or rye) in genetically susceptible indi-
viduals [1]. At the same time, CD is a multi-organ disease
with a wide variety of gastrointestinal and extra-intestinal
manifestations varying in nature and severity, which may
become symptomatic at all ages [2]. Untreated CD is asso-
ciated with a number of complications, e.g., chronic diar-
rhea, abdominal pain, anemia and growth problems in
Abstract
Purpose Celiac disease, an immunological response trig-
gered by gluten, affects ~1 % of the Western population.
Information concerning gluten intake in the general popula-
tion is scarce. We determined intake of gluten from wheat,
barley, rye and oat in the Danish National Survey of Diet
and Physical Activity 2005–2008. The study population
comprised a random cross-sectional sample of 1494 adults
20–75 years, selected from the Danish Civil Registration
System.
Methods Protein content in wheat, rye, barley and oat
was determined from the National Danish Food Composi-
tion Table and multiplied with the amount of cereal used
in recipes. Amount of gluten was calculated as amount of
cereal protein ×0.80 for wheat and oat, ×0.65 for rye and
* Tue Christensen
tuchr@food.dtu.dk
1 Division of Nutrition, National Food Institute, Technical
University of Denmark, Mørkhøj Bygade 19, 2860 Søborg,
Denmark
2 Faculty of Health and Medical Sciences, Center for Basic
Metabolic Research, University of Copenhagen,
Copenhagen, Denmark
3 Department of Nutrition, Exercise and Sports, Faculty
of Science, University of Copenhagen, Copenhagen,
Denmark
4 Food and Nutrition Science, Department of Biology
and Biological Engineering, Chalmers University
of Technology, Gothenburg, Sweden
5 Hans Christian Andersen Children’s Hospital, Odense
University Hospital/University of Southern Denmark,
Odense, Denmark

Eur J Nutr
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infancy and childhood as well as osteoporosis and cancer
later in life [3, 4]. Historically, CD has been considered to
be uncommon, but recent studies in a number of popula-
tions have shown that CD affects around 1 % of the general
population [5–9]. The prevalence appears to be increasing
[10–14], which may partly be caused by increased aware-
ness and improved diagnostic procedures. Additionally,
there seems to be a relationship between type 1 diabetes
and gluten intake [15], and type 1 diabetes and CD may be
overlapping [16]. In addition to CD, a condition referred to
as non-celiac gluten sensitivity (NCGS) has been described
[17]. These patients also benefit from a strictly gluten-free
diet, although allergic and autoimmune reactions have been
ruled out.
Gluten is found in wheat, rye and barley and refers to
a range of complex protein structures, and mainly two
types exist: the ethanol-soluble prolamins and the etha-
nol-insoluble glutenins [18]. The prolamines in wheat are
named gliadins, and the related proteins in rye and barley
are named secalins and hordeins, respectively. These have
been reported to exert similar detrimental responses in
CD patients [19]. Oats also contain gluten prolamins and
avenins, and it is still debated to which extent this should
be grouped with the other prolamins, as oats appear to be
harmless to most CD patients [20, 21]. However, a small
subset of celiac patients may be intolerant to the avenin
proteins, which make up only about 10 % of the total
proteins of oats [22]. Therefore, we included oat-derived
gluten in the analyses to make it possible to differentiate
between the gluten intake from wheat, barley, rye and oats.
Information concerning gluten intake in the general
population is scarce [23], and more information is needed
on population intake for setting up clinical trials, for exam-
ple, to determine how much gluten should be consumed
to reflect conditions for the general population. It is also
important to look at different population subgroups as
these might be targeted individually in future trials. Fur-
ther, information on population intake makes it possible
to determine whether gluten intake in various diseases and
conditions is any different from that of the general popu-
lation. We therefore determined the intake of gluten from
wheat, barley, rye and oats cross-sectionally in the Danish
National Survey of Diet and Physical Activity (DANSDA).
These data can be used to compare gluten intake in future
trials to that of an average population but also in targeted
population groups.
Subjects and methods
The study was conducted according to the guidelines laid
down in the Declaration of Helsinki II and was approved by
the Danish Data Protection Agency (j.no. 2008-54-0430).
According to the Danish National Committee on Health
Research Ethics, studies with no intervention and with no
invasive procedures, like the present study, in which only
dietary intake was recorded, do not require approval from
the committee. Verbal informed consent was obtained from
all subjects prior to the study.
Population
This study was based on data from the DANSDA 2005–
2008, which is a nation-wide and representative cross-sec-
tional survey among 4- to 75-year-old children and adults.
The study population comprised a simple random sam-
ple of 20- to 75-year-old adults selected from the Central
Office of Civil Registration [24]. Individuals who did not
speak Danish, boarding school students, disabled individu-
als and nursing home residents were excluded. Participants
received an invitation letter containing the participant infor-
mation and were then contacted by a trained, experienced
interviewer by telephone, and an appointment was made at
the participant’s home for a personal interview about back-
ground information, and instruction in filling in the food
record was made.
Overall participation rate was 53.3, 50.3 % for men and
56.3 % for women [25]. Examination of under-/over-report-
ers [26, 27] showed that 73 % of the participants were clas-
sified as acceptable reporters, 26 % as under-reporters and
1 % as over-reporters.
Anthropometric variables
Self-reported information about height and weight was
obtained through the personal face-to-face interview with
the participants. Body mass index (BMI) was calculated
from weight and height of the participants by dividing
body weight in kilograms by height in meters squared
(kg/m2).
Dietary intake
Dietary intake was recorded every day for seven consecu-
tive days in food records with pre-coded response catego-
ries, which included open-answer options. The amount
of foods eaten was given in predefined household meas-
ures (cups, spoons, slices, etc.) or estimated from photos
of various portion sizes. For food items not included in
the pre-coded food record, the participants wrote the type
of food and portion size eaten in open-answer categories.
Participants also received a food record booklet to take to
the workplace or to other places outside of the home on the
days of food recording. Details about the method and cal-
culation of intake of food and nutrients have been described
elsewhere [28].

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Table 1 Characteristics of the
study population (n = 1494)
(mean values and standard
deviations; percentages)
20–34 years
(n = 344)
35–44 years
(n = 341)
45–54 years
(n = 284)
55–64 years
(n = 306)
65–75 years
(n = 219)
Mean SD Mean SD Mean SD Mean SD Mean SD
Age (years)
M 27.9 4.37 39.3 3.0 49.8 2.9 59.6 2.8 69.2 2.9
F 27.8 4.18 39.8 2.8 49.8 2.9 59.5 2.7 69.4 3.1
P*0.967 0.135 0.854 0.647 0.657
Educationa
Basic school (%)
M 19 17 15 16 20
F 12 6 6 19 43
Vocational education (%)
M 44 44 46 48 49
F 37 37 41 43 33
Short higher education (%)
M 13 13 6 5 8
F 9 9 11 8 6
Long higher education (%)
M 24 26 33 31 23
F 42 48 32 30 18
P** 0.035 <0.0001 0.432 0.471 0.004
Urbanization
Capital city area (%)
M 19 18 13 14 12
F 27 19 11 14 13
Towns ≥100.000 inhab. (%)
M 15 9 8 5 6
F 14 9 12 8 10
Towns 10.000–99.999 inhab. (%)
M 27 25 23 28 28
F 24 25 28 26 27
Towns 500–9.999 inhab. (%)
M 17 29 29 29 36
F 22 26 28 29 34
Towns <500 inhab. (%)
M 22 19 27 24 18
F 13 21 21 23 16
P** 0.096 0.983 0.423 0.954 0.822
BMI (kg/m2)
M 24.9 3.6 25.9 3.7 25.9 4.2 26.8 3.8 26.3 3.5
F 24.0 4.5 24.4 4.7 24.9 4.8 25.0 4.0 25.4 4.3
P*0.049 0.002 0.068 <0.0001 0.092
Weight status
Overweight (%)
M 31 39 41 47 50
F 22 20 26 32 34

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Cereals were recorded in numerous foods in the pre-
coded dietary record. Participants were able to record two
types of rye bread, wheat bread (plain), wholemeal wheat
bread, hard bread, crackers, croissant, Danish pastry, cakes,
pancakes, pita bread, different types of bread containing
fast foods as burgers, pizzas, sausage rolls and hot dogs,
as well as four types of breakfast cereals, oatmeal and
other hot cereals in addition to open-answer possibilities.
The recipes in the dietary survey are based on commonly
used recipes in major Danish cookbooks as well as updated
information on market shares of purchased food products
in the Danish retail sector.
Gluten content in food items
All food products containing wheat, oat, barley and rye
were considered as containing gluten. From all food prod-
ucts reported in the food record, the gluten content of these
cereals was calculated as previously described [29]. Briefly,
since there is no information in food composition tables on
the gluten content of food products, the estimated amount
of protein from gluten-containing cereals according to the
Danish Food Composition Databank [30] was multiplied by
0.8 for wheat and oat [23, 31], by 0.65 for rye [32] and by
0.50 for barley [33]. The amount of gluten-containing cere-
als in composite foods was estimated from recipe informa-
tion from producers or the recipes used in the dietary survey.
Intakes of energy, nutrients and food items were calcu-
lated for each individual using the software system GIES
(version 1.000d; developed at National Food Institute,
Technical University of Denmark) and the Danish Food
Composition Databank [30].
Statistical analyses
All data were analyzed with the Statistical Package for the
Social Sciences software (version 21; IBM SPSS Statistics,
Inc., Chicago, USA), and a significance level of P < 0.05
was used (2-tailed tests). Results are shown as mean ± SD.
Analysis of variance (ANOVA) was applied to test for dif-
ferences in gluten intakes [absolute intake (mg/day), intake
per energy intake (mg/kJ) and intake per body weight (mg/
kg)] between gender (male; female), except for weight sta-
tus, educational level and urbanization which was deter-
mined with a χ2 test, and for differences in gluten intakes
[absolute intake (mg/day), intake per energy intake (mg/kJ)
and intake per body weight (mg/kg)] between age groups
(20–34, 35–44, 45–54, 55–64, 65–75 years). Post hoc com-
parisons across age groups were made using Bonferroni’s
post hoc test.
Results
Participant characteristics
As previously described [25], the distribution of gender and
age of the participants could be characterized as representa-
tive for the Danish population, aged 20–75 years in com-
parison with census data from Statistics Denmark. Data
from a total of 1494 adults were available and included in
the present study.
Characteristics of the study population are given in
Table 1. Women had higher educational levels than men,
reaching statistical significance in the 20- to 34-year-olds
(P = 0.035), in the 35- to 44-year-olds (P < 0.0001) and
in the 65- to 75-year-olds (P = 0.004). There were no
gender differences regarding urbanization in any of the
age groups. Men had higher BMI than women in all age
groups, but this only reached statistical significance in the
20- to 34-year-olds (P = 0.049), in the 35- to 44-year-olds
(P = 0.002) and in the 55- to 64-year-olds (P < 0.0001).
Also, there were more overweight men than women in 35-
to 64-year-olds (P ≤ 0.021).
20–34 years
(n = 344)
35–44 years
(n = 341)
45–54 years
(n = 284)
55–64 years
(n = 306)
65–75 years
(n = 219)
Mean SD Mean SD Mean SD Mean SD Mean SD
Obese (%)
M 8 13 13 19 10
F 9 14 12 11 16
P** 0.192 <0.0001 0.021 <0.0001 0.051
Table 1 continued
M males, F females, BMI body mass index
* ANOVA test for difference between men and women within the same age group
** χ2 test for difference between men and women within the same age group
a Basic school; 10 years or less of total education, vocational education; upper secondary school,
10–12 years, short higher education; 13–15 years, primarily theoretical, long higher education; 15+ years,
primarily theoretical

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Table 2 Percentiles of gluten
intake in (a) Danish men
(n = 677), 20–75 years, (b)
Danish women (n = 817),
20–75 years
Age (years) nPercentiles
10 20 30 40 50 60 70 80 90
(a)
Total gluten intake (mg/day)
20–34 132 7148 9035 11,039 12,305 13,556 14,281 15,247 17,720 20,111
35–44 146 7444 9316 10,043 11,053 11,206 13,435 15,105 16,498 19,179
45–54 132 5797 7328 8894 10,237 11,236 12,866 14,783 16,491 18,264
55–64 148 5349 7285 8709 9759 10,658 11,953 12,932 14,076 15,181
65–75 119 5566 6708 8038 8958 10,245 11,382 12,309 14,138 16,414
Total gluten intake, except from oats (mg/day)
20–34 132 6525 7906 9451 10,631 11,417 12,223 13,357 14,113 16,678
35–44 146 6307 7888 8675 9512 10,530 11,824 12,821 14,680 16,133
45–54 132 5119 6631 7810 8884 9864 10,711 12,175 13,867 15,794
55–64 148 4473 6277 7149 8177 8796 9543 10,455 11,817 13,133
65–75 119 5070 6154 6883 7563 8205 9106 10,194 10,975 13,001
Gluten intake from wheat (mg/day)
20–34 132 4882 6160 6991 7864 8927 9990 10,643 12,467 14,817
35–44 146 4212 5226 6211 7276 8102 8946 9957 11,117 13,182
45–54 132 2835 4022 5307 5816 6598 7546 8382 9432 11,628
55–64 148 2222 3218 3925 4790 5687 6441 7353 8153 9393
65–75 119 2300 3335 3977 4519 5231 5812 6685 7705 8643
Gluten intake from oats (mg/day)
20–34 132 310 489 579 773 1009 1206 1633 3368 5950
35–44 146 377 493 627 755 931 1232 1686 2653 5048
45–54 132 278 427 563 745 913 1180 1834 2862 4479
55–64 148 203 367 605 728 968 1352 2130 3299 4950
65–75 119 155 314 502 690 974 1199 2087 3625 5649
Gluten intake from barley (mg/day)
20–34 132 0.63 1.24 2.35 4.19 5.96 10.3 12.3 17 25.7
35–44 146 0.7 1.56 2.93 5.24 6.39 9.02 11.9 18.4 36.3
45–54 132 0.68 1.2 2.94 5.14 6.68 11.8 17.8 24 31.1
55–64 148 0.68 1.15 1.53 2.92 4.94 8.12 10.8 19.5 30.6
65–75 119 0.7 0.99 1.2 1.64 3.57 6.2 9.94 15.5 21.6
Gluten intake from rye (mg/day)
20–34 132 483 894 1283 1647 42,004 2522 2916 3453 3965
35–44 146 745 1101 1417 1844 2224 2843 3254 4051 5251
45–54 132 1009 1500 1877 2223 2917 3239 3887 4666 6218
55–64 148 1048 1499 2008 2620 3033 3482 3842 4398 5534
65–75 119 1375 1972 2289 2583 2853 3273 3757 4284 5456
(b)
Total gluten intake (mg/day)
20–34 212 5253 6640 7715 8958 9632 10,507 11,573 12,391 14,367
35–44 195 5921 7213 8135 8864 9565 10,397 11,354 12,449 14,560
45–54 152 4418 5779 6534 7817 8366 9051 9887 10,990 13,029
55–64 158 4164 5456 6057 6800 7338 8014 8912 9736 11,474
65–75 100 4895 5672 6508 7102 7672 8269 8995 10,664 11,675
Total gluten intake, except from oats (mg/day)
20–34 212 4598 5710 6678 7416 8191 8941 9744 10,787 12,609
35–44 195 4905 6069 6860 7589 8132 8711 9837 10,827 12,430
45–54 152 3900 4776 5563 6374 7216 7919 8817 9533 10,774

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Diet and gluten intake
Mean total gluten intake in the entire study population was
10,371 ± 4405 and 8777 ± 3631 mg/day with and without
gluten derived from oats, respectively. The 10th and 90th
percentiles were 5373 and 16156 mg/day, respectively,
including gluten from oats, and 4530 and 13591 mg/day,
respectively, excluding gluten from oats. Gluten derived
from wheat constituted 62 % of the gluten intake, including
gluten from oats, and 72 % excluding gluten from oats.
In Table 2, percentiles of gluten intakes in men and
women are listed separately. Mean total gluten intake was
12037 ± 4593 mg/day in men and 8991 ± 3385 mg/day in
women. Men had higher intakes of gluten than women in
all age groups (P < 0.0001) (Fig. 1), which corresponds to
their higher energy intake (data not shown). The intake of
different gluten types also tended to be higher in men than
in women with the exception of gluten from barley (Fig. 1).
Total gluten intake decreased with increasing age
(P < 0.0001), as did gluten intake from wheat (P < 0.0001).
Gluten intake from oats remained unchanging throughout
the age groups (P = 0.476), and the intake of gluten from
rye (P < 0.0001) and barley (P = 0.001) increased with
increasing age, independent of energy intake (Table 3) and
body weight (data not shown).
Bread contributed most to total gluten intake in all age
groups (Table 4), followed by breakfast cereals and pasta.
Regarding wheat, bread and pasta contributed the most,
whereas regarding oats, breakfast cereals contributed the
most.
Discussion
In the present study, we found that mean total gluten intake
was 10.4 ± 4.4 g/day, where 62 % derived from wheat and
8.8 ± 3.6 g/day not including oat. Also, we found that men
consumed more gluten than women, however not when
adjusting for energy intake, and that gluten consumption
decreased with age independent of energy intake and body
weight, suggesting that the diet of elderly individuals con-
tains less gluten than that of the younger population.
Table 2 continued Age (years) nPercentiles
10 20 30 40 50 60 70 80 90
55–64 158 3629 4611 5422 5976 6590 7273 7758 8727 10,174
65–75 100 3744 4587 5317 6109 6700 7073 7826 8467 10,086
Gluten intake from wheat (mg/day)
20–34 212 3497 4353 5268 5812 6602 7266 7770 9080 10,343
35–44 195 3490 4352 5038 5593 6164 6960 7588 8456 9781
45–54 152 2458 3228 3845 4532 4979 5632 6161 7181 7903
55–64 158 2061 2854 3531 4094 4383 4857 5518 5966 7444
65–75 100 1985 2615 3134 3731 4206 4737 5364 6402 7233
Gluten intake from oats (mg/day)
20–34 212 275 425 549 737 919 1187 1750 2245 3454
35–44 195 282 421 570 756 922 1238 1677 2352 3209
45–54 152 207 342 456 593 792 960 1455 2034 2980
55–64 158 132 251 321 427 547 650 861 1251 2332
65–75 100 222 335 432 556 665 893 1280 2000 3143
Gluten intake from barley (mg/day)
20–34 212 0.85 2.36 3.73 5.67 7.66 11.3 15.4 20.5 29.6
35–44 195 1.01 3.33 6.05 8.57 11.4 13.8 17.6 23.3 34
45–54 152 0.57 1.19 3.57 6.48 9.12 11.8 15.8 19.6 29.8
55–64 158 0.54 0.99 3.19 4.09 6.93 9.84 13.3 20.2 32.2
65–75 100 0.61 0.89 1.33 2.55 4.29 8.34 12.5 17.9 23.5
Gluten intake from rye (mg/day)
20–34 212 394 727 984 1159 1433 1631 1940 2346 3124
35–44 195 695 973 1299 1541 1786 2009 2429 2804 3789
45–54 152 809 1065 1352 1698 1918 2215 2466 2811 3584
55–64 158 662 1004 1389 1668 1962 2246 2741 3097 3523
65–75 100 1096 1439 1663 1863 2181 2395 2838 3169 3506

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These data are less than the previously reported mean
gluten intake of 13.1 g/day among Dutch adults [23]. Gen-
erally, the Danish dietary patterns are similar to those seen
among the Dutch, but this difference in gluten intake may
be caused by a combination of differences in intake of vari-
ous types of cereals and the different methods applied to
estimate gluten intake from different sources, as the esti-
mated amount of protein from gluten-containing cereals
was multiplied by 0.8 for wheat and oat [23, 31], by 0.65
for rye [32] and by 0.50 for barley [33] in the present study
and by 0.8 for all grain types in the Dutch study [23]. Here,
information on the different sources of gluten was not
Fig. 1 Daily intake of gluten
(mg/day, 95 % CI) from oats,
wheat, rye and barley, and total
gluten in 1494 20- to 75-year-
old Danish men and women. a
20- to 34-year-olds (n = 344).
Differences between men
(dark bars) and women (light
bars) (oats, P = 0.012; wheat,
P < 0.0001; rye, P ≤ 0.0001;
barley, P = 0.074; total,
P < 0.0001). b 35- to 44-year-
olds (n = 341). Differences
between men (dark bars) and
women (light bars) (oats,
P = 0.089; wheat, P < 0.0001;
rye, P < 0.0001; barley,
P = 0.116; total, P < 0.0001). c
45- to 54-year-olds (n = 284).
Differences between men
(dark bars) and women (light
bars) (oats, P = 0.008; wheat,
P < 0.0001; rye, P < 0.0001;
barley, P = 0.979; total,
P < 0.0001). d 55- to 64-year-
olds (n = 306). Differences
between men (dark bars) and
women (light bars) (oats,
P < 0.0001; wheat, P < 0.0001;
rye, P < 0.0001; barley,
P = 0.878; total, P < 0.0001). e
65- to 75-year-olds (n = 219).
Differences between men
(dark bars) and women (light
bars) (oats, P = 0.008; wheat,
P = 0.004; rye, P < 0.0001;
barley, P = 0.744; total,
P < 0.0001). f 20- to 75-year-
olds (n = 1494). Differences
between men (dark bars) and
women (light bars) (oats,
P < 0.001; wheat, P < 0.001;
rye, P < 0.0001; barley,
P = 0.037; total, P < 0.0001)

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provided, but likely rye and barley contributed little to the
total gluten intake as these are not commonly consumed
cereals in the Netherlands.
Remarkably, intake of gluten from wheat decreased with
increasing age, whereas gluten intake from rye increased
with increasing age. This observation corresponds with
the fact that the intake of products with wheat, such as fast
food, was higher in the younger part of the population,
whereas the elderly individuals still seem to prefer cereal
products with rye, as suggested by the fact that rye glu-
ten from bread was increasing with increasing age, which
probably is due to the frequent use of rye bread in the Dan-
ish diet, in particular as part of a traditional lunch meal
[25]. Gluten from oats was derived mainly from breakfast
cereals, and rolled oats are a major ingredient in a typical
Danish breakfast meal [25]. In general, the consumption of
barley in Danish adults was very low and with quite a large
variation.
There were some strengths and limitations in the present
study. We have not been able to find any food databases
with detailed information on gluten content from wheat,
barley, rye and oats, and our calculations are approxi-
mate. As all studies relying on self-reporting, this study
may be affected by self-report bias. Both under-reporting
of energy as well as over-estimation of socially acceptable
foods might occur. However, the most common foods to
over-report are meat, fish, vegetables, salad and fruit, while
foods such as cakes, cookies, sugar, candies and fats might
be under-reported [34]. In that matter, bread is considered
a “neutral” food. Validation of the current dietary survey
indicated an underestimation of energy intake of approxi-
mately 12 % at group level [28].
The strengths of the study include the access to detailed
dietary data for 7 days that enabled analysis of the gluten
intake from different sources. Dietary data were collected
all year round to compensate for seasonal variation in food
intake. Furthermore, the pre-coded food diary covers both
week days and weekend days. The 7-day estimated food
record/diary is a prospective method, which is not affected
by the memory since the foods and beverages are recorded
close to the time of consumption. Another advantage of
the methods is that portion sizes can be more accurately
estimated compared to retrospective methods. The dietary
survey estimates the consumed amounts on the basis of
household measures, standard portions and photo series,
which can reduce the respondent burden compared to,
e.g., weighed dietary record. A less respondent burden can
ensure a more accurate estimation of the consumed foods.
In a comparison of dietary assessment methods, the 7-day
food record/dairy was found to give the best estimates of
dietary intake compared with FFQ and 24-h recall [35].
Validation of the current estimated food dairy against
weighed records has shown the ability to cross-classify in
good accordance with results of other validation studies,
thus making the pre-coded food diary an appropriate tool
for the classification of individuals according to high or low
intakes of nutrients [36].
Furthermore, the study was based on a random sample
of the Danish adult population including individuals with
a wide age range from both urban and rural areas, thus
likely to resemble the general population. In an earlier
study of the demographic composition of the DANSDA
participants, it was concluded that the study sample was
representative for the Danish adult population with respect
Table 3 Daily gluten intake in 20- to 75-year-old Danish adults (n = 1494) (mean values and standard deviation)
a, b, c, d values within a row with different superscript letters were significantly different for each gluten intake (ANOVA test with Bonferroni
post hoc test), P < 0.05
20–34 years
(n = 344)
35–44 years
(n = 341)
45–54 years
(n = 284)
55–64 years
(n = 306)
65–75 years
(n = 219)
Mean SD Mean SD Mean SD Mean SD Mean SD
Gluten (mg/day) 11209a4390 11252a4471 10207b4604 9239b3981 9478b4090
Total, except oats 9558a3744 9575a3667 8636b3672 7841b3227 7798b3318
Wheat 7722a3422 7283a3062 6007b2879 5229c2558 5053c2851
Oats 1651a1843 1677a1983 1571a2026 1398a1835 1680a2145
Barley 12a,b 13 14a13 13a,b 14 11a,b 14 9b12
Rye 1825a,b 1222 2278b,c 1580 2616c,d 1793 2601c,d 1636 2736d1401
Gluten per energy intake (mg/kJ) 1.20a0.34 1.20a0.32 1.13b0.31 1.07b0.35 1.09b0.31
Total, except oats 1.02a0.28 1.02a0.27 0.96b0.25 0.91b0.28 0.90b0.26
Wheat 0.82a,b 0.28 0.78b0.26 0.67c0.24 0.61d0.25 0.58d0.24
Oats 0.18a0.2 0.18a0.19 0.17a0.18 0.16a0.2 0.19a0.24
Barley 0.01a,b 0.01 0.02a0.02 0.01a,b 0.02 0.01a,b 0.02 0.01b0.02
Rye 0.20a,b 0.12 0.24b0.13 0.29c0.16 0.30c0.16 0.32c0.15

Eur J Nutr
1 3
to gender, age, urbanization, and education; however, the
younger men were slightly underrepresented, which, how-
ever, was considered not to influence the generalizability of
the results [25]. The influence of non-response bias cannot,
however, be excluded. Because of the high demand of the
study on participants, it is possible that responders consti-
tute a selected group of more motivated participants for a
healthy lifestyle than non-responders [37].
Recently, two large clinical trials [38, 39] have shown
no effect of the introduction of gluten in the infant diet
early or late or introduction of a small amount of gluten
concurrently with breastfeeding on the subsequent develop-
ment of celiac disease. Also there is no evidence that the
amount of gluten in the diet influences the risk of celiac
disease [40]. The scarce information about the level of glu-
ten intake in the general population and in population sub-
groups makes it difficult to set an appropriate level of glu-
ten intake in intervention trials. Further, comparing gluten
intake between disease states and a comparable population
requires a reliable determination of a normal gluten intake.
The data provided in this paper provide a framework for
further studies on the putative associations between quanti-
tative and qualitative gluten consumption and the manifes-
tations of CD as well as of the less well-established entity
NCGS and of other diseases such as type 1 diabetes melli-
tus that might be linked to gluten intake [15, 41]. A method
Table 4 Contribution of wheat,
oats, barley and rye and total
gluten intake from major food
groups in 20- to 75-year-old
Danish adults (n = 1494)
a Bread, bun, hard bread, biscuit, pretzel
b Corn flakes, rolled oat, muesli, porridge, Danish crumble
c Burger, taco, tortilla, pita, croissant, pizza, hot dog, French toast
d Pasta, cooked cereals
e Meatballs, vegetable balls, fish balls, liver paste, pâté, shellfish in pastry, cheese dippers, licorice
20–34 years
(n = 344)
35–44 years
(n = 341)
45–54 years
(n = 284)
55–64 years
(n = 306)
65–75 years
(n = 219)
Total gluten (mg/day)
Breada6461 7499 7375 7054 7240
Breakfast cerealsb1643 1716 1926 1800 2054
Fast foodc2627 1770 1247 1042 781
Pastad1027 847 646 414 478
Othere534 588 524 497 483
Wheat (mg/day)
Breada4196 4726 4301 4039 4080
Breakfast cerealsb39 41 45 85 114
Fast foodc2534 1708 1204 1008 753
Pastad1027 847 646 414 478
Othere505 549 499 466 454
Oats (mg/day)
Breada470 507 455 421 421
Breakfast cerealsb1108 1105 1081 939 1227
Fast foodc46 28 15 9.3 5.3
Pastad00000
Othere27 37 21 29 27
Barley (mg/day)
Breada9.1 12 11 10 8.1
Breakfast cerealsb0.9 0.9 0.6 0.5 0.5
Fast foodc1.6 1.2 0.6 0.4 0.5
Pastad00000
Othere00000
Rye (mg/day)
Breada1787 2254 2596 2584 2716
Breakfast cerealsb4.9 4.6 4.6 8.4 13
Fast foodc31 18 11 6.3 3.9
Pastad00000
Othere1.8 1.4 3.9 2.6 3.0

Eur J Nutr
1 3
could be to associate gluten consumption on an individual
basis with the subsequent development of CD, feasible in
large population-based surveys.
Conclusion
This study provides nationally representative population-
based data on gluten intake from different sources in 20- to
75-year-old Danish adults, with a mean total gluten intake
of 10.4 g/day, 12.0 g/day in men and 9.0 g/day in women.
The majority of ingested gluten was derived from wheat.
Total gluten intake decreased with increasing age as did
gluten intake from wheat, whereas intake of gluten from
rye and barley increased with increasing age, also when
adjusted for energy intake and body weight.
Acknowledgments The authors wish to thank Data Warehouse
Manager Karsten Kørup and Data Scanning Manager Hanne-Jette
Hinsch as well as Majken Ege and Karin Hess Ygil (Division of
Nutrition, National Food Institute, Technical University of Denmark)
for contributing to the data processing. The authors express their
gratitude to all the participating children and parents in DANSDA.
The authors conceived the study (C.H., S.H.), designed the analyses
of this study (C.H.) and were responsible for the design and collec-
tion of data from the Danish National Survey of Diet and Physical
Activity (S.F., J.M., E.T.) and responsible for data interpretation and
processing (T.C.). C.H. was responsible for analyses of data and writ-
ing the manuscript. All authors participated in the discussion of the
results and revision of the manuscript. This study was supported by
the Danish Strategic Research Council (Project No. 09-06-5149), and
the Danish National Survey of Diet and Physical Activity (DANSDA)
was financed by the Ministry of Food, Agriculture and Fisheries.
Compliance with ethical standards
Conflict of interest None of the authors have declared any conflict
of interest.
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