Disorders triggered by wheat/gluten include celiac disease (CD), which is also triggered by gluten from rye and barley, wheat allergy (WA) and non-celiac gluten sensitivity (NCGS). CD is a T cell-mediated autoimmune-like enteropathy associated with inflammation. The hallmark of IgE-mediated WA is the presence of anti-wheat IgE antibodies in patients’ blood with the appearance of symptoms after wheat exposition [1
]. NCGS has a wide spectrum of clinical manifestations that commonly overlap with irritable bowel syndrome and CD [2
]. However, NCGS pathogenesis is still unclear and there is a lack of sensible and reproducible biomarkers to aid in its diagnosis [4
]. Although experts have proposed criteria for NCGS diagnosis [5
], some gaps need to be filled before using the criteria in clinical practice [6
]. In this frame, the survey-based estimation of NCGS prevalence at population level has gained attention among researchers in the field. Additionally, the survey-based tools developed for such a purpose have allowed us to assess the observance of a dietary regime that avoids wheat/gluten (gluten-free diet, GFD). Adhering to a GFD or avoiding wheat from the diet (in WA cases) are the only accepted treatments for gluten-related disorders (GRD) [8
]. However, most people following the GFD are doing it for reasons other than health related benefits and without medical/dietitian advice probably compromising their health [9
]. In the last years, our research group has been perfecting and applying a tool in different Hispano American countries to estimate the prevalence rates of adverse reactions to gluten and adherence to a GFD [9
]. Based on specific definitions, the prevalence rates of self-reported GRDs can be estimated. Recently, the tool was validated in Brazilian-Portuguese [15
], opening the opportunity for carrying out a survey study in a country inhabited by almost half of the South American population. Thus, our aim was to estimate the prevalence rates of adverse reactions to gluten, of the disorders triggered by wheat/gluten ingestion and of following a GFD in two populations from Brazil.
The prevalence rates of GRDs and adherence to a GFD in adult Brazilian population were estimated by self-report. Other survey studies with the same design and carried out in Latin America by using the same instrument have reported lower response rates (53%–92%) than the rate obtained in the present study (93.2%) [9
]. It should be noted that this rate is ten-fold higher than the one reported in a pilot study carried out in Brazilian population, but an online platform was used to collect data [15
]. Online surveys are practical and economical mainly because they do not require trained human resources moving from one place to another. Unfortunately, our results confirm that the instrument utilized in the present study requires a survey design involving face-to-face interviews for obtaining high response rates.
Although attention should be paid to the definitions given to a specific GRD in particular studies, the pooled prevalence of self-reported GRD among studies carried in Latin America (3.1%–7.8%) [9
], Europe (6.2%–13%) [16
] and Australia (14.9%) [21
] range from 3.1% to 14.9%. The consumption of wheat has been related to the prevalence of GRD such as CD and/or NCGS [9
], the higher wheat/gluten consumption per capita the higher prevalence of GRD expected, but this notion seems not to apply for the Brazilian populations studied. Brazilians consume more wheat per capita (59.9 kg) than Mexicans (55.2 kg), Colombians (29.48 kg) and Salvadorans (34.34 kg) [23
], but the pooled self-reported prevalence of GRD was 2.33% in the present study. Certainly, this is the lowest prevalence rate of GRD ever reported among survey-based studies carried out in Latin American countries and elsewhere [9
]. Despite these findings, the main gastrointestinal and extra-intestinal symptoms informed by those who met criteria for SR-GS were the same as those reported in different populations [9
] including a Brazilian population suspected of NCGS [27
]. Overall, these data highlight the need for further population-based epidemiological studies preferentially including serology tests, HLA-typing (Human Leucocyte Antigen-typing), intestinal biopsies and an in-depth questionnaire.
The prevalence rate of SR-PD CD was 0.30%. This prevalence rate is even lower than that reported in other studies carried out in a Brazilian population (0.36%), which were based on biopsy-proven CD [28
]. Considering a general CD prevalence among populations between 0.5 and 1.0%, the results show a potential CD underdiagnosis in the Brazilian population. This potential underdiagnosis seems to be a common problem in some Latin American populations; for instance, among more than 1200 people surveyed in Mexico only 1 person met criteria for SR-PD CD [13
]. Similar findings were reported in studies carried out in El Salvador (2 SR-PD CD cases in 1326 people surveyed) [10
] and Colombia (no SR-PD CD cases in 1207 people surveyed) [14
]. Contrarily, a study carried out in Argentina reported a prevalence rate of SR-PD CD of 0.58% (7 cases in 1209 people surveyed) [9
]. This increase in CD diagnosis was attributed to the implementation of a nationwide program for the detection and control of CD and the subsidies given to the patients to help manage the cost of the GFD [9
]. No program or subsidies have been implemented in Brazil. Therefore, the estimated prevalence rate of SR-PD CD in the Brazilian adult population surveyed in this study shows that awareness of CD by Brazilians health professionals is better than in some other Latin American countries.
NCGS diagnosis is challenging due to the non-standardized and time-consuming diagnostic criteria as well as the lack of sensitive and reproducible biomarkers. In the present study, the self-reported NCGS prevalence rate was estimated including people that met criteria for SR-GS, but did not meet criteria for WA or CD [9
]. Under these criteria, the prevalence of NCGS in the Brazilian population studied was 1.7%. Utilizing the same criteria, this rate is higher than those reported in survey studies carried out in Mexico (0.16%), Colombia (0.82%), Argentina (0.91%), El Salvador (0.98%), The Unites States of America (0.54%) and Italy (slightly higher than 1%) [9
]. It should be noted that the NCGS prevalence rate reported in the present study is the highest among the populations evaluated utilizing the same criteria, but, paradoxically, the pooled prevalence of GRD is the lowest. As mentioned above, further studies including celiac serology and HLA typing will help to identify the potential CD cases that in survey studies meet criteria for NCGS. Regarding WA, the prevalence rate was 0.79%. This rate is in line with WA prevalence data estimated in other surveys carried out in Latin American countries (Mexico, Colombia, Argentina, El Salvador; 0.72, 0.74, 0.33, 0.75%, respectively) and utilizing the same instrument [9
]. The prevalence of food allergy, including wheat allergy (0.6%), in Brazilian infants was estimated by parent-report [29
], but, to our knowledge, this is the first study that estimate the prevalence of WA in Brazilian adult population.
Four out of five SR-PD CD cases identified in the present study informed that they were following a GFD. In other studies around 60% of the Brazilian physician-diagnosed CD patients informed to be following a strict GFD [30
]. This difference in the percentages of adherence to a GFD can be attributed to the targeted populations of each study and the number of physician-diagnosed CD cases surveyed (5 vs. 46). Although there is poor availability of gluten-free products in Brazil and the cost of these products is high compared to their regular counterparts [32
], the general prevalence of adherence to a GFD (7.48%) in the population studied is the highest among the prevalence rates reported in other surveys carried out in Latin America. Particularly, this prevalence rate is two-fold higher than the rate reported in a survey carried out in Mexico (3.7%) [13
], the high cost and poor availability of gluten-free products have been documented in Mexico [33
]. This highlights that there is not enough data to establish a clear association between the cost and availability of gluten-free products and the prevalence rates of adherence to a GFD, at least in Latin America. Younger age at the time of diagnosis and longer duration of disease, among others, are factors associated with poor adherence to a GFD in CD cases [34
]. Similarly, our results show that in the absence of a formally diagnosed GRD those aged ≥39 years old more frequently follow a GFD. Certainly, the motivations for adhering to the diet without a diagnosis of a GRD commonly include weigh control or a perceived general health benefit [9
]. In the present study, the non-SR-GS individuals commonly reported those motivations for following a GFD or avoiding wheat/gluten from their diets although there is not enough evidence to support health benefits of the GFD in the absence of GRD [37
] and the benefits and risks of following a GFD for this group of people are uncertain [12
]. Overall, most people who were following a GFD were doing it for reasons other than the treatment of a diagnosed GRD and 50% of the GFD cases were following the diet without medical/dietitian advice.