Background
Reported food hypersensitivity (FHS) is common in the Western countries. However, there are large differences in prevalence between studies. In a meta-analysis investigating FHS in 51 studies, the prevalence of self-reported FHS varied from 3 to 35% due to differences in study methods, age of study populations and geographic settings [
1]. The high and increasing prevalence of reported FHS [
2,
3] may partly be attributed to an increasing awareness about FHS in the population, as well as public interest of different diets [
4]. The term FHS includes food reactions of both immunological and non-immunological origins, and food allergy is a subgroup of FHS [
5].
Elimination of foods due to FHS may negatively affect the Health Related Quality of Life (HRQL) [
6]. HRQL can be defined as self-perceived health [
7] since it is possible to have a chronic disease but still experience a good self-perceived HRQL. Since HRQL is individual and varies with age [
6], it is suggested that when applicable, the questionnaires should be completed by the individuals themselves [
8]. Usually, children are able to complete their HRQL questionnaire from the age of eight years, given that the questionnaires are age appropriate and that the child have reading skills [
9]. Generic HRQL questionnaires are used for comparisons between different diseases, or between subjects with or without a disease [
10]. Disease-specific questionnaires investigate HRQL related to a specific disease, e.g. food allergy [
11].
The interest in HRQL in children and adolescents with food allergy has increased during the last decades, and a number of disease-specific HRQL questionnaires are now available for children [
11,
12], adolescents [
13,
14], and parents to children [
15‐
18] with IgE mediated food allergy. However, there is a limited number of HRQL questionnaires available for the wider definition FHS [
19,
20]. To our knowledge, no studies have explored HRQL among children with different phenotypes of FHS.
In a population-based cohort of schoolchildren, the paediatric cohort II within the Obstructive Lung Disease in Northern Sweden studies (OLIN), 5% of the children reported complete elimination of cow’s milk, hen’s egg, fish or wheat due to FHS at age 11–12 years [
21]. The aim of the current study was to compare HRQL among children with and without complete elimination of cow’s milk, hen’s egg, fish or wheat due to FHS, and to study HRQL in relation to different FHS phenotypes. Since milk, egg, fish and wheat are staple foods in Western diet, we hypothesised that avoidance of these foods would have a negative impact on HRQL.
Discussion
According to European norms [
10,
26], the children aged 12–13 years in this population-based study reported a good generic HRQL and there was no difference in HRQL between children with and without FHS. Further, no statistically significant differences in disease specific HRQL were found between children with the different FHS phenotypes: current food allergy, outgrown food allergy and lactose intolerance. However, the proportion of children having poor quality of life, defined as ≥75th percentile in the disease specific questionnaire, was more common in the current food allergy phenotype compared to the other phenotypes of FHS.
The participants in our study reported a good generic HRQL. Our result is in line with another Swedish population-based study comparing children aged eight years with or without atopic diseases including FHS. Overall, these children reported a good generic HRQL but children with atopic diseases, in particular asthma, had lower HRQL compared with children without atopic diseases [
32]. Other factors than the disease itself may have an impact on the HRQL e.g. parental income [
33], or being accepted by friends or not [
34]. A possible explanation for the good HRQL among children with FHS in our study, and others as well, may be that FHS is common among children in Northern Europe [
35]. Thus living with FHS or food allergy might be accepted as a normality and the restricted diet might therefore have a lesser impact on children’s daily life [
36,
37].
The increased availability of milk and gluten free products in Sweden may affect the HRQL in a positive way e.g. it is easier to prepare meals for children with different types of FHS. On the other hand, it probably also increases the awareness of different types of diets. People may regard temporary or non-specific symptoms as symptoms of FHS leading to an un-necessary eliminated diet [
4]. Interestingly, the participants in our study showed similar results compared to a Swedish study of randomly selected children aged 11–16 years, with the lowest score in the domain Physical wellbeing [
38].
Country of origin may have an impact of HRQL. The Food Allergy Quality of Life Questionnaire-parent form was completed by parents of 1029 food allergic children from different parts of the US. The result was compared with 15 studies from different countries in Europe, using the same questionnaire. The HRQL was more impaired in the US population than the European populations [
39]. Thus, it is important that translation and validation of HRQL questionnaires includes lingual as well as cultural translations, due to socioeconomic and cultural differences between countries [
40].
To our knowledge, this is the first study investigating HRQL among different phenotypes of FHS in the general population. A number of hospital-based studies have described quality of life in children with IgE-mediated food allergy [
13,
33,
41]. In hospital materials, poor HRQL has been related to severe symptoms to foods e.g. anaphylaxis, respiratory or cardiovascular symptoms [
33,
41], multiple food allergies [
11,
33,
41], comorbidity with atopic diseases [
41] or allergy to specific foods e.g. cow’s milk and hen’s egg compared to allergy to peanuts or tree nuts [
33]. In our population-based study, we did not find any statistical significant differences in HRQL between children with and without FHS, which includes a number of different adverse reactions to foods, including food allergy [
5]. Food allergy is rarely associated with mortality [
42] or daily physical food related symptoms, but the psychological stress of accidently being exposed to the culprit food can be a burden [
6,
43]. Many children with FHS do not seek health care due to mild symptoms to foods [
44]. Thus, it is likely that those who seek health care due to FHS have more severe symptoms and/or experience a higher impact on their daily life compared to those who do not [
45]. This could explain the differing results in HRQL between hospital- based and our population-based study.
In analyses stratified by sex, we found no statistically significant differences in HRQL, except in the domain Social Acceptance and Bullying. In this domain, HRQL was more impaired among girls with FHS compared to girls without FHS, but this difference was not found among boys. It has been shown that adolescent girls generally experience a poorer HRQL compared to boys [
46] which is in line with our results. Even though FHS is common among children, it may affect social life and create social exclusion [
36] which may lead to bullying. In a previous study, children reported that they had been bullied because of their food allergy, mainly by classmates but also by teachers and school staff [
34].
The clinical Minimal Important Difference of the disease specific FAQLQ is not yet decided [
29]. We defined poor disease specific HRQL as ≥75th percentile and it was most common among children with current food allergy. A possible explanation is that severe symptoms are most common in this phenotype. While respiratory, cardiovascular and severe skin- and gastrointestinal symptoms are relatively common in food allergy [
21,
41], lactose intolerance present with milder bowel symptoms [
47]. Thus, children with current food allergy are probably more afraid of food reactions compared to children with other phenotypes of FHS associated with milder symptoms.
Interestingly, poor HRQL was also found among children with
outgrown food allergy. This was however not surprising since these children had a convincing history of food allergy, but they still avoided the culprit food despite tolerance had been achieved [
21]. It is well known that tolerance development is common in allergies to foods like egg and milk [
48], but children may remain on an elimination diet even if tolerance is achieved [
49]. Among our children with FHS, lactose intolerance was the most common phenotype, and these children also reported total elimination to cow’s milk [
21]. Studies indicate that adolescents with lactose intolerance can drink smaller amounts of cow’s milk without symptoms [
50]. Hence, after participating in our research program some of the children with FHS could reintroduce the eliminated food, partially or completely [
21,
51] which may improve their HRQL. Reasons for staying on a restricted diet are fear of food reactions, difficulties to tolerate taste and textures of the eliminated food and unwillingness to change an approach to food that has become normality [
51,
52]. Since reported FHS is common in the population [
3,
35] a correct diagnosis and follow-ups is important in order to evaluate persistence of FHS. This evaluation could be performed within the school health care in early school age [
53].
Strengths and limitations
The strength of our study is that we compared HRQL between children with and without FHS in the same large population-based cohort and by using both generic and disease-specific HRQL questionnaires. By using generic HRQL questionnaire it was possible to compare HRQL among children with FHS and without FHS [
54]. Because the classification of children into different FHS phenotypes was performed after completion of the HRQL questionnaire, the children’s responses were not affected by receiving a new diagnosis. Another strength is that the children answered the HRQL questionnaire themselves, since disagreement between child and parent-proxy have been reported [
55]. A limitation is that the disease specific questionnaire FAQLQ-TF is primarily developed for IgE-mediated food allergy [
13] and does not cover other subgroups of FHS. The Swedish FAQLQ-TF version has not yet been validated but has been used in a previous Swedish study [
28]. Regardless, FAQLQ-TF was used in our study because, to our knowledge, there is no available questionnaire in Swedish that is designed to describe adolescents’ own perspective of living with FHS. Despite the current study was based on a large population-based cohort with extremely high participation rate, we were lacking power for some analyses. Regarding the disease-specific HRQL, we found trends with those having current food allergy reporting the lowest HRQL although the differences did not reach statistical significance. Furthermore, the sample size did not allow analyses of HRQL in relation to number of foods avoided.
Authors’ contributions
ÅS, ER, VL, LH and AW contributed to the study design. ÅS, AW, ER, VL S-AJ and LH contributed to the analysis and interpretation of data. All authors were involved in the discussions and contributed to writing the manuscript. All authors read and approved the final manuscript.