Incidence and risk factors for food hypersensitivity in UK infants: results from a birth cohort study

Food hypersensitivity continues to be a concern for health care professionals and the general population since it adversely affects quality of life [1, 2] and household and healthcare expenditure [3, 4]. Any public health concern needs local incidence and prevalence data [5] and this is particularly relevant for food hypersensitivity due to conflicting opinions as to prevalence [6, 7]. There is also great interest in its potential risk factors due to its association with the development of other conditions [8, 9]. Since geographical issues are also important in the development of food hypersensitivity, not all previously identified risk factors may be associated with food hypersensitivity development in a UK cohort in infants. One study has looked at risk factors of food hypersensitivity development in the UK but it only considered dietary factors [10]. We have previously described the relationship between breast feeding, complementary feeding and dietary patterns and food hypersensitivity in this cohort. In this publication we now present data on the incidence of food allergy in the UK within a general UK cohort and describes the results of a follow up of 1140 infants pairs. In an additional exploratory analysis, we also aimed to investigate the possible risk factors for IgE and non-IgE mediated food allergy.

In this UK cohort we found the cumulative incidence of DBPCFC confirmed food hypersensitivity to be 5.0 % (3.7–6.7). This is a little higher than other published figures of 0.0–4.2 % in the 0–5 year age group [5]. This is probably due to methodological differences since many studies only performed DBPCFC if there was sensitisation thus potentially missing non-IgE-mediated food hypersensitivity. The observed difference may also be due to geographical differences since it is thought the incidence of food hypersensitivity reactions is higher in Northern European countries [5].

Since all children with a clinical history of food hypersensitivity were challenged in this study, a cumulative incidence for both IgE- and non-IgE-mediated conditions could be determined: 2.6 % (1.5–3.6) for IgE-mediated food allergy and 2.4 % (1.4–3.5) for non-IgE-mediated food hypersensitivity. There is a lack of published data for non-IgE-mediated food hypersensitivity for comparison, but our results are broadly similar to those published in the most recent systematic review [17] although they are somewhat higher for hens’ egg (2.1 % compared to 0.0–1.7 %).

Novel to this study was the ability to look at risk factors for differing phenotypes of food hypersensitivity. Our exploratory analysis showed the factors associated with food hypersensitivity were wheeze, maternal atopy, gestation, age at first solids and healthy eating dietary pattern, which are similar to those found in previous research [18‐25]. For IgE-mediated disease, the multivariable analysis demonstrated eczema, rhinitis and healthy eating pattern to be significant independent risk factors. The association between eczema and food allergy has long been recognised [26] and the opinion that eczema is a likely risk factor for food allergy is becoming more widely accepted due to data relating filaggrin gene defects with the development of eczema, allergic sensitization, and asthma and allergic rhinitis [27‐29]. Filaggrin gene defect leads to a damaged skin barrier which increases permeability to exogenous proteins and possibly exposure of the innate immune system to allergens [30]. This phenomenon may also account for rhinitis being a risk factor for food allergy since the infant may also have become sensitised to aeroallergens through a damaged epithelial layer [31]. A healthy eating pattern was identified as being protective against the development of food allergy with the possible mechanism being the immunomodulatory effect of nutrients found in fruit and vegetables which were a feature of the observed healthy eating pattern along with a predominantly home-cooked diet [13]. Fruit and vegetables are good sources of vitamin C, beta-carotenes, folate and oligo-saccharides all of which have been shown to have immunomodulatory actions [32‐34]. Also, home processed foods may have a higher microbial load than commercially prepared foods [35] and this may offer protection from the development of allergic disease as suggested by the “Hygiene Hypothesis” [36].

In the multivariable analysis for infants with non-IgE-mediated food hypersensitivity, dog in the home, healthy eating pattern, probiotic whilst breastfeeding and younger age at first solid food introduction were independent risk factors. The nature of the relationship between pet ownership and allergy development is still under debate [37‐40]. If a protective effect is only seen for IgE-mediated conditions then that may explain the conflicting findings in the literature. It is recognised that pet ownership results in altered household microbial communities [41] and that these differences can lead to altered gut flora [42]. Whilst this may lead to changes in the immune system which reduce the risk of IgE-mediated allergy [43] this altered gut flora can adversely affect digestive enzyme activity, particularly of lactase. This is a previously reported phenomenon [44] and since the majority of infants with non-IgE-mediated food hypersensitivity were reactive to milk, this is a potential mechanism for these cases.

The effect of altered gut microbiota may also be the reason for other observed associations in these infants including healthy eating pattern and probiotic consumption during breastfeeding. The healthy eating dietary pattern may have a protective effect on gut health since it contained large amounts of home processed fruits and vegetables which are good sources of oligo-saccharides which, as naturally occurring prebiotics, promote gut colonization by bifidobacterium [45]. The observed association between probiotic consumption during breastfeeding and non-IgE-mediated food hypersensitivity is not readily explained but it can be hypothesised that it relates to the effect of the infant gut flora on gut enzyme activity. There is evidence that probiotics taken when breastfeeding alter breast milk composition [46] and that this may reduce the risk of allergy development in the infant [47]. However, there is no data describing the effect of maternal consumption of probiotic during lactation on the infant gut flora but it could be hypothesised that it increases the bifidobacteria colonisation that has been reported during breastfeeding [48] thus enhancing the effect of the breast milk on gut flora further. At breastfeeding cessation the infant’s gut flora becomes predominantly populated by coliform and bacteroid bacteria [48] which do not aid gut enzyme activity like hybridisable bacteria does [49] so the sudden change in the gut enzyme promoting environment may cause the observed Non-IgE mediated symptoms.

The age at first solid food introduction was significantly different for food hypersensitivity and for non-IgE-mediated food hypersensitivity. This observation could explain why some previous studies found an association between the early introduction of solids and food hypersensitivity [23, 24] and others have not [50, 51] since most studies do not identify the phenotype of hypersensitivity being investigated. It is considered that the infant gut is relatively immature before age 4–6 months and introducing solids before this time could cause food hypersensitivity symptoms, due to physiological mechanisms such as high intestinal permeability [52] which could upset the normal homeostasis of mucosal cell transport processes [53].

The strengths of this analysis include a large cohort of 1140 infants at general risk of developing food hypersensitivity with good follow-up to 24 months and a diagnosis using the gold standard methodology of a DBPCFC. Additionally, the methodology allowed for the prospective identification and clinical assessment of infants reacting to foods which reduced the likelihood of tolerance developing before a diagnosis could be confirmed. The prospective design also reduced the likelihood of recall bias during data collection and the prospective collection of food diary data is unique in a cohort of this size. Limitations of our analysis are that the study population is not fully representative of the population from which it was recruited since our mothers are older (Fig. 3). Also, the control infants were 5 months older than the cases as they were matched by birth but recruited after the cases were assessed; since control infants had never had any adverse reactions to food we do not expect this difference to impact on any of the factors included in the risk factor analyses. Additional limitations are that the numbers of infants diagnosed as reactive to foods were too small to enable all the likely risk factors to be detected, or to allow us to look at individual food reactions to determine whether different foods behave differently and have different risk factors associated with them. Also, despite the prospective nature of the study, reverse causality could not be completely avoided as clinical symptoms can lead to treatments which are subsequently associated with the condition in an analysis, as was the case for anti-reflux medication. Furthermore, a diagnosis of allergy can result in a change of behaviour as was the case for when mothers first introduced egg into the diet. However, where there was a suspicion of reverse causality, the variable was not included in the final multivariable analysis thus reducing its effect on the final study findings. Finally, the risk factor investigation represents an exploratory analysis and needs to be replicated, since possible regional differences within the UK may mean the findings from this study are not necessarily nationally representative.

This study presents unique data from the UK on both IgE-mediated food allergy and non IgE-mediated food hypersensitivity in early childhood. It found the cumulative incidence of DBPCFC confirmed food hypersensitivity to be 5.0 % (3.7–6.7). Our results also suggest that different factors may affect the development of IgE-mediated and non-IgE-mediated reactions to food in infants and young children. However, it is important that this exploratory analysis is confirmed in other cohorts. Analysis of the EuroPrevall data from all the birth cohort centres for all food reactions can build upon this work and also investigate any geographical differences to food hypersensitivity reactions.