Food allergy (FA) in childhood has been shown to be more prevalent in those born in autumn and winter. The mechanisms of this season-of-birth effect remain unclear, although shortage of vitamin D during infancy has been considered one possible mechanism. The purpose of this study was to investigate the effect of eczema on the season-of-birth effect on FA in infancy.
A questionnaire survey on the prevalence of allergic diseases was completed by the parents of 14 669 Japanese schoolchildren, aged 7–15 years, in Kyoto City, Japan. Logistic regression models were constructed to compare the prevalence of FA in infancy according to season of birth.
Those born in autumn and winter had a significantly higher prevalence of FA in infancy compared to those born in spring and summer in a multivariate model (4.8% vs 3.6%, P = 0.001). The difference, however, was no longer significant when eczema before 6 months was included as either an additional or only confounding factor. The difference among those with and without eczema before 6 months was further analyzed, and it was found that, in both groups, there was no difference between those born in spring and summer and those born in autumn and winter.
The season-of-birth effect on FA in infancy was significantly affected by the existence of eczema before 6 months in Japanese children. Eczema before 6 months may be the factor directly related to the season-of-birth effect on FA in infancy.