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30-04-2012 | Immunology | Article

Fall birth increases food allergy risk


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MedWire News: Children born in fall (autumn) are up to twice as likely as those born during other seasons to develop food allergies, US study data show.

The findings, published in Allergy, revealed that the association was greatest among Caucasians and individuals with a history of eczema.

"Season of birth has been reported as a risk factor for food allergy, but the mechanisms by which it acts are unknown," say Corinne Keet (Johns Hopkins University, Baltimore, Maryland) and co-authors.

"It has been assumed that relative vitamin D deficiency mediates this relationship, although this has not been specifically confirmed," they add.

The team studied two populations of children: 5862 children from the National Health and Nutrition Examination Survey (NHANES) III and 1514 well-characterized food-allergic children from the Johns Hopkins Pediatric Allergy Clinic (JHPAC).

Food allergy was defined as self-report of an acute reaction to a food in NHANES, or as milk, egg, and peanut allergy in JHPAC.

The researchers report that an estimated 7% of the NHANES population had a history of a reaction to a food. These children were significantly more likely to be born in fall (September, October, or November) than in other seasons (odds ratio [OR]=1.91).

Furthermore, the relationship was significantly modified by ethnicity; fall birth was a risk factor for food allergy only among Caucasians, at an odds ratio (OR) of 2.34. There was no significant association between season of birth and food allergy among non-Caucasians.

The researchers say this finding is consistent with the theory that vitamin D is a mediator of the seasonal distribution of food allergy because Caucasians have more seasonal variation in vitamin D than darker-skinned populations.

However, they caution that other explanations, such as an increased genetic susceptibility among Caucasians and the joint influence of other environmental differences between these populations, cannot be excluded.

In the JHPAC cohort, the children were 1.31 times more likely to have been born in fall compared with the rest of the year.

In this group, fall birth was a risk factor for food allergy only among those with a history of eczema (OR=1.47).

This suggests that "sun exposure in early life may protect against skin inflammation, thereby protecting against food allergy during a critical period in development," Keet and co-authors remark.

Of note, neither history of doctor-diagnosed asthma nor allergic rhinitis was associated with fall birth, although each disease had its own distinct seasonal trend. Asthma was significantly less common among those born in the spring, while allergic rhinitis tended to be more common among those born in the spring, compared with the rest of the year.

By Laura Cowen

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