A child's likelihood of developing food allergies can be traced back to the season during which he or she completes their first three months of life in the womb, suggests research published online in the Journal of Epidemiology and Community Health.
The Finnish researchers base their findings on just under 6000 children, all of whom were born between 2001 and 2006 and lived in one area of Finland.
Out of the total, just under 1000 were tested for sensitisation to food allergens between the ages of 0 and 4 years, with the likelihood of a positive test result rising sharply during the first year of life.
Up to the age of 4, the incidence of an allergic response to certain foods varied according to season of birth, ranging from 5% for children born in June/July to 9.5% for those born in October/November.
Around one in 10 (11%) children, whose 11th week of development in the womb had occurred during April or May were sensitised to food allergens. This compared with a rate of 6% among children who reached that stage of fetal development in December/January.
Readings of ambient pollen for the years in question showed that levels of birch and alder pollen peaked during April and May.
When narrowed down to specific allergens, the results indicated that a child whose first three months of fetal development ended in April or May was three times more likely to be sensitised to milk and eggs than those who reached this stage of development in November or December.
Research already indicates that children born in autumn or winter are more prone to eczema and wheeze, and that they have higher levels of circulating antibodies to allergens than children born in spring or summer, say the authors.
This might be because the fetus begins to produce antibodies to allergens at around the 11th week of development, and antibodies to specific allergens by around 24 weeks, they suggest.
An allergic type response is thought to be necessary for the pregnancy to continue, and in some cases this persists after birth. But the timing of the development of sensitisation has been the subject of heated debate.
Materials provided by BMJ-British Medical Journal. Note: Content may be edited for style and length.
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