Children's Birth Date Can Increase Their Risk for Asthma

Will the time of year when my child is born affect asthma risk?

In this entry, I would like to discuss some very recent research that has grabbed media attention: the effect of birth during the time of year on the development of asthma in infants. There has been a well-known association between viral infection (typically from cold viruses and related viruses) in infancy and the risk of developing asthma in childhood. Until now, we haven't known whether early viral infection contributes to the development of asthma or if young kids who will become asthmatic just get early viral infections more readily.

The current research suggests that viral infection in infancy (<1 year old) actually contributes to the development of asthma later in childhood.

Risks of developing asthma in infants
The study that was recently released looked at the time of year during which babies were born and the risk of developing asthma around ages 3-5. They were curious if being born 3-6 months before the peak winter virus season had any relationship to developing bronchiolitis (an infection of the smaller breathing tubes in the lung) and asthma. As expected, they found that timing of birth in relation to the winter peak viral time (4 months before almost to the day) was related to a higher rate of bronchiolitis. This confirms prior research that shows that the peak risk age for infants to get bronchiolitis is about 4 months of age.

However, they also found that babies born 4 months before the peak viral time had a 30% higher risk of developing asthma in childhood than kids born at different times of the year. This is the key finding: if asthma was associated with getting more bronchiolitis, there would be more infections in the kids that ended up getting asthma but no relationship between timing of birth and getting asthma. This concept is a little hard to grasp but quite compelling. And the study was not small - the researcher's studies 91,000 kids born over 5 years in Tennessee, so the conclusions are robust and backed by strong data.

We need to remember that (as mentioned in earlier entries) asthma is a disorder in which heredity (genes - who your parents are) and environment interact. Asthma (and allergies) is more common in the children of parents who have asthma. It does tend to run in families. But there are many children of asthmatic parents who never get asthma. This could be due to chance (which genes are passed on obviously varies from child to child) and environment. A ‘high risk' child may not develop asthma in an environment where there are few allergens, or may develop asthma symptoms after moving to a new city or house, for example. In this study, the investigators made sure that the effect they were seeing was not due to these other predictors of asthma. Using sophisticated statistical analyses, they were able to find that timing of birth during the year was at least as strong and perhaps a stronger factor in predicting the development of asthma in childhood.