Does birth order affect asthma risk?

Asthma :: Does birth order affect asthma risk?

A recent study challenges an old theory known as the ?hygiene hypothesis,? which suggests that older children protect their younger siblings from developing asthma.

To test this theory, researchers from Israel gathered and reviewed the medical records of 531,116 military draftees and assessed the prevalence of asthma in both the number of children per family and the birth order.

Results showed that asthma prevalence was inversely related to the number of children in a family but only in families of four or more children. Also, birth order had no effect on asthma prevalence. Researchers concluded that these results conflict with the ?hygiene hypothesis.?

This study appears in the June issue of CHEST, the peer-reviewed journal of the American College of Chest Physicians.