Does birth season influence the odds for asthma? Large cohort analysis

Background and Objective Few studies have examined the possibility of a link between birth season and the risk for asthma. Those studies that mainly focused on young children, reached different conclusions regarding both the existence of such a link and the season with the highest risk. The purpose of this study was to reinvestigate the relationship between birth season and asthma in a very large cohort, larger than in all previous studies, focusing on adolescents. Methods The medical records of consecutive 17‐year‐old conscripts, born between 1978 and 1999, undergoing medical evaluation before their military service, were reviewed. The prevalence of asthma among conscripts was calculated according to the season of birth. Results Data from 6 26 460 males and 4 54 104 females were collected. Asthma prevalence was 6.6% of the males and 5.8% of the females. Asthma prevalence was highest among those born in the summer and was approximately 9% higher in women and 6% higher in men than those born in the winter. Those born in the winter had the lowest prevalence of asthma. June was the birth month with the highest prevalence of asthma in both genders together with September among males. Conclusions Being born in the summer, especially in June, is associated with an increased risk of asthma compared with a winter birth among Israeli army conscripts. Further research is required to determine the impact of the season of birth on the risk of asthma in higher risk populations.