Body-mass index as a predictor of incident asthma in a prospective cohort of children.

An epidemic rise in asthma has occurred concurrently with a rise in overweight among United States children, but it is unclear whether body weight affects the risk of incident childhood asthma. We studied the prospective relation of body-mass index (BMI) to incident asthma in a longitudinal study of 9,828 children aged 6-14 years, examined annually over a median follow-up time of 5 years in six US cities. An increased risk of a new asthma diagnosis in girls was associated with higher BMI at entry into the study (P=0.009) and greater increase in BMI during follow-up (P=0.0003). Compared with girls in the leanest quintile of BMI at entry (age taken into account), girls in the top quintile of adiposity had 2.2 times greater risk of incident asthma with any wheeze in subsequent years. Girls with the largest annual rate of increase in BMI (top compared to bottom quintile, age taken into account) had 1.5 times the risk of asthma with any wheeze, and 2.2 times the risk of asthma with persistent wheeze. Boys with the largest and smallest annual changes in BMI also had an increased risk of asthma. For girls, overweight contributes to development of asthma. For boys and girls, extremes of annual BMI growth rates increase the risk of asthma.