Overweight/obesity and risk of seasonal asthma exacerbations.

BACKGROUND: Obesity is associated with an increased risk for asthma exacerbations, but whether this risk is related to the season of exacerbation is not known.

OBJECTIVE: To determine the relationship of increased body mass index (BMI) to the season of asthma exacerbation.

METHODS: Study subjects were adult (aged 18-65 years) and children (aged 5-17 years) health plan members with persistent asthma in 2008 for whom a BMI measurement was available. BMI categories were normal (<25 kg/m(2)), overweight (25-29.9 kg/m(2)), and obese (≥30 kg/m(2)). Exacerbations were defined as oral corticosteroid dispensings linked to an asthma encounter in the spring, summer, fall, or winter of 2009.

RESULTS: The cohort included 17,316 adults and 10,700 children. There was a significant (P < .05) linear increase with BMI category in the proportion of adults with exacerbations in every season and in the proportion of children with exacerbations during fall and winter. Relationships of overweight or obesity (vs normal weight) to fall and winter exacerbations remained significant in both adults and children after adjustment for sex and education. In a generalized estimating equation model, both BMI status and season (spring, fall, and winter) were related to exacerbations. Moreover, we noted a significant interaction in adults (P = .03) but not children (P = .97) of the BMI-exacerbation association by season (fall-winter vs spring-summer).

CONCLUSION: Higher BMI values increased the risk for asthma exacerbations in adults and children with persistent asthma, particularly for fall-winter exacerbations in adults. Potential mechanisms for these findings, including vitamin D status, viral infections, and corticosteroid responsiveness, merit further study.