Body mass index and asthma incidence in the Black Women's Health Study

Background: Evidence from prospective studies consistently links obesity to asthma onset in white women, although there is controversy as to whether the association is causal. There are few data on this topic in black women, among whom the prevalence of obesity and asthma is high. Objective: We prospectively assessed the relation of body mass index (BMI) to asthma incidence in the Black Women's Health Study. Methods: We followed 46,435 women from 1995 through 2005 with biennial mailed questionnaires. Cox regression models were used to estimate incidence rate ratios and 95% CIs. Results: During 403,394 person-years of follow-up, 1068 participants reported physician-diagnosed asthma and concurrent use of asthma medication. Compared with women with BMIs of 20 to 24, the multivariate incidence rate ratios for higher categories of BMI increased from 1.26 (95% CI, 1.05-1.5.1) for BMIs of 25 to 29 to 2.85 (95% CI, 2.19-3.72) for BMIs of 40 or greater, with a significant trend. The association of BMI with asthma risk was consistent across strata of smoking status, age, presence of sleep apnea, parental history of asthma, BMI at age 18 years, and energy expenditure and intake. Conclusion: In this large cohort of African American women, there was a positive association between BMI and asthma risk that was similar in magnitude to those observed in longitudinal studies of white women. (J Allergy Clin Immunol 2009;123:89-95.)