Rationale: It is hypothesized that the metabolic syndrome explains the association between body mass index (BMI) and asthma in adults.
Objectives: Our objective was to longitudinally compare the relative strengths of the associations of the metabolic syndrome and BMI with incident asthma in adults.
Methods: We included 4,619 eligible participants in the Coronary Artery Risk Development in Young Adults (CARDIA) cohort followed over 25 years. Incident asthma was defined by a new self-reported provider asthma diagnosis plus either the presence of asthma symptoms and/or use of asthma medications. Cox proportional hazard analyses were performed.
Measurements and main results: Six hundred two subjects (417 women and 185 men) developed incident asthma over 25 years of follow-up. Metabolic syndrome predicted incident asthma among women but not men (unadjusted hazard ratios, 1.50 and 0.98; P = 0.01 and 0.93, respectively). BMI had a similar predictive association among women but not men (unadjusted hazard ratios, 1.19 and 1.04 per 5 units of BMI; P < 0.001 and 0.60, respectively). The association of metabolic syndrome with incident asthma in women was no longer statistically significant after adjustment for BMI (P = 0.44). In contrast, the association of BMI with incident asthma in women remained statistically significant after adjusting for the metabolic syndrome (P = 0.01). In a stepwise model, BMI was a stronger predictor than the metabolic syndrome (P = 0.001).
Conclusions: BMI is a stronger predictor of incident asthma among women than the metabolic syndrome. Other obesity-associated factors that are not a part of the metabolic syndrome may play a role in the BMI-asthma association in women.