Association of body mass with pulmonary function in the Childhood Asthma Management Program (CAMP)

Background: While increases in body mass index (BMI) have been associated with the incidence and prevalence of asthma, the mechanisms behind this association are unclear. Methods: We hypothesised that BMI would be independently associated with measures of asthma severity in a population of children with mild to moderate asthma enrolled in the Childhood Asthma Management Program ( CAMP). A multivariable baseline cross sectional analysis of BMI with our outcomes of interest was performed. Results: BMI was generally not associated with symptoms, nor was it associated with atopy. While BMI was positively associated with the methacholine concentration that causes a 20% fall in forced expiratory volume in 1 second (PC20FEV1), this association did not persist after adjustment for FEV1. Increasing BMI was associated with increasing FEV1 (beta = 0.006 l, 95% CI (0.001 to 0.01)) and forced vital capacity ( FVC) (beta = 0.012 l, 95% CI (0.007 to 0.017)). However, decrements in the FEV1/FVC ratio were noted with increasing BMI (beta = -0.242, 95% CI (-0.118 to -0.366)). Thus, an increase in BMI of 5 units was associated with a decrease in FEV1/FVC of over 1%. Conclusions: Although the association of FEV1 and FVC with BMI did not support our initial hypothesis, the decrease noted in the FEV1/FVC ratio has potential relevance in the relationship between BMI and asthma severity.