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

Abstract

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 (β = 0.006 l, 95% CI (0.001 to 0.01)) and forced vital capacity (FVC) (β = 0.012 l, 95% CI (0.007 to 0.017)). However, decrements in the FEV₁/FVC ratio were noted with increasing BMI (β = −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.