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

While increases in body mass index (BMI) have been associated with the incidence and prevalence of asthma, the mechanisms behind this association are unclear.

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.

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 (PC(20)FEV(1)), this association did not persist after adjustment for FEV(1). Increasing BMI was associated with increasing FEV(1) (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 FEV(1)/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 FEV(1)/FVC of over 1%.

Although the association of FEV(1) and FVC with BMI did not support our initial hypothesis, the decrease noted in the FEV(1)/FVC ratio has potential relevance in the relationship between BMI and asthma severity.