Relation between body composition, abdominal obesity, and lung function

Reference values of spirometry and diffusion capacity are usually adjusted for age, sex, height and ethnic origin. However, also other factors, mainly weight and body composition, have an effect on pulmonary function. Therefore, we examined how body composition and abdominal obesity are related to lung function in normal population and whether they should be taken into account in the reference values. Two hundred and eighty-four healthy Finnish non-smoking adults were included in the study. Height, waist circumference, abdominal sagittal diameter and body composition were measured, and spirometry and diffusion capacity (DLCO) were performed. Muscle mass (r = 0.29, P = 0.000) and lean body mass (r = 0.29, P = 0.000) correlated positively with DLCO. However, no significant correlation between body composition and spirometry results was observed. Abdominal sagittal diameter (r = -0.21, P = 0.000) and waist circumference (r = -0.22, P = 0.000) correlated inversely with the forced expiratory volume in 1 s/forced vital capacity ratio (FEV1/FVC). In our study population, subjects with higher muscle and lean body mass had higher DLCO. This indicates a need for future re-evaluation of reference values. Besides, already minor abdominal obesity is associated with obstructive changes in spirometry results.