Relationship between obesity, body composition, and pulmonary function among Korean adults aged 40 years and older

Pulmonary function is influenced by factors such as age, sex, height, and weight. This study investigated the relationship between obesity, body composition, and pulmonary function measures (forced expiratory volume in one second [FEV₁], forced vital capacity [FVC], and the FEV₁-to-FVC ratio) of Korean adults aged 40 years and older. Using the fifth Korea national health and nutrition examination survey in 2010 and 2011, multiple regression analyses were performed to identify factors associated with pulmonary function, stratified by sex. Independent variables were waist circumference (WC) and an additional measure of obesity/muscularity (weight in model 1, body mass index [BMI] in model 2, and fat-free mass index [FFMI] in model 3). Among 3918 adults, the mean FFMI was 17.7 and 15.0 kg/m² for men and women, respectively. Weight and BMI were positively associated with only FEV₁ (B = 0.003 and B = 0.006, respectively, p < 0.01) and the FEV₁-to-FVC ratio (B = 0.001, p < 0.01) in women. FFMI was positively associated with FEV₁ and FVC in both sexes (B = 0.019, p < 0.05 for FEV₁ and B = 0.020, p < 0.01 for FVC in men; B = 0.025, p < 0.0001 for FEV₁ and B = 0.022, p < 0.0001 for FVC in women). WC was inversely associated with FEV₁ and FVC in men and FEV₁ in women, respectively. Weight and BMI behaved as indicators of body size based on their positive associations with pulmonary function. In conclusion, FFMI can be an important and consistent predictor of pulmonary function in both men and women.