Obesity and chronic obstructive pulmonary disease: Is fatter really better?

BACKGROUND: Overweight/obesity is associated with longer survival in chronically ill patients, a phenomenon referred to as the 'obesity paradox'. OBJECTIVE: To investigate whether the obesity paradox in patients with chronic obstructive pulmonary disease (COPD) is due to fat accumulation or confounding factors. METHODS: A total of 190 patients with stable COPD who underwent a mean (+/- SD) follow-up period of 72 +/- 34 months were enrolled. Anthropometry, pulmonary function tests, midthigh muscle cross-sectional area obtained using computed tomography (MTCSA(CT)), arterial blood gas and exercise testing data were measured at baseline. Patients were categorized into two subgroups according to body mass index (BMI) <25 kg/m(2) or >= 25 kg/m(2) (normal and overweight/obese, respectively). RESULTS: Seventy-two patients (38%) died during the follow-up period. Survival tended to be better in the overweight/obese patients but this difference did not reach statistical significance. Overweight/obese patients had better lung function and a larger MTCSA(CT) than those with normal BMI (P<0.001). Overweight/obese patients also had a significantly higher peak work rate than patients with normal BMI (P<0.001). PaO2 and PaCO2 were not significantly different in the two groups. When adjusted for PaCO2, peak work rate and MTCSA(CT), the tendency for improved survival in overweight/obese patients disappeared. In fact, when these variables were considered in the survival analysis, patients with lower BMI tended to have better survival. CONCLUSION: These results suggest that important confounders, such as hypercapnia, exercise capacity and muscle mass, should be considered when interpreting the association between increased BMI and survival in patients with COPD.