Obesity in chronic obstructive pulmonary disease: is fatter really better?

Overweight⁄obesity is associated with longer survival in chronically ill patients, a phenomenon referred to as the 'obesity paradox'.

To investigate whether the obesity paradox in patients with chronic obstructive pulmonary disease (COPD) is due to fat accumulation or confounding factors.

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 (MTCSACT), 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⁄m2 or ≥25 kg⁄m2 (normal and overweight⁄obese, respectively).

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 MTCSACT 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 MTCSACT, 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.

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.