Association of body mass index with mortality in COPD through exacerbations and cardiovascular events

The mechanisms through which body mass index (BMI) influences the prognosis of chronic obstructive pulmonary disease (COPD) remain poorly understood. This study investigates whether BMI influences all-cause mortality in patients with COPD through mediating effects of exacerbations and cardiovascular events.

Data were obtained from a multicentre prospective COPD cohort (NCT02800499). BMI was assessed both continuously and categorically as <23 (low), 23-27 (normal) and >27 kg/m² (high). The primary outcome was all-cause mortality and secondary outcomes were moderate-to-severe exacerbations and cardiovascular events. Mediation analyses were applied to quantify the contribution of these events to the association between BMI and all-cause mortality.

Among 3314 patients with COPD, those with low BMI had a higher risk of mortality (adjusted OR, 1.46; 95% CI 1.04 to 2.07), whereas no significant difference was observed among those with high BMI. Mediation analyses indicated that exacerbations partially mediated the relationship between BMI and all-cause mortality, explaining 11.9% of the increased mortality among patients with low BMI and 21.9% of the reduced mortality among those with high BMI. Meanwhile, cardiovascular events showed mediating effects in the opposite direction, contributing to 5.2% lower mortality among patients with low BMI and 11.5% higher mortality among those with high BMI.

BMI was non-linearly associated with all-cause mortality in COPD. Exacerbations mediated the excess mortality risk among patients with low BMI, whereas the decreasing risk of cardiovascular events in this group contributed to a countervailing effect that tempered the overall association between low BMI and mortality.