Gender modifies the effect of body mass index on lung function decline in mild-to-moderate COPD patients: a pooled analysis.

BACKGROUND: Low body weight is associated with poor prognosis in patients with chronic obstructive pulmonary disease (COPD). However, it is not known whether gender modifies this relationship. METHODS: We pooled data of 8686 COPD patients from 7 studies with a median length of 36-months of follow up. Using a longitudinal natural cubic spline regression model, we examined the dose-response relationship between body mass index (BMI) and the rate of decline in forced expiratory volume in one second (FEV1) in patients with GOLD 1 and 2 disease, stratified by gender and adjusted for age, smoking status, and cohort effects. RESULTS: There was an inverse linear relationship between BMI and the rate of FEV1 decline in GOLD Grades 1 and 2, which was modified by gender (p < 0.001). In male patients, an increase of BMI by 1 kg/m2 reduced FEV1 decline by 1.05 mL/year (95% CI 0.96, 1.14). However, in female patients, BMI status did not have a clinically meaningful impact on FEV1 decline: an increase of baseline BMI by 1 kg/m2 reduced FEV1 decline by 0.16 ml/year (95% CI 0.11, 0.21). These gender-modified relationships were similar between GOLD 1 and 2 patients, and between current and former smokers. CONCLUSION: In mild to moderate COPD, higher BMI was associated with a less rapid decline of FEV1 in male patients whereas this association was minimal in females patients. This gender-specific BMI effect was independent of COPD severity and smoking status.