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 (FEV(1)) 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 FEV(1) 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/m(2) reduced FEV(1) 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 FEV(1) decline: an increase of baseline BMI by 1 kg/m(2) reduced FEV(1) 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 FEV(1) in male patients whereas this association was minimal in females patients. This gender-specific BMI effect was independent of COPD severity and smoking status.