The influence by body mass index on annual lung function decline is not related to smoking status

Abstract

Background: Smoke cessation is associated with a decrease in lung function decline compared to sustained smoking, yet it is also associated with weight gain. We hypothesized that increased body mass index (BMI) suppresses the beneficial effects by smoke cessation on lung function. Methods: In a longitudinal cohort of Norwegian aluminum industry workers, spirometry, BMI and smoking status were available in 4142 persons (mean age 29, 85% male). The influence by BMI changes on forced vital capacity (FVC), forced expiratory volume during 1 st second (FEV 1 ) and FEV 1 /FVC in relation to smoking cessation were assessed in linear mixed model analyses, adjusted for baseline age and gender. Results: The unadjusted annual increase (standard error) in BMI was 0.16 (0.01), 0.12 (0.01) and 0.12 (0.01) in never-smokers, quitters and sustained smokers, respectively. In the adjusted analyses , an increase in BMI was independently associated with higher annual decline in FEV 1 and FVC in all groups. Furthermore, an increase in BMI was associated with an increase in FEV 1 /FVC, independent of smoking status. Conclusion: Weight-gainers among smoke quitters have higher annual lung function decline, with a pattern towards restriction, but this effect was not different in never-smokers or sustained smokers.