Body mass index and smoking-related lung cancer risk in the Singapore Chinese Health Study

BACKGROUND: Smokers with low body mass index (BMI) may be more susceptible to lung cancer. METHODS: We prospectively examined the association between baseline BMI and lung cancer risk in the Singapore Chinese Health Study, a cohort of 63 257 Chinese enrolled between 1993 and 1998. RESULTS: After adjustment for smoking intensity and duration, BMI was inversely associated with risk of lung cancer among current smokers (P for trend=0.0004). Current smokers at different dosage of smoking with low BMI had significantly higher risk for lung cancer than those with high BMI. Hazard ratios (95% confidence intervals) of lung cancer for heavy smokers with BMI of > or =28, 24-<28, 20-<24, and <20 kg m(-2) were 6.37 (2.10-19.30), 9.01 (5.04-16.10), 8.53 (6.35-11.5), and 11.12 (6.60-18.70), respectively, as compared with nonsmokers. BMI had no modifying effects on lung cancer risk among nonsmokers and former smokers. CONCLUSION: Smokers with lower BMI may experience an enhanced risk of lung cancer. The findings have significant public-health implication given the increase in smoking prevalence in developing countries, where people still have relatively low BMI.