Re: Body Mass Index and Risk of Lung Cancer Among Never, Former, and Current Smokers

Using a standardized series of dose– response cancer-specific meta-analyses, we previously reported positive associations between body mass index (BMI) and the risks of several cancers (1). Two smoking-related cancers, namely lung and esopha-geal squamous cell carcinoma, were notable exceptions: the risks of these cancers were inversely associated with BMI. Given the established observation that BMI values are generally lower in current smokers than in never smokers, we reasoned that the observed inverse associations reflected residual confounding by smoking. In a recent article in the Journal, Smith et al. (2) have comprehensively addressed this question in almost half a million individuals from the NIH AARP cohort. Among current smokers, they found an inverse association between BMI catego-ries and the risk of incident lung cancer both in men and women when only adjust-ing for age. The authors extended their age-adjusted models to control for detailed smoking status and dose, cigar or pipe smoking. This adjustment hardly changed the five hazard ratios and the 95 % confi-dence intervals when comparing different BMI categories with the 22.5–24.9 kg/m