Commentary: Tobacco consumption and body weight: Mendelian randomization across a range of exposure

Tobacco consumption is consistently associated with reduced body weight, creating an incentive to initiate smoking and a disincentive to cease, although the health risks associated with the habit outweigh the benefits of reduced weight. Among smokers however, increasing con-sumption has been associated with increased body weight. To determine whether this contradiction reflects causal processes, Winsløw et al.1 have applied Mendelian ran-domization (MR) in testing the association of a genetic variant, rs1051730 in CHRNA3, with measures of body weight among 80 342 members of the Copenhagen General Population Study. Among smokers, each minor (T) allele carried was associated with an increase of about one cigarette per day, but with a decrease in several meas-ures of body weight, in contrast to the observational re