Effects on body mass index of gene linked to heavy smoking

Press release issued: 4 December 2014 A genetic variant which causes smokers to smoke more heavily has been shown to be associated with increased body mass index (BMI) - but only in those who have never smoked, according to new research led by the University of Bristol, UK and published today in PLOS Genetics. It is likely that this finding has not come to light before because it has been masked by the effect of smoking, which acts to reduce BMI. Professor Marcus Munafo from Bristol's School of Experimental Psychology and colleagues studied a variant in the CHRNA5-A3-B4 gene cluster which is known to increase smoking heaviness. They found that the variant is associated with lower BMI in current smokers, but higher in people who have never smoked. This difference in effects suggests that the variant influences BMI in opposite directions - via pathways other than smoking for those who have never smoked and by increasing the weight-reducing effects of smoking in those who smoke. The reason for this association with BMI in never smokers is not yet understood. It is known that this genetic variant alters response to nicotine, which is why it affects the number of cigarettes that an individual smokes.