New data suggests smoking has a greater effect on BMI than first thought

The research, led by Carmen Amador at the University of Edinburgh, analysed genome sequence data from over 18,000 of our volunteers.

A close up of a man's hands holding a smoking cigarette

The research also included data from UK Biobank, allowing for research into over 390,000 British volunteers.

Amador and colleagues studied how tobacco smoking and genetics interact to influence Body Mass Index (BMI) and other obesity-related traits. They found that the amount people smoked, as reported by the individuals themselves, explained 2% of the variation in their BMI. Their genetics explained 50% of the variation between individuals. Interestingly, a further 10% of BMI was explained by the interaction between smoking status and genetics. This suggests that an individual's genetics affects the impact that smoking has on their BMI.

Researchers also found that a person's sex played an important role. The interaction between genetics and smoking explained more of the variation in traits, such as weight and body fat percentage, in men than in women.

BMI is known to be strongly affected by genetics, but the effects of a person's environment are less well understood. To help understand the environmental effects, the researchers repeated their analysis on a sub group of 8,821 Generation Scotland volunteers. They used DNA methylation data as a measure of tobacco exposure.

DNA methylation is a mechanism involving the addition of a methyl group (one carbon atom and 3 hydrogen atoms) to specific regions in the DNA, which may change how a gene works and is expressed. The level of DNA methylation at particular points in the DNA may be altered by a person's environment or lifestyle, such as what a person eats or where they live.

In this case, the researchers found that the methylation status at 62 sites, which had previously been linked to smoking, was able to explain 22% of the variation in BMI between individuals. This means DNA methylation patterns linked to smoking explain ten times more variance than the level of smoking that individuals report.

The authors say that DNA methylation may be a more accurate measure for some environmental factors than self-reported data. It could be used to investigate the influence of other difficult-to-measure lifestyle differences on diseases like obesity.  

Our study highlights the potential of using biomarkers as a measure of an individual's past environment and lifestyle and also suggests that the environment we experience may have long-term effects by altering the way our genetic makeup influences our health and related traits.

Carmen Amador
MRC Human Genetics Unit, University of Edinburgh

 This research was published in PLOS Genetics. To read the full paper visit the link below.

Genome-wide methylation data improves dissection of the effect of smoking on body mass index