According to Dr. Paul Brennan from IARC, the International Agency for Research on Cancer, around 70 genes have been identified for the first time that could explain this behaviour. IARC is a World Health Organization (WHO) agency, mandated to conduct research on the causes of cancer, and its prevention.

The study, which is being published on Thursday in the British Medical Journal, and funded by Cancer Research UK, found that increased body mass index (BMI), body fat percentage and even waist circumference, were associated with “a higher risk of being a smoker, and with greater smoking intensity, measured by the number of cigarettes smoked per day”.

“Based on genetic markers of obesity, the study allows us to better understand the complex relationship between obesity and important smoking habits,” said Dr. Brennan, a genetic epidemiology expert with IARC, and one of the authors of the study.

He added that the study showing the relationship between body mass and smoking, also suggested that there was possibly a “common biological basis for addictive behaviours, such as nicotine addiction and higher energy intake”.

Dr. Brennan also noted that in understanding the link better, it could also be useful as a tool in helping people to stop smoking — a habit that kills more than 7 million people each year, according to WHO.

It is well established that smokers have a lower body weight on average than non-smokers, possibly due to reduced appetite, but that many gain weight after they stop smoking.

“However, among smokers, those who smoke more intensively, tend to weigh more,” said IARC.

IARC Director, Dr. Christopher Wild, said that “prevention of smoking is key to reducing the global burden of cancer and other chronic diseases, such as cardiovascular disease and diabetes”.

He added that obesity was among the most important preventable causes of those chronic illnesses. “These new results provide intriguing insights into the potential benefits of jointly addressing these risk factors.”

Image: World Bank