Obesity linked to increased propensity, frequency of smoking

Obesity linked to increased risk of taking up smoking and smoking frequency according to a study published in BMJ. Obesity is now recognized as one of the most important health hazards accounting for a large fraction of early deaths worldwide.

Robert Carreras Torres and his associates conducted a study to determine whether body mass index, body fat percentage, and waist circumference influence smoking status and intensity.

The study included 450,000 individuals from the UK Biobank database and the Tobacco and Genetics (TAG) consortium - using a technique called Mendelian randomization. An association that is observed using Mendelian randomization is therefore likely to reflect a causal relation.

Three measures of smoking behavior were assessed: current and past smoking, a number of cigarettes smoked per day, and age of smoking initiation. The average age of study participants was 58 years.

The results showed that each 4.6 kg/m2 increase in BMI was associated with an 18% increased risk of being a smoker in UK Biobank and a 19% increased risk in the TAG consortium data.Each increase in BMI was also estimated to increase smoking frequency by around one cigarette per day (0.88 in UK Biobank and 1.27 in the TAG consortium).

Similar results were seen for body fat percentage and waist circumference and were consistent in both men and women.

Obesity and tobacco smoking are important risk factors but their inter-relationship is complex. Observational studies consistently show an inverse relationship between current cigarette smoking and body weight, followed by weight gain after one stops smoking. The first relationship is thought that smoking reduces appetite, and the second may be a consequence of higher caloric intake due to the replacement of the smoking habit with food intake.

However, active smokers who smoke more intensively tend to weigh more than light smokers which may be due to other lifestyle factors, such as physical inactivity and unhealthy diet, it is also possible that obesity could influence smoking uptake and intensity.

The researchers said that several assumptions were made in the study and the possibility that sociodemographic factors may have influenced the results cannot be ignored.

The study was published in the BMJ