Role of obesity in smoking behaviour: Mendelian randomisation study in UK Biobank

OBJECTIVE: To determine whether body mass index, body fat percentage, and waist circumference influence smoking status and intensity. DESIGN: Mendelian randomisation study. SETTING: UK Biobank, with replication of results from the Tobacco and Genetics (TAG) consortium. PARTICIPANTS: European descent participants from the UK Biobank cohort (n=372 791) and the TAG consortium (n=74 035). MAIN OUTCOME MEASURES: Risk of current and past smoking, number of cigarettes smoked per day, age of smoking initiation. RESULTS: The Mendelian randomisation analysis indicated that each standard deviation increment in body mass index (4.6) increased the risk of being a smoker (odds ratio 1.18 (95% confidence interval 1.13 to 1.23), P<0.001). This association was replicated in the TAG consortium data (1.19 (1.06 to 1.33), P=0.003). Furthermore, each standard deviation increment in body mass index was estimated to increase smoking intensity by 0.88 cigarettes per day (95% confidence interval 0.50 to 1.26, P<0.001) in UK Biobank and 1.27 cigarettes per day in the TAG consortium (0.46 to 2.07, P=0.002). Similar results were also seen for body fat percentage and waist circumference in both UK Biobank and the TAG consortium data. CONCLUSIONS: These results strongly suggest that higher adiposity influences smoking behaviour and could have implications for the implementation of public health interventions aiming to reduce the prevalence of these important risk factors.