Weight gain after smoking cessation does not modify its protective effect on myocardial infarction and stroke: evidence from a cohort study of men

Aims This study aimed to investigate the association between smoking cessation, post-cessation body mass index (BMI) change and risk of myocardial infarction (MI) and stroke in men. Methods and results A prospective cohort study using the National Health Insurance Service (NHIS) data set collected from 2002 to 2013 was implemented. Based on the first (2002-03) and second (2004-05) NHIS health check-up periods, 108 242 men aged over 40 years without previous diagnoses of MI or stroke were grouped into sustained smokers, quitters with BMI gain, quitters without BMI change, quitters with BMI loss, and non-smokers. Body mass index change was defined as the difference of more than 1.0 kg/m(2) between the two health check-up periods. The participants were followed-up from 1 January 2006 to 31 December 2013. Hazard ratios (HRs) and 95% confidence intervals (HR, 95% CI) were computed using Cox proportional hazard models adjusted for sociodemographic, health status, and family health history. Compared to the sustained smokers, the risk of MI and stroke was significantly reduced in both quitters with BMI gain (HR 0.33; 95% CI 0.16-0.70 for MI and HR 0.75; 95% CI 0.57-1.00 for stroke) and without BMI change (HR 0.55; 95% CI 0.37-0.83 for MI and HR 0.75; 95% CI 0.62-0.92 for stroke), but no significant association was found in quitters with BMI loss (HR 0.91; 95% CI 0.43-1.91 for MI and HR 0.86; 95% CI 0.57-1.31 for stroke), respectively. Non-smokers had lower risk of MI (HR 0.37; 95% CI 0.32-0.43) and stroke (HR 0.68; 95% CI 0.64-0.73) compared to the sustained smokers. Conclusion Post-cessation BMI change did not significantly modify the protective association of smoking cessation with MI and stroke.