Smoking cessation, but not reduction, reduces cardiovascular disease incidence

Aims The aim of this study was to assess the association of smoking cessation and reduction with risk of cardiovascular disease (CVD). Methods and results A total of 897975 current smokers aged >= 40years who had undergone two consecutive national health examinations (in 2009 and 2011) were included. Participants were classified as quitters (20.6%), reducers I (>= 50% reduction, 7.3%), reducers II (20-50% reduction, 11.6%), sustainers (45.7%), and increasers (>= 20% increase, 14.5%). During 5575556 person-years (PY) of follow-up, 17748 stroke (3.2/1000 PY) and 11271 myocardial infarction (MI) (2.0/1000 PY) events were identified. Quitters had significantly decreased risk of stroke [adjusted hazard ratio (aHR) 0.77 95% confidence interval (CI) 0.74-0.81; absolute risk reduction (ARR) -0.37, 95% CI -0.43 to -0.31] and MI (aHR 0.74, 95% CI 0.70-0.78; ARR -0.27, 95% CI -0.31 to -0.22) compared to sustainers after adjustment for demographic factors, comorbidities, and smoking status. The risk of stroke and MI incidence in reducers I (aHR 1.02, 95% CI 0.97-1.08 and aHR 0.99, 95% CI 0.92-1.06, respectively) and reducers II (aHR 1.00, 95% CI 0.95-1.05 and aHR 0.97, 95% CI 0.92-1.04, respectively) was not significantly different from the risk in sustainers. Further analysis with a subgroup who underwent a third examination (in 2013) showed that those who quit at the second examination but had starting smoking again by the third examination had 42-69% increased risk of CVD compared to sustained quitters. Conclusions Smoking cessation, but not reduction, was associated with reduced CVD risk. Our study emphasizes the importance of sustained quitting in terms of CVD risk reduction.