Background:
While smoking cessation reduces the risk of cardiovascular disease (CVD), quitting also increases fasting serum glucose (FSG) levels. The effect of post-cessation FSG elevation on cardiovascular disease is unknown.

Methods:
The study population consisted of 128,208 men without type 2 diabetes from the Korean National Health Insurance System - Health Screening Cohort database. Change in smoking habits and FSG was determined by the difference in smoking status and FSG levels from the first (2002 and 2003) and second (2004 and 2005) health examinations. Quitters were divided into those with FSG elevation of greater than 10.0 mg/dL and those without FSG elevation. The study participants were followed-up for cardiovascular disease and CVD-related death from 2006 to 2013.

Results:
Compared to continual smokers, quitters without FSG elevation had decreased risk of cardiovascular disease (hazard ratio, HR, 0.77, 95% confidence interval, CI, 0.69-0.86), while quitters with FSG elevation did not (HR 0.86, 95% CI 0.74-1.01). Similarly, quitters without FSG elevation had decreased risk of CVD-related death (HR 0.71, 95% CI 0.51-0.99) while quitters with FSG elevation did not (HR 0.86, 95 % CI 0.57-1.29). Both quitters with and without FSG elevation had decreased risk of myocardial infarction, while only quitters without FSG elevation had decreased risk of total stroke.

Conclusions:
Post-cessation FSG elevation attenuated the beneficiary risk-reducing effects of quitting on cardiovascular disease and CVD-related mortality. Extra care should be given to controlling FSG levels among quitters in order to reduce the risk of cardiovascular disease and CVD-related death.