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6th September 2021
Smoking is a risk factor for cardiovascular disease (CVD) and responsible for 1 of every 4 CVD deaths although smoking is a very preventable CVD risk factor. In one observational study of over 8,000 former heavy (i.e., more than 20 cigarettes/day) it was found that within 5 years of cessation, there was a 39% reduced risk of CVD among those who quit, compared to current smokers. Other evidence indicates a potential dose-response relationship between smoking and ischaemic stroke, such that any reduction is beneficial. However, while a meta-analysis has found that reduced use of cigarettes decreases the risk of lung cancer, the impact on CVD was less clear. This led a team from the Department of Family Medicine/Supportive Care Centre, Seoul, Korea, to compare the effect of either smoking cessation or reduction on the risk of cardiovascular disease outcomes. The team used a Korean national health database and collected information of individuals over 40 years of age who had undergone two health examinations in 2009 and again in 2011 to determine any changes in smoking behaviour. A smaller subgroup who had undergone a third examination in 2013 were also included. The team focused on a group of current smokers and excluded those with prior CVD or cancer and used information on smoking status obtained from a biennial national health examination self-administered questionnaire. Individuals were classed as heavy smokers (> 20 cigarettes/day), moderate smokers (10 – 19/day) and light smokers (< 10/day). Compared with the first examination in 2009, participants were then categorised as quitters, reducers I (> 50% reduction), reducers II (20 – 50% reduction), sustainers (reduced by < 20%) and increasers (>20% in smoking). The primary endpoints for the study were newly diagnosed stroke and myocardial infarction (MI) and secondary endpoints included overall mortality, fatal strokes and fatal Mis. Many other health parameters were collected included age, sex, body mass index, duration of smoking, alcohol consumption, levels of exercise, co-morbidities, all of which were adjusted for in the analyses.
A total of 897,975 current smokers with a mean age of 53 years (94.5% male) were followed over 6.2 years. There were a total of 17,748 strokes and 11,271 MI events during the follow-up period. Among smokers, 52.8% were classed as heavy, 37.3% as moderate and the remainder as light during their first examination. Among smoking quitters, there was a significantly reduced risk of stroke (adjusted Hazard ratio, aHR = 0.77, 95% CI 0.74 – 0.81) and MI (aHR = 0.74) compared to sustainers. In addition, smoking cessation was also associated with a significant reduction in all-cause mortality (aHR = 0.92, 95% CI 0.89 – 0.94). However, among reducers I and II, the risk of both stroke and MI were not significantly lower. For example, for reducers I, stroke aHR = 1.02 (95% CI 0.97 – 1.08) and MI aHR = 0.99 (95% CI 0.92 – 1.06).
At the third examination in 2013, quitters who had relapsed to either the level of reducer I, II, sustainer or increaser, had a 42 to 66% increased risk of stroke and a 54 – 69% increased risk of MI compared to quitters, depending where they were in terms of their relapsed level of smoking.
The authors concluded that only smoking cessation and not reduction was associated with a reduced risk of adverse cardiovascular outcomes.
Jeong SM et al. Smoking cessation, but not reduction, reduces cardiovascular disease incidence. Eur Heart J 2021