Long-term management may be necessary in heavy ex-smokers due to cumulative smoking's role in determine post-cessation cardiovascular risk reduction.

"Smoking and CVD risk had a dose-dependent association, and light ex-smokers had a CVD risk similar with that of never-smokers relatively soon after smoking cessation," according to the investigators of a new study.

The CVD risk reduction timeline was examined following smoking cessation, with findings dependent on cumulative smoking exposure measured in pack years. 

In the retrospective study, published in JAMA Network Open, investigators analyzed data for over 5.39 million participants in the Korean National Health Insurance Service. The study included adults classified as current, former, or never-smokers based on biennial self-reported smoking data from 2006 through 2019. The participants with unclear or incomplete smoking histories were excluded, resulting in 5.4 million eligible individuals. Among them, 60.1% were female, 15.8% were current smokers, 1.9% were ex-smokers, and 82.2% were never-smokers. Current and ex-smokers were predominantly male (97% and 98.6%, respectively), whereas only 27.5% of never-smokers were male. Hypertension, diabetes, and dyslipidemia were more prevalent in current and ex-smokers than in never-smokers. 

The participants were stratified by cumulative pack-years (PY), with median exposures of 14 PY for current smokers and 10.5 PY for ex-smokers. Ex-smokers’ median years since quitting (YSQ) were 4 years, with lifetime PY exposure divided into four levels: less than 10, 10 to 20, 20 to 30, and 30 or more PY.

Heavy ex-smokers remained at elevated cardiovascular disease (CVD) risk compared with never-smokers for up to 25 years post-cessation. CVD incidence, recorded as a composite of myocardial infarction, stroke, heart failure, and cardiovascular mortality, totaled 278,315 events.

The incidence rates were 6.03 per 1,000 PY among current smokers, 4.68 for ex-smokers, and 3.37 for never-smokers. In a dose-response trend, higher PY exposure was associated with elevated CVD risk in both current and ex-smokers. 

Further stratification showed CVD risk increased with higher PY among both ex- and current smokers. Among current smokers, CVD risk rose up to 10 PY before plateauing from 10 to 20 PY, with a further increase beyond 20 PY. Among ex-smokers, those with more than 8 PY showed persistent CVD risk, comparable to current smokers.

TCVD risk decreased with time since quitting, with rapid reductions for light ex-smokers (less than 8 PY), who reached risk levels similar to never-smokers within a decade. However, heavy ex-smokers (8 or more PY) continued to face elevated risk, remaining equivalent to current smokers for up to 20 years and only aligning with never-smokers after 25 years. Among those with less than 8 PY, substantial risk reduction was observed within the first 5 YSQ.

The findings underscore cumulative smoking burden's role in determining the timeline for post-cessation CVD risk reduction, suggesting that long-term management may be necessary in heavy ex-smokers.

Conflict of interest disclosures can be found in the original study.