Quitting smoking significantly reduces the risk of cardiovascular disease, but past smokers are still at elevated cardiovascular risk, compared with nonsmokers, for up to 25 years after smoking cessation, research in JAMA suggests.
AtnoYdur/Thinkstock
A retrospective analysis of data from 8,770 individuals in the Framingham Heart Study compared the incidence of myocardial infarction, stroke, heart failure, or cardiovascular death in ever-smokers with that of never smokers.
Only 40% of the total cohort had never smoked. Of the 4,115 current smokers at baseline, 38.6% quit during the course of the study and did not relapse but 51.4% continued to smoke until they developed cardiovascular disease or dropped out of the study.
Current smokers had a significant 4.68-fold higher incidence of cardiovascular disease, compared with those who had never smoked, but those who stopped smoking showed a 39% decline in their risk of cardiovascular disease within 5 years of cessation.
However, individuals who were formerly heavy smokers – defined as at least 20 pack-years of smoking – retained a risk of cardiovascular disease 25% higher than that of never smokers until 10-15 years after quitting smoking. At 16 years, the 95% confidence interval for cardiovascular disease risk among former smokers versus that of never smokers finally and consistently included the null value of 1.
The study pooled two cohorts; the original cohort, who attended their fourth examination during 1954-1958 and an offspring cohort who attended their first examination during 1971-1975. The authors saw a difference between the two cohorts in the time course of cardiovascular disease risk in heavy smokers.
In the original cohort, former heavy smoking ceased to be significantly associated with increased cardiovascular disease risk within 5-10 years of cessation, but in the offspring cohort, it took 25 years after cessation for the incidence to decline to the same level of risk seen in never smokers.
“The upper estimate of this time course is a decade longer than that of the Nurses’ Health Study results for coronary heart disease and cardiovascular death and more than 20 years longer than in some prior reports for coronary heart disease and stroke,” wrote Meredith S. Duncan from the division of cardiovascular medicine at the Vanderbilt University Medical Center, Nashville, Tenn., and coauthors. “Although the exact amount of time after quitting at which former smokers’ CVD risk ceases to differ significantly from that of never smokers is unknown (and may further depend on cumulative exposure), these findings support a longer time course of risk reduction than was previously thought, yielding implications for CVD risk stratification of former smokers.”
However, they did note that the study could not account for environmental tobacco smoke exposure and that the participants were mostly of white European ancestry, which limited the generalizability of the findings to other populations.
The Framingham Health Study was supported by the National Heart, Lung, and Blood Institute. One author declared a consultancy with a pharmaceutical company on a proposed clinical trial. No other conflicts of interest were declared.
SOURCE: Duncan M et al. JAMA 2019. doi: 10.1001/jama.2019.10298.