It takes somewhere between 10 and 15 years—and possibly up to 25—after quitting tobacco for former heavy smokers’ CVD risk to revert to pre-smoking levels, according to a study published August 20 in the Journal of the American Medical Association.
Meredith S. Duncan, MA, of Vanderbilt University, and colleagues’ research sought to better quantify how long it takes for the excess CV risk associated with smoking to regress to the levels of a never-smoker—a period that’s been estimated to last anywhere from 2 to 20 years. The Atherosclerotic CVD Risk Estimator Plus, a tool endorsed by the American College of Cardiology and American Heart Association, considers former smokers’ CVD risk identical to never-smokers’ after just five years.
“Uncertainty about the time course of CVD risk reduction following smoking cessation could underestimate CVD risk among former smokers, a group increasing as U.S. smoking prevalence declines,” Duncan and her team wrote in JAMA.
The researchers retrospectively analyzed data from the Framingham Heart Study, focusing on a subgroup of 8,770 individuals without baseline CVD. The study population was defined by two distinct cohorts: the original cohort, which comprised 3,805 patients who had attended their fourth exam between 1954 and 1958, and an offspring cohort of 4,965 patients who’d attended their first exam between 1971 and 1975. Participants were followed through December 2015.
Of the full study population, 5,308 individuals were ever-smokers with an average of 17.2 baseline pack-years between them. Smokers included 2,371 self-reported heavy ever-smokers, 17% former and 83% current.
Over a median of 26.4 years of follow-up, Duncan et al. noted 2,435 first CVD events, 1,612 of which occurred in the original cohort and 823 of which took place in the offspring cohort (with more than half of cases attributed to heavy smokers). In the pooled cohort, compared with being a current smoker, quitting within five years was linked to:
- Lower rates of incident CVD (6.94 cases per 1,000 person-years compared to 11.56 cases per 1,000 person-years)
- Lower risk of incident CVD (39% reduced risk)
Compared with never smoking, quitting tobacco wasn’t linked to a greater risk of CVD between 10 and 15 years after cessation (incidence rates of 5.09 per 1,000 person-years vs. 6.31 per 1,000 person-years in people who never smoked vs. people who quit within 10 to 15 years, respectively). That means a former smoker’s risk of CVD doesn’t approximate the risk of a never-smoker until 10 to 15 years after kicking the habit.
“Smoking cessation improves cardiovascular health, but not right away,” Thomas B. Cole, MD, MPH, associate editor of JAMA, said in an editor’s note. “The risk of CVD does appear to decline substantially within the first five years, and smokers who are contemplating quitting may take some encouragement from this finding.”
Still, Cole wrote, on a population level, the implications of Duncan et al.’s findings are “sobering.”
“Reductions in CVD associated with declining smoking rates in countries such as Japan and the United States can be expected to lag quit rates by 10 to 15 years, and in countries where smoking rates appear to be increasing, such as China and Indonesia, rates of CVD are likely to increase for decades into the future,” he wrote.