Heavy cigarette smokers with at least a 20 pack-year smoking history can reduce their risk of cardiovascular disease (CVD) by 39% within five years if they quit, according to a US study. But it takes at least five to 10 years, and perhaps up to 25 years after quitting, for CVD risk to become as low as that of a similar person who has never smoked.
"Previous studies have shown the association between quitting and reduced CVD risk," said lead author, Dr Meredith Duncan, who led the analyses for the division of cardiovascular medicine at Vanderbilt University Medical Centre. "But the current Atherosclerotic CVD Risk Calculator, which is routinely used in clinical practice, considers former smokers' risk to be similar to that of never smokers after five years of cessation, which is not consistent with these findings."
Cigarette smoking is responsible for 20% of CVD deaths in the US, the study notes.
Researchers used data from the Framingham Heart Study, a longitudinal study of men and women from Framingham, Massachusetts, which began enrolment in 1948 and now includes their children and grandchildren, as well as multi-ethnic cohorts.
The study used prospective data from 1954 through 2014 from 8,770 participants – 3,805 from the Original cohort and 4,965 from the Offspring cohort – to determine the effect of lifetime smoking and smoking cessation on the risk of CVD, which includes myocardial infarction, stroke, CVD death and heart failure.
"The Framingham Heart Study provides particularly robust data on lifetime smoking history," added Duncan. "Our team leveraged this unique opportunity to document what happens to CVD risk after quitting smoking relative to people who continued to smoke and to those who never smoked."
Senior author Dr Hilary Tindle, medical director of the VUMC Tobacco Treatment Service and founding director of the Vanderbilt Centre for Tobacco Addiction and Lifestyle (ViTAL), urges smokers to act on these study results by putting out their cigarettes.
"The cardiovascular system begins to heal relatively quickly after quitting smoking, even for people who have smoked heavily over decades," Tindle said. "Full recovery could take years, so now is a great time to quit smoking and take other steps toward heart health."
Importance: The time course of cardiovascular disease (CVD) risk after smoking cessation is unclear. Risk calculators consider former smokers to be at risk for only 5 years.
Objective: To evaluate the association between years since quitting smoking and incident CVD.
Design, Setting, and Participants: Retrospective analysis of prospectively collected data from Framingham Heart Study participants without baseline CVD (original cohort: attending their fourth examination in 1954-1958; offspring cohort: attending their first examination in 1971-1975) who were followed up through December 2015.
Exposures: Time-updated self-reported smoking status, years since quitting, and cumulative pack-years.
Main Outcomes and Measures: Incident CVD (myocardial infarction, stroke, heart failure, or cardiovascular death). Primary analyses included both cohorts (pooled) and were restricted to heavy ever smokers (≥20 pack-years).
Results: The study population included 8770 individuals (original cohort: n = 3805; offspring cohort: n = 4965) with a mean age of 42.2 (SD, 11.8) years and 45% male. There were 5308 ever smokers with a median 17.2 (interquartile range, 7-30) baseline pack-years, including 2371 heavy ever smokers (406 [17%] former and 1965 [83%] current). Over 26.4 median follow-up years, 2435 first CVD events occurred (original cohort: n = 1612 [n = 665 among heavy smokers]; offspring cohort: n = 823 [n = 430 among heavy smokers]). In the pooled cohort, compared with current smoking, quitting within 5 years was associated with significantly lower rates of incident CVD (incidence rates per 1000 person-years: current smoking, 11.56 [95% CI, 10.30-12.98]; quitting within 5 years, 6.94 [95% CI, 5.61-8.59]; difference, −4.51 [95% CI, −5.90 to −2.77]) and lower risk of incident CVD (hazard ratio, 0.61; 95% CI, 0.49-0.76). Compared with never smoking, quitting smoking ceased to be significantly associated with greater CVD risk between 10 and 15 years after cessation in the pooled cohort (incidence rates per 1000 person-years: never smoking, 5.09 [95% CI, 4.52-5.74]; quitting within 10 to <15 years, 6.31 [95% CI, 4.93-8.09]; difference, 1.27 [95% CI, −0.10 to 3.05]; hazard ratio, 1.25 [95% CI, 0.98-1.60]).
Conclusions and Relevance: Among heavy smokers, smoking cessation was associated with significantly lower risk of CVD within 5 years relative to current smokers. However, relative to never smokers, former smokers’ CVD risk remained significantly elevated beyond 5 years after smoking cessation.
Meredith S Duncan, Matthew S Freiberg, Robert A Greevy, Suman Kundu, Ramachandran S Vasan, Hilary A Tindle