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Cardiovascular risk of smoking may last up to 25 years, new study
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"Among heavy smokers, smoking cessation was associated with significantly lower CVD risk within 5 years relative to current smokers. However, relative to never smokers, former smokers' risk remained significantly elevated beyond 5 years after smoking cessation.......This study found that compared with current heavy smoking, smoking cessation among former heavy smokers was associated with lower CVD risk within 5 years of cessation, reaffirming the cardiovascular benefit of smoking cessation demonstrated by others8,10-12,27 but also revealing a slow ensuing CVD risk decline over decades (Figure 2). Compared with never smoking, it took 10 to 15 years (pooled cohort) (5 to 10 years in the original cohort and ≥25 years in the offspring cohort) following cessation for former heavy smoking (vs never smoking) to cease being significantly associated with elevated CVD risk."
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Cardiovascular cost of smoking may last up to 25 years
Publish date: August 20, 2019
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.
https://www.mdedge.com/cardiology/article/206705/cad-atherosclerosis/cardiovascular-cost-smoking-may-last-25-years
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Editor's Note
August 20, 2019
Smoking Cessation and Reduction of Cardiovascular Disease Risk
Thomas B. Cole,MD, MPH
Smoking cessation improves cardiovascular health, but not right away. Studies have come to different conclusions about how long it takes for the excess risk associated with smoking to subside to the level of a never smoker, with estimates varying widely, from 2 to 20 years. The study by Duncan et al,1 which was based on repeated assessments of tobacco exposure, other risk factors, and cardiovascular disease (CVD) outcomes, provides estimates of cardiovascular risk among former smokers that are likely to be more precise and accurate than those of previous studies. This information is important for clinicians and patients. According to these new analyses, a former smoker's risk of CVD does not approximate the risk of a never smoker until 10 to 15 years have elapsed since cessation. The risk of CVD does appear to decline substantially within the first 5 years, and smokers who are contemplating quitting may take some encouragement from this finding. On a population level, the implications of this study are sobering: reductions in CVD associated with declining smoking rates in countries such as Japan and the United States2 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. To counter these trends, all countries, particularly those most vulnerable to tobacco marketing, should implement tobacco control strategies to prevent smoking initiation and motivate current smokers to quit.
Association of Smoking Cessation With Subsequent Risk of Cardiovascular Disease
JAMA. aug 20 2019 - Meredith S. Duncan, MA; Matthew S. Freiberg, MD, MSc; Robert A. Greevy Jr, PhD; Suman Kundu, DSc, MSc; Ramachandran S. Vasan, MD; Hilary A. Tindle,MD, MPH
Key Points
Question Among heavy smokers (ie, ≥20 pack-years), what is the association between time since smoking cessation and subsequent risk of cardiovascular disease?
Findings In this observational cohort study of 8770 participants, former heavy smokers' risk of cardiovascular disease was significantly lower within 5 years of smoking cessation relative to current smokers (hazard ratio, 0.61) but remained significantly elevated for at least 5 to 10 years and possibly for 25 years after cessation relative to never smokers.
Meaning Compared with never smokers, former heavy smokers may have significantly elevated cardiovascular disease risk beyond 5 years after cessation.
Abstract
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.
Introduction
Cigarette smoking is a risk factor for cardiovascular disease (CVD) and is responsible for 20% of CVD deaths in the United States1-6; smoking cessation reduces CVD risk.7 However, estimates of the time course of CVD risk reduction among former smokers following cessation have been inconsistent relative to persistent smokers (2-10 years),8-12 and never smokers (2-20 years).8-12
Some clinical CVD risk calculators do not distinguish risk between never smokers and former smokers.13 The Atherosclerotic CVD (ASCVD) Risk Estimator Plus allows clinicians to identify former smokers but considers their CVD risk identical to never smokers after 5 years.14 Uncertainty about the time course of CVD risk reduction following smoking cessation could underestimate CVD risk among former smokers, a group increasing as US smoking prevalence declines.15
Cardiovascular disease risk estimates among former smokers could be improved by frequent, long-term smoking exposure assessment (including status, intensity, abstinence periods, and relapse), objective and time-updated assessment of other CVD risk factors, and continuous CVD incidence surveillance. Data from the Framingham Heart Study (FHS) were analyzed to determine the association between years since smoking cessation and subsequent CVD risk among former smokers relative to persistent smokers and never smokers.
Discussion
This study found that compared with current heavy smoking, smoking cessation among former heavy smokers was associated with lower CVD risk within 5 years of cessation, reaffirming the cardiovascular benefit of smoking cessation demonstrated by others8,10-12,27 but also revealing a slow ensuing CVD risk decline over decades (Figure 2). Compared with never smoking, it took 10 to 15 years (pooled cohort) (5 to 10 years in the original cohort and ≥25 years in the offspring cohort) following cessation for former heavy smoking (vs never smoking) to cease being significantly associated with elevated CVD risk.
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 death8,28 and more than 20 years longer than in some prior reports for coronary heart disease10,11 and stroke.29 Results from the British Regional Heart Study12 found myocardial infarction risk to persist for more than 20 years after cessation, but findings were limited to men and smoking data were assessed only at baseline. Prior studies primarily examined single CVD components as opposed to composite CVD. In analyses of the full cohort (ie, including those with <20 pack-years), former smoking (vs never smoking) was no longer significantly associated with excess CVD risk within 10 to 15 years of cessation, highlighting the need to stratify by cumulative pack-years. 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.
Currently, the ASCVD Risk Estimator Plus14 is used by clinicians to help inform patients regarding their 10-year and lifetime CVD risk and to guide behavior changes to reduce CVD risk. Despite limitations,30,31 this model is well calibrated in the population for which it was intended32 and, importantly, improves on prior CVD risk calculators13,33-35 by differentiating risk between former and never smokers. However, the tool considers risk in former smokers to be equivalent to that of never smokers after 5 years since quitting. Thus, as the proportion of former smokers in the United States increases with more current smokers quitting, so does the potential to underestimate CVD risk using current tools, especially among heavier smokers. The present investigation does not support the assumption that former smokers achieve the same CVD risk as never smokers within 5 years of quitting. Future studies should investigate the extent to which including comprehensive data on smoking exposure, such as pack-years smoked and years since quitting, would improve the performance of existing CVD risk prediction tools and, by extension, CVD health outcomes.
In Figure 2A, CVD risk appeared to increase at about 10 years after cessation among former heavy smokers, but only when current smokers were included in the analysis. However, 95% confidence bands include a smooth decline in risk without this artifactual increase, as evidenced by the smooth curve when current smokers are not included (Figure 2B).
A strength of the present analysis is the rich data source including 2 distinct but similar cohorts with a median follow-up of more than 26 years. The FHS features frequent, repeated, in-person assessments of smoking status and intensity over the course of half a century or more, allowing for comprehensive lifetime capture of smoking. In addition, the FHS simultaneously collected data on CVD risk factors, which allows robust adjustment for confounders. Continuous participant follow-up for CVD incidence also allows for accurate and near-complete event capture. This investigation extends prior knowledge by using a self-reported smoking ascertainment method, including prospectively gathered and regularly time-updated data on smoking status and intensity collected during in-person visits. Sensitivity analyses with fewer smoking status assessments led to inconsistent results in which relative risk among former smokers did not decrease in a monotonic fashion with increasing years since quitting.
In lifetime analyses, people develop comorbidities with increasing age, which could influence smoking cessation patterns. To minimize this potential bias from unmeasured confounding, analyses accounted for baseline differences between cohorts (eg, age), differences among current, former, and never smokers, temporal trends (eg, declining smoking rate, increasing BMI), birth cohort effects, and factors that could influence both smoking cessation and CVD risk, including sociodemographic factors and known CVD risk factors, which were time-updated. Thus, the effect of unmeasured confounding on the overall findings is likely modest.
Limitations
This study also has several limitations. First, compared with some prior studies,26 the sample size was smaller, but it was large enough to address the questions of interest and also provided thoroughly captured longitudinal smoking data. The limited sample size also precluded analyses yielding CVD risk estimates among subcategories of lighter smokers (<20 lifetime pack-years); thus, the primary findings are applicable to ever smokers with a cumulative smoking history of at least 20 pack-years. Second, information on environmental tobacco smoke exposure and use of other types of tobacco was not available for most participants and was not included. Third, as with other investigations using data from the FHS original and offspring cohorts, this investigation is composed primarily of white individuals of European ancestry, potentially limiting generalizability of results to individuals of other races/ethnicities.
Conclusions
Among heavy smokers, smoking cessation was associated with significantly lower CVD risk within 5 years relative to current smokers. However, relative to never smokers, former smokers' risk remained significantly elevated beyond 5 years after smoking cessation.
Results
There were 8770 participants (3805 original cohort members and 4965 offspring cohort members) meeting inclusion criteria (Figure 1). In the pooled cohort, the mean age was 42.2 years (SD, 11.8 years), 56% were female, and 75% had at least a high school education (Table 1). Only 2% and 27% of the cohort had baseline diabetes and hypertension, respectively, and median BMI (calculated as weight in kilograms divided by height in meters squared) was in the normal range (median, 24.8; interquartile range, 22.4-27.7), but 78% of the cohort consumed alcohol in the past year (current drinkers), and only 40% of the cohort had never smoked. 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). In the original and offspring cohorts, heavy former and current smokers (≥20 pack-years) had similar cumulative pack-year distributions (eFigure in the Supplement) and CVD risk factors (eTables 1 and 2 in the Supplement). The proportion of missing data was low; 89% of offspring cohort person-examinations had complete data. However, in the original cohort, only 51% of person-examinations had complete data because information on alcohol consumption and blood glucose levels was not collected at all examinations.
Of 4115 current smokers at baseline, 1589 (38.6%) quit and never relapsed, while 2117 (51.4%) continued to smoke until they developed CVD or were censored. Most (84.7%) baseline former smokers remained abstinent during follow-up. Among baseline ever smokers, there were 591 smokers who relapsed (ie, began smoking again after reporting abstinence during at least 1 clinic visit). Abstinence periods ranged from 0 to 68 years (median, 3 years; interquartile range, 0-15 years).
During a 26.4-year median follow-up, participants experienced 2435 first CVD events (1612 in the original cohort and 823 in the offspring cohort) (eTable 3 in the Supplement). In both cohorts pooled and separately, current smoking was associated with significantly higher CVD incidence rates per 1000 person-years vs never smoking (Table 2). Incidence rate differences were 4.68 (95% CI, 3.56-5.99) in the pooled cohort, 5.00 (95% CI, 3.17-7.25) in the original cohort, and 4.50 (95% CI, 3.20-6.10) in the offspring cohort. After further categorizing current smokers by pack-years, the association was attenuated in the original cohort with less than 20 cumulative pack-years (incidence rate difference, 0.61; 95% CI, -1.73 to 3.57) but remained significant for current smokers with 20 or more pack-years in the original cohort (incidence rate difference, 6.62; 95% CI, 4.48-9.27) and all current smokers in both the offspring cohort (incidence rate difference among those with <20 pack-years, 3.03 [95% CI, 1.13-5.83] and among those with ≥20 pack-years, 4.92 [95% CI, 3.48-6.68]) and the pooled cohort (incidence rate difference among those with <20 pack-years, 1.65 [95% CI, 0.07-3.62] and among those with ≥20 pack-years, 6.00 [95% CI, 4.61-7.51]) (Table 2). Former heavy smoking in the pooled cohort and offspring cohort was also associated with increased CVD incidence compared with never smoking (pooled cohort incidence rate difference, 1.12 [95% CI, 0.26-2.04]; offspring cohort incidence rate difference, 1.42 [95% CI, 0.68-2.32]) (Table 2).
In adjusted models, smoking cessation was associated with a rapid decline in CVD risk vs continued smoking (Figure 2) such that risk was significantly lower within 5 years of cessation in the pooled cohort (HR, 0.61 [95% CI, 0.49-0.76]; 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]) (Table 3). In sensitivity analyses adjusting for cumulative pack-years, results were similar (HR, 0.62 [95% CI, 0.50-0.77]; incidence rate difference, -4.29 [95% CI, -5.64 to -2.59]) (eTable 4 in the Supplement). However, former heavy smoking was associated with higher CVD risk compared with never smoking until 10 to 15 years after cessation in the pooled cohort (HR, 1.25 [95% CI, 0.98-1.60]; 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]) (Table 3). As shown in Figure 2, 16 years after cessation was the point at which the 95% confidence interval for CVD risk among former smokers vs never smokers consistently included the null value of 1. Results remained consistent whether current smokers (ie, years since quitting = 0) were included in the analysis (HR, 1.16 [95% CI, 0.98-1.37]; incidence rate difference, 0.94 [95% CI, -0.12 to 2.17]) (Figure 2A) or not included in the analysis (HR, 1.17 [95% CI, 0.99-1.39]; incidence rate difference, 1.00 [95% CI, -0.06 to 2.29]) (Figure 2B). The time course of CVD risk appeared to differ by cohort (Table 3). In the original cohort, former heavy smoking was no longer significantly associated with increased CVD risk compared with never smoking within 5 to 10 years of cessation (HR, 1.28 [95% CI, 0.97-1.69]; incidence rate difference, 1.88 [95% CI, -0.20 to 4.64]), while in the offspring cohort, this did not occur until at least 25 years after cessation (HR, 1.10 [95% CI, 0.79-1.54]; incidence rate difference, 0.26 [95% CI, -0.54 to 1.39]). Sensitivity analyses with linear terms for continuous covariates instead of polynomial terms were comparable (eTable 5 in the Supplement).
Incidence rates of CVD among current smokers were higher in the original cohort (13.04; 95% CI, 11.21-15.18) than in the offspring cohort (7.71; 95% CI, 6.27-9.48) (Table 3). These differences were substantially attenuated in sensitivity analyses restricted to offspring person-examinations among heavy ever smokers and never smokers aged 50 years or older (incidence rate among current smokers, 11.50; 95% CI, 8.94-14.78) (eTable 6 in the Supplement). In sensitivity analyses including all ever smokers, results comparing CVD risk in former vs current and never smokers were similar (among former smokers quitting <5 years prior vs current smokers: HR, 0.60 [95% CI, 0.50-0.72]; incidence rate difference, -3.92 [95% CI, -4.91 to -2.75]; among former smokers quitting 10-15 years prior vs never smokers: HR, 1.08 [95% CI, 0.88-1.33]; incidence rate difference, 0.38 [95% CI, -0.57 to 1.56]) (eTable 7 in the Supplement). Compared with primary analyses using all available follow-up time points, sensitivity analyses with 6 smoking status assessments produced estimates of similar magnitude but using fewer smoking status assessments produced risk estimates that did not monotonically decrease with years since quitting (eTables 8 and 9 in the Supplement).
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