How does a year of smoking change the risk of cardiovascular disease?
Gabija Visockytė Vilnius University Faculty of Medicine
Prepared according to Anderson P, Vega CP. What Is the Effect of Smoking Cessation and Cardiovascular Risk? Medscape Education Clinical Briefs, October 11, 2019.
Clinical Relevance
Every healthcare professional has a duty to encourage their patients to quit smoking. Public initiatives from the World Health Organization related to reducing tobacco consumption provide crucial information about the harms of smoking and the benefits of quitting (1). Heart rate and blood pressure start to decrease within just 20 minutes of quitting smoking. Detailed information is tailored and accessible to both healthcare professionals and patients.
The true benefits of quitting smoking increase over time. Coughing and shortness of breath noticeably decrease within just one month of quitting. Compared to someone who has been smoking constantly for a long time, the risk of lung cancer for those who quit smoking for 10 years becomes 50% lower (1). Furthermore, the risk of cancers in the esophagus, throat, and bladder also decreases (1). Lifespan extensions are significant, with those quitting smoking for 30 years gaining an estimated extra 10 years (1). Even at 60 years old, those who quit smoking have a life expectancy that is 3 years longer than that of constant smokers (1). The reduced risk of cardiovascular diseases and events associated with quitting smoking also contributes to longevity, although this effect may sometimes be overestimated (1).
Review and Perspectives of Clinical Studies
Various clinical studies reveal that the long-term risk of cardiovascular diseases for individuals who have never smoked and those who have quit eventually becomes equal (2). However, the interval from quitting smoking to when this risk matches the general population's level can range widely, from 2 to 20 years (2). According to the latest data, the risk of cardiovascular diseases remains elevated for previously heavy smokers, with the risk leveling out only 15 years after quitting (2).
A common societal belief exists that those who haven't smoked for 5 years are as healthy as the general population (2). However, a clinical study published on August 20, 2019, in The Journal of the American Medical Association, highlights that a history of active and heavy smoking remains a long-term cardiovascular risk factor (2). Therefore, such patients often need additional lifestyle changes even if they have quit smoking long ago (2). Most automatic cardiovascular disease risk calculators make a binary distinction between smokers and non-smokers, without considering those who have quit. Even the Atherosclerotic CVD Risk Estimator Plus, developed by the American College of Cardiology under the 2013 American Heart Association guidelines, automatically equates a patient who has quit for over 5 years to a never-smoker (2). The growing ranks of ex-smokers make it crucial to determine how cardiovascular disease risk factors change over time for better health assessments (2).
Framingham Heart Study Data
Data for the latest clinical study came from the Framingham Heart Study database, utilizing the original cohort data and that of their offspring (3). The study included 8,770 participants (average age 42.2 years, 56% were women) (3). Researchers evaluated the participants' smoking habits repeatedly (3). The primary analysis started in 1954-1958, and the analysis of their offspring occurred in 1971-1975 (3). In both groups, 46.9% were active smokers, 13.6% had quit smoking, and 39.5% had never smoked (3). Among active smokers, the average number of cigarettes smoked per day was 20, and ex-smokers had an average time since their last cigarette of 5.9 years (3). Pack-years—cigarette packs per day multiplied by active smoking years—were 18.8 for active smokers and 12 for ex-smokers (3).
Researchers examined the relationship between the time since quitting smoking and cardiovascular disease risk by comparing active smokers, ex-smokers, and never smokers (3). The extensive data collection over more than 50 years provided more detailed and precise insights than previous studies (3). The analysis also considered other risk factors like age, gender, systolic blood pressure, antihypertensive medication use, diabetes, cholesterol levels, body mass index, alcohol consumption habits, and patient education (3). Previous cardiovascular events such as myocardial infarctions, strokes, heart failures, and cardiovascular-related deaths were also included in the evaluation (3).
By the study's halfway point, after more than 26 years since its inception, the study registered 2,435 primary cardiovascular events in the overall study group (3). Active smoking correlated with a significantly higher number of cardiovascular events per 1,000 people per year compared to never smokers and the general population (3). Quitting smoking showed a decrease in cardiovascular disease risk, which became significant almost immediately (3). Just 5 years of not smoking showed a significantly lower relative risk (RR) of 0.61 (95% confidence interval (CI) 0.49-0.76) (3). The difference in event rates per 1,000 people per year between active smokers and those who quit 5 years ago was -4.51 (95% CI -5.90 to -2.77) (3).
Unmeasurable Benefits
The study results strongly support the benefits of quitting smoking. Participants with a long history of heavy smoking saw a 39% decrease in cardiovascular disease risk after 5 years of quitting, compared to those who continued smoking (3). All former smokers noticed positive changes after quitting—regardless of age or concurrent risk factors (3). Nevertheless, it took 10-15 years for quitters' cardiovascular disease risk to reach the general population level (RR 1.25, 95% CI 0.98-1.60) (3). The difference in event rates between never smokers and those who quit 10-15 years ago was 1.27 (95% CI -0.10 to 3.95) (3).
The time required to normalize risk varied between study groups (3). In the primary study group, smoking was no longer linked to increased cardiovascular risk 5-10 years after quitting (3). However, in the offspring group, this risk only matched the general population level after at least 25 years (3). Researchers point to the age difference (average age 50 in the primary group vs. 36 in the offspring group) as a significant factor (3). Additionally, changes in cigarette composition over time may have contributed to the prolonged risk in the offspring group (3).
Monitoring dietary and physical activity habits could have clarified the situation, but the study did not include this data consistently (3). The American Heart Association recommends a healthy and balanced diet, and an active lifestyle for former smokers to strengthen heart and lung function and boost physical endurance (3). Diet and physical activity currently are not part of any cardiovascular risk calculator (3).
For statistical reliability and precise results, the study focused on long-term heavy smokers (3). Based on previous studies on lung cancer, researchers predicted the highest risk in active smokers (3). Although the study did not represent the entire world population, the findings highlight the need for updates to international guidelines and risk calculators based on more comprehensive data (3). The next stage of the clinical study aims to apply methods from the Atherosclerotic Cardiovascular Disease Risk Calculator, incorporating additional patient smoking status information (3).
References
1. Tobacco Free Initiative (TFI). Fact sheet about health benefits of smoking cessation. https://www.who.int/tobacco/quitting/benefits/en/. Accessed August 20, 2019. 2. Duncan MS, et al. Association of smoking cessation with subsequent risk of cardiovascular disease. JAMA. 2019;322(7):642-650. 3. Cole TB. Smoking Cessation and Reduction of Cardiovascular Disease Risk. JAMA. 2019;322(7):651. 4. Ding N, et al. Cigarette smoking, smoking cessation, and long-term risk of 3 major atherosclerotic diseases. J Am Coll Cardiol. 2019;74(4):498-507.
Publication "Internist" No. 8, 2019
