Even a Year of Smoking Can Raise Heart Disease Risk, Study Suggests

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

It is the duty of every healthcare professional to encourage patients to quit smoking. Publicly available initiatives from the World Health Organization aimed at reducing tobacco and tobacco product use provide important information about the harms of smoking and the benefits of quitting (1). It has been observed that heart rate and blood pressure begin to decrease within just 20 minutes of quitting smoking. Information of this kind is increasingly tailored and accessible to both healthcare professionals and patients.

The benefits of quitting smoking continue to increase over time. Coughing and shortness of breath noticeably decrease within just one month. Compared to individuals who continue to smoke long-term, the risk of lung cancer is about 50% lower in those who have quit for 10 years. There is also a reduced risk of developing cancers of the esophagus, throat, and bladder.

Life expectancy is higher in people who quit smoking than in those who continue to smoke. It is estimated that quitting smoking for 30 years can extend life expectancy by up to 10 years. Even at age 60, individuals who quit smoking are expected to live about 3 years longer than smokers. The reduced risk of cardiovascular diseases associated with smoking cessation contributes to increased longevity, although some estimates suggest that this effect may be slightly overstated.

Review and Perspectives of Clinical Study

Various clinical studies have shown that, over time, the cardiovascular disease risk of former smokers may approach that of individuals who have never smoked. However, the time required for this risk to normalize varies widely, ranging from 2 to 20 years. According to more recent data, cardiovascular risk remains elevated for a prolonged period in former heavy smokers—only after approximately 15 years of cessation does it approach the level observed in the general population.

There is a common belief that individuals who have not smoked for 5 years are as healthy as those who have never smoked. However, a clinical study published on August 20, 2019, in The Journal of the American Medical Association indicates that a history of heavy smoking remains a long-term risk factor for cardiovascular disease. Even after quitting, such individuals are often advised to adopt additional lifestyle changes.

Researchers also note that many commonly used cardiovascular risk calculators classify individuals simply as smokers or non-smokers, without accounting for former smokers. Even in tools that include this category (such as the Atherosclerotic CVD Risk Estimator Plus, developed by the American College of Cardiology based on 2013 American Heart Association guidelines), individuals who have not smoked for 5 or more years are often categorized similarly to those who have never smoked.

The number of former smokers continues to grow. To better assess their health and associated risks, it is important to understand how cardiovascular risk factors change over time after smoking cessation.

Framingham Heart Study Data

Data for this clinical study were obtained from the Framingham Heart Study database, including both the original cohort and their offspring. The study included 8,770 participants (average age 42.2 years; 56% were women).

Participants’ smoking habits were assessed repeatedly. The primary cohort was analyzed between 1954 and 1958, while the offspring cohort was analyzed between 1971 and 1975. In both groups, 46.9% of participants were active smokers, 13.6% were former smokers, and 39.5% had never smoked.

Among active smokers, the average number of cigarettes smoked per day was 20. In the former smoker group, the average time since quitting was 5.9 years. Pack-years were also calculated (the number of packs smoked per day multiplied by the number of years of smoking). The average values were 18.8 pack-years in active smokers and 12 pack-years in former smokers.

The relationship between time since smoking cessation and cardiovascular disease risk was analyzed by comparing active smokers, former smokers, and never smokers. One of the study’s major strengths is its long follow-up period of more than 50 years, allowing for more detailed and precise analysis compared to earlier research.

Other cardiovascular risk factors—including age, sex, systolic blood pressure, use of antihypertensive medication, diabetes, cholesterol levels, body mass index, alcohol consumption, and education level—were also evaluated. Previous cardiovascular events such as myocardial infarction, stroke, heart failure, and cardiovascular-related deaths were recorded. However, dietary habits and physical activity were not included, as this information was not consistently collected.

After more than 26 years of follow-up, 2,435 primary cardiovascular events were recorded. Active smoking was associated with a significantly higher number of cardiovascular events per 1,000 people per year compared to never smokers.

Smoking cessation was associated with a reduction in cardiovascular risk, which became apparent relatively quickly. After 5 years of abstinence, the risk was significantly lower (relative risk (RR) 0.61; 95% confidence interval (CI) 0.49–0.76). The difference in event rates between current smokers and those who had quit 5 years earlier was 4.51 per 1,000 people per year (95% CI −5.90 to −2.77).

Unmeasurable Benefit

These findings further support the benefits of quitting smoking. Among individuals with a long history of heavy smoking, cardiovascular disease risk decreased by approximately 39% within 5 years of quitting compared to those who continued smoking.

Former smokers across all groups—including younger individuals, older adults, and those with multiple risk factors—experienced measurable benefits. However, it typically took 10–15 years for cardiovascular risk to approach that of the general population (RR 1.25; 95% CI 0.98–1.60). The difference in event rates between never smokers and those who had quit 10–15 years earlier was 1.27 (95% CI −0.10 to 3.95).

The time required for risk normalization varied between cohorts. In the original cohort, smoking was no longer associated with increased cardiovascular risk 5–10 years after cessation. In the offspring cohort, however, it took at least 25 years for the risk to reach the level observed in never smokers.

Researchers emphasize that 10–15 years represents the minimum time needed for significant risk reduction. In clinical practice, individuals with a history of heavy smoking should be considered at higher cardiovascular risk for decades after quitting. Further large-scale studies are needed to better define the relationship between smoking cessation duration and cardiovascular risk reduction.

The slower risk reduction observed in the offspring cohort may be related to age differences. The average age in the primary cohort was 50 years, compared to 36 years in the offspring cohort. Age becomes an increasingly important cardiovascular risk factor over time, particularly in relation to blood pressure.

Another possible explanation involves generational differences in cigarette composition, which may have become more harmful and more addictive over time.

Researchers also acknowledge that including dietary and physical activity data would have improved the analysis. The American Heart Association recommends a healthy diet and an active lifestyle for former smokers to improve both cardiovascular and respiratory health. Currently, these factors are not included in most cardiovascular risk calculators.

The study focused primarily on long-term heavy smokers to ensure statistical reliability. However, the findings may not fully represent global populations, and therefore should not be used alone to modify international guidelines or risk calculators.

Future research will incorporate smoking history more precisely into cardiovascular risk models, including those based on the Framingham data.

Summary

An editor of The Journal of the American Medical Association noted that these findings are among the most accurate to date. The results are highly relevant for both clinicians and patients.

The study highlights important global trends. In countries such as the United States and Japan, the number of long-term non-smokers is expected to increase, leading to a reduction in cardiovascular disease risk. In contrast, in countries such as China and Indonesia, where smoking rates remain high, the burden of cardiovascular disease is likely to increase.

To reduce smoking prevalence, governments should strengthen regulations on tobacco marketing and sales.

The findings are consistent with a similar study published in the Journal of the American College of Cardiology. The key difference is that the current study suggests the cardiovascular impact of smoking may persist for up to 25 years after cessation, compared to approximately 20 years in earlier research.

Differences between studies may be explained by methodology. One study included peripheral arterial disease, while the other focused on coronary heart disease, stroke, and heart failure. Despite limitations in population diversity, the data and analysis are considered robust.

Both studies emphasize that cardiovascular risk assessment tools should include more detailed information about smoking history.

Clinical Study Highlights

• Data were collected from the original and offspring cohorts of the Framingham Heart Study.
• Smoking status and health data were updated every 2–4 years until 2015.
• The primary outcome was the relationship between smoking cessation and cardiovascular risk.
• Former heavy smokers were compared with former light smokers.
• The study included 8,770 participants (average age 42.2 years; 56% women).
• Approximately 60% of participants were current or former smokers.
• About 38.6% of smokers quit during the study; most did not relapse.
• After 26 years, 2,435 cardiovascular events were recorded.
• Cardiovascular risk decreased significantly within 5 years of quitting.
• Risk normalization took longer in individuals with a history of heavy smoking.

Clinical Significance

• Symptoms such as cough and shortness of breath may improve within one month of quitting.
• After 10 years, lung cancer risk is reduced by approximately 50%.
• Risk of esophageal, throat, and bladder cancers also decreases.
• Long-term smoking cessation can increase life expectancy by up to 10 years.
• Even at age 60, quitting smoking can extend life expectancy by about 3 years.
• Cardiovascular risk decreases by nearly 40% within the first 5 years after quitting.
• However, in heavy smokers, it may take 10–15 years (or longer) for risk to approach that of never smokers.
• Clinicians should consider full smoking history—not just current status—when assessing risk and recommending lifestyle changes.

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