If you think “just a few cigarettes” is a harmless compromise, new research says your heart is not fooled. In an analysis of more than 300,000 adults followed for up to 20 years, people who smoked as little as 2 to 5 cigarettes per day had roughly 50 percent higher risk of cardiovascular disease and 60 percent higher risk of death than people who never smoked, and that elevated risk lingered for decades after quitting.
The findings come from an observational analysis of 22 long running cohort studies in the Cross Cohort Collaboration Tobacco Working Group, led by Erfan Tasdighi and colleagues at the Johns Hopkins Ciccarone Center for Prevention of Cardiovascular Disease and published November 18, 2025 in PLOS Medicine. By pooling detailed data on smoking intensity, cumulative pack years, and years since quitting, the team quantified how cigarette use relates to nine major cardiovascular outcomes and mortality, and concluded that low intensity smoking is far from safe while early, complete cessation delivers the largest reductions in risk.
Across the 323,826 adults included, three quarters were women and almost half were former smokers at baseline. Over nearly two decades of follow up, the collaboration documented more than 125,000 deaths and 54,000 cardiovascular events, including heart attacks, strokes, heart failure, atrial fibrillation, and coronary heart disease. After adjusting for age, sex, race, education, blood pressure, diabetes, cholesterol, medications, and alcohol use, current smokers had about 1.7 to 2.4 times the risk of cardiovascular events and death compared with people who had never smoked, in both men and women.
The shock comes when the authors zoom in on people who smoke relatively little. Among current smokers, those who reported just 2 to 5 cigarettes per day had substantially elevated risks for every outcome they examined. Compared with never smokers, this low intensity group had a 50 percent higher risk of cardiovascular disease, a similar 50 percent higher risk of heart failure, and a 60 percent higher risk of all cause mortality. Even people smoking 1 cigarette per day or less showed increased risk for most cardiovascular endpoints.
No Safe Number Of Cigarettes
Using cubic spline models, the team mapped how risk rises with each additional pack year or cigarette per day. The curves tell a clear story. Risk climbs steeply over the first 20 pack years of smoking and over the first 20 cigarettes per day, then continues to rise but more slowly. In other words, the body absorbs a disproportionate share of harm at relatively modest levels of lifetime smoking, instead of damage increasing in a simple straight line with heavier use.
They also compared people with similar cumulative exposure who either quit or kept smoking. For every pack year category, current smokers carried higher risks than former smokers. Strikingly, former smokers in the heaviest group (more than 20 pack years) had lower cardiovascular and mortality risks than current smokers in the lightest group (5 pack years or less), underscoring that quitting matters more than total past consumption when it comes to future outcomes.
As the authors put it:
“This is one of the largest studies of cigarette smoking to date using the highest quality data in the cardiovascular epidemiology literature. It is remarkable how harmful smoking is, even low doses of smoking confer large cardiovascular risks. As far as behavior change, it is imperative to quit smoking as early in life as possible, as the among of time passed since complete cessation from cigarettes is more important prolonged exposure to a lower quantity of cigarettes each day.”
That pattern held across a wide range of cardiovascular diagnoses. Hazard ratios for current smokers remained elevated for myocardial infarction, stroke, coronary heart disease, heart failure, atrial fibrillation, cardiovascular mortality, and all cause mortality. Former smokers sat in the middle, with risks consistently higher than never smokers but substantially lower than those who continued to smoke.
Quitting Early Beats Cutting Back
If low intensity smoking is not safe, the next question is how quickly risk falls after quitting. Here too, the data are surprisingly hopeful. Among former smokers, the largest drop in risk across all outcomes occurred in the first 10 years after cessation, with risk continuing to decline over the following decade. Within 20 years of quitting, former smokers had more than 80 percent lower relative risk than current smokers, although their risk often remained modestly higher than that of never smokers, even after 21 to 30 years.
By modeling cessation duration and pack years together, the team showed that time since quitting carries more weight than additional increments of past exposure. In their heat maps, risk bands shift more dramatically along the years since cessation axis than along the pack year axis. Roughly speaking, gaining an extra 5 to 10 years as a former smoker can offset the risk associated with 30 to 50 additional pack years of prior smoking history. People who quit young and stay smoke free for decades approach, but do not fully reach, the cardiovascular risk profile of people who never smoked at all.
The core message is blunt and aimed squarely at current smokers and their clinicians:
“The primary public health message of our paper is the importance of complete smoking cessation at younger ages.”
Cutting back from a pack a day to a few cigarettes a day does reduce risk, but this new analysis shows that even those few cigarettes still carry substantial danger, and that simply reducing intensity is a poor substitute for stopping altogether. Recent cohorts enrolled after 2001 actually showed stronger smoking related risks than earlier cohorts, suggesting that relative harms have grown as background cardiovascular care improves for never smokers.
For public health, the implications are straightforward. There is no safe level of cigarette smoking for the heart, and prevention efforts should treat “social” or “light” smoking as serious exposure, not a tolerable compromise. For people who already smoke, every year earlier they quit appears to buy back meaningful cardiovascular health, with the steepest benefits in the first decade after cessation and continued gains over at least two more.
The open access paper is available in PLOS Medicine at https://plos.io/4nIQAXN.
PLOS Medicine: 10.1371/journal.pmed.1004561
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