No safe level of smoking, study says

Smoking even in low intensity still results in increased cardiovascular risk, reveals a study, noting that the primary public health message for current smokers should be early cessation instead of smoking reduction.

“Cessation provides substantial immediate risk reduction, although risk continues to decrease significantly for the following two decades,” the researchers said.

The associations of pack-years, cigarettes per day (CPD), and years since cessation with cardiovascular outcomes were explored using Cox proportional hazard models in participants from 22 prospective cohort studies within the Cross-Cohort Collaboration Tobacco Working Group.

Myocardial infarction (MI), stroke, coronary heart disease (CHD; MI, coronary revascularization, or coronary death), cardiovascular disease (CVD; stroke or cardiovascular death), heart failure (HF), atrial fibrillation (AF), CHD mortality, CVD mortality, and all-cause mortality were evaluated.

Median follow-up differed across outcomes: 14.4 years for MI (17,570 event), 19.3 years for CHD (30,625 events), 18.6 years for CVD (54,078 events), and 19.4‒19.9 years for mortality outcomes (CHD mortality: 17,429 events; CVD mortality: 33,120 events; all-cause mortality: 125,044 events).

Finally, the researchers examined the nonlinear association of continuous smoking/cessation measures with the examined outcomes using spline terms. Models were adjusted for demographic, socioeconomic, and other cardiovascular risk factors.

A total of 323,826 adults (148,635 nonmortality and 176,396 mortality outcomes with 25 and 16 million person-years at risk, respectively) were included in the analysis. [PLoS Med 2025;22:e1004561]

Current smokers showed significantly higher risks for CVD (men: hazard ratio [HR], 1.74, 95 percent confidence interval [CI], 1.66‒1.83; women: HR, 2.07, 95 percent CI, 2.00‒2.14) and all-cause mortality (men: HR, 2.17, 95 percent CI, 2.09‒2.25; women: HR, 2.43, 95 percent CI, 2.38‒2.48; p<0.001 for all) than never-smokers.

Participants who smoked 2‒5 CPD also showed significantly increased cardiovascular risks compared with never-smokers, with HR range of 1.26 (95 percent CI, 1.09‒1.45; p=0.002) for AF to 1.57 (95 percent CI, 1.39‒1.78; p<0.001) for HF.

Moreover, smoking 2‒5 CPD correlated with increased CVD mortality (HR, 1.57, 95 percent CI, 1.41‒1.75) and all-cause mortality (HR, 1.60, 95 percent CI, 1.52‒1.69; p<0.001 for both), while smoking 11‒15 CPD further increased the risk of CVD by 87 percent (HR, 1.87, 95 percent CI, 1.69‒2.06) and all-cause mortality by 130 percent (HR, 2.30, 95 percent CI, 2.14‒2.47; p<0.001 for both).

Quitting

“The findings of our research underscore the assertion that no level of smoking is without risk,” the researchers said. “Our findings indicate that current smokers using up to 1 CPD [have] elevated risks of cardiovascular and mortality incidents, except for stroke and AF.”

In contrast, the greatest risk reduction across all outcomes was seen within the first 10 years after quitting, according to the researchers.

“However, the progressive risk reduction continues over extended time periods, with former smokers demonstrating over 80 percent lower relative risk than those of current smokers within 20 years of cessation,” they added.