Abstract
BACKGROUND: Uncertainties persist regarding the precise shape of the smoking-outcome curves across various cardiovascular and mortality endpoints. This study aims to elucidate the relationships among smoking burden, intensity, and cessation duration across multiple cardiovascular outcomes.
METHODS AND FINDINGS: Cox proportional hazard models were constructed to evaluate the association between pack-years, cigarettes per day (CPD), and years since cessation with cardiovascular outcomes in participants from 22 prospective cohort studies within the Cross-Cohort Collaboration Tobacco Working Group. We evaluated 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 (AFib), CHD mortality, CVD mortality, and all-cause mortality. Median follow-up varied across outcomes, with 14.4 years for MI (17,570 events), 19.3 years for CHD (30,625 events), 18.6 years for CVD (54,078 events), and approximately 19.4-19.9 years for mortality outcomes (CHD mortality: 17,429 events; CVD mortality: 33,120 events; all-cause mortality: 125,044 events). Spline terms were used to investigate the nonlinear association of continuous smoking/cessation measures with the examined outcomes. Models were adjusted for demographic, socioeconomic, and other cardiovascular risk factors. The study included 323,826 adults (148,635 non-mortality and 176,396 mortality outcomes with 25 and 16 million person-years at risk, respectively). Compared to never-smokers, current smokers had significantly increased risks for CVD (hazard ratio (HR) 1.74, 95% confidence intervals (CIs) [1.66,1.83] in men; HR 2.07, 95% CI [2.00,2.14] in women) and all-cause mortality (HR 2.17, 95% CI [2.09,2.25] in men; HR 2.43, 95% CI [2.38,2.48] in women; all p < 0.001). Compared with never-smokers, participants with 2-5 CPD demonstrated substantially elevated cardiovascular risks, with HR ranging from 1.26 (95% CI [1.09,1.45], p = 0.002) for AFib to 1.57 (95% CI [1.39,1.78], p < 0.001) for HF. Smoking 2-5 CPD was associated with increased CVD mortality (HR 1.57, 95% CI [1.41,1.75]), and all-cause mortality (HR 1.60, 95% CI [1.52,1.69]; both p < 0.001). Smoking 11-15 CPD conferred a higher risk of CVD (HR 1.87, 95% CI [1.69,2.06]) and all-cause mortality (HR 2.30, 95% CI [2.14,2.47]; both p < 0.001). The increased risk associated with the evaluated outcomes was steeper for the initial 20 pack-years and 20 CPD, respectively, compared to further smoking exposure. The most substantial reduction in risk across all outcomes was observed within the first 10 years after smoking cessation. However, the progressive risk reduction continues over extended time periods, with former smokers demonstrating over 80% lower relative risk than those of current smokers within 20 years of cessation. Limitations include potential exposure misclassification due to reliance on single baseline self-reported smoking measurements with extended follow-up periods, which may underestimate true risk associations, and lack of data on other tobacco products and electronic nicotine delivery systems, preventing analysis of dual- and poly-use patterns.
CONCLUSION: Lower-intensity smoking is associated with cardiovascular risk and the primary public health message for current smokers should be early cessation, rather than reducing the amount of smoking. Cessation provides substantial immediate risk reduction, although risk continues to decrease significantly for the following two decades.