Risk of Cardiovascular Disease from Cumulative Cigarette Use and the Impact of Smoking Intensity

Abstract

Background: Relative risks (RRs) for cardiovascular disease (CVD) by smoking rate exhibit a concave pattern, with RRs in low rate smokers exceeding a linear extrapolation from higher rate smokers. However, cigarettes/day does not by itself fully characterize smoking-related risks. A reexamination of the concave pattern using a comprehensive representation of smoking may enhance insights.

Methods: Data were from the Atherosclerosis Risk in Communities (ARIC) Study, a prospective cohort enrolled in four areas of the US in 1987-1989. Follow-up was through 2008. Analyses included 14,233 participants, 245,915 person-years, and 3,411 CVD events.

Results: The concave RRs with cigarettes/day were consistent with cigarettes/day modifying a linear RR association of pack-years with CVD (i.e., strength of the pack-years association depended on cigarettes/day, indicating that the manner of pack-years accrual impacted risk). Smoking fewer cigarettes/day for longer duration was more deleterious than smoking more cigarettes/day for shorter duration (P < 0.01). For 50 pack-years (365,000 cigarettes), estimated RRs of CVD were 2.1 for accrual at 20 cigarettes/day and 1.6 for accrual at 50 cigarettes/day. Years since smoking cessation did not alter the diminishing strength of association with increasing cigarettes/day. Analyses that accounted for competing risks did not affect findings.

Conclusion: Pack-years remained the primary determinant of smoking-related CVD risk; however, accrual influenced RRs. For equal pack-years, smoking fewer cigarettes/day for longer duration was more deleterious than smoking more cigarettes/day for shorter duration. This observation provides clues to better understanding the biological mechanisms, and reinforces the importance of cessation rather than smoking less to reduce CVD risk.

Figure 1

Relative risks of cardiovascular disease for categories of pack-years of cigarette smoking (solid symbol) relative to never-smokers for all data and within categories of cigarettes/day (CPD) and fitted models, including: linear (solid line), linear-exponential (dash line) and linear adjusted for ever-smoked cigarettes (dot line). All results adjusted for age, birth year, sex and other factors (see text).

Figure 2

Estimated excess relative risk/pack-year (ERR/PKY) for cardiovascular disease within categories of cigarettes/day (solid symbol), with the lowest category further divided into 1–4 and 5–9 cigarettes/day (open symbol), and fitted models for continuous pack-years and cigarettes/day. All results adjusted for age, birth year, sex and other factors (see text).

Figure 3

For coronary heart disease (left panels) and stroke (right panels), relative risks for categories of pack-years of cigarette smoking (solid symbol) relative to never-smokers with fitted linear (solid line) and linear-exponential (dash line) model (upper panels) and estimated excess relative risk/pack-year within categories of cigarettes/day (solid symbol) and fitted models for continuous pack-years and cigarettes/day (solid line) (lower panels). All results adjusted for age, birth year, sex and other factors (see text).

Figure 4

For years since cessation of smoking, relative risks for cardiovascular disease by categories of pack-years of cigarette smoking (solid symbol) relative to never-smokers with fitted linear (solid line) and linear-exponential (dash line) models (left panels) and estimated excess relative risk/pack-year within categories of cigarettes/day (solid symbol) and fitted models for continuous pack-years and cigarettes/day (solid line) (right panels). All results adjusted for age, birth year, sex and other factors (see text).