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.
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