| Summary: | BACKGROUND: Relative risks (RR) 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. MATERIAL: Data were from the Atherosclerosis Risk in Communities (ARIC) Study, a prospective cohort enrolled in four areas of the U.S. in 1987-89. 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 packyears 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 packyears (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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