Even low-level exposure to secondhand smoke and air pollution increases cardiovascular risk.
The link between airborne fine particulate matter (PM) and cardiovascular disease — and the thresholds at which risk escalates — remain controversial. To assess the adjusted relative risks for cardiovascular mortality according to various levels of exposure to fine PM — ranging from air pollution and secondhand cigarette smoke (0.18–0.90 mg/day of fine PM) to active cigarette-smoke inhalation (18–324 mg/day of fine PM) — epidemiologists studied prospectively collected data on >1 million adults (mean age, 57) who participated in the American Cancer Society's 1982 Cancer Prevention Study II.
During a follow-up period of about 6 years, CVD mortality risk increased by 64% in participants who smoked three or fewer cigarettes per day and doubled in those who smoked a pack or more per day. Importantly, even at the low exposure levels of ambient air pollution and secondhand cigarette smoke, adjusted relative mortality risks were significantly increased and exceeded those that would be predicted by a linear exposure-response association.
Comment: In this large epidemiologic study, CVD mortality risk increased not only at very low levels of active cigarette smoking but also at exposure levels associated with secondhand cigarette smoke and ambient air pollution. Given that recent estimates of average particulate air pollution concentrations in urban areas of China, India, and other developing countries have exceeded 100 µg/m3 (compared with concentrations of 10–24 µg/m3 measured in this study), these results have substantial public health implications.