Even small amounts of smoke — such as from smoking a few cigarettes a day, inhaling someone else’s tobacco smoke or breathing polluted air — increase the risk of death from cardiovascular disease (CVD), researchers report in Circulation: Journal of the American Heart Association.
In an analysis of prospective data on more than 1 million adults, researchers found that the exposure-response relationship was steepest at relatively low levels of exposure. The risk continued to increase, but leveled off with increasing levels of smoking.
The major findings were:
* The largest incremental boost in risk of CVD death came with smoking three or less cigarettes a day, which increased the risk by about 64 percent.
* Those smoking 8-12 cigarettes per day (about a half pack) had a 79 percent increased risk of CVD death.
* Those smoking 18-22 cigarettes per day (about a full pack) had approximately a 100 percent increased risk of CVD death.
* Breathing moderate to high levels of ambient air pollution and secondhand smoke, with estimated exposures at far less than smoking one cigarette a day, still increased risk of CVD death by approximately 20 percent to 30 percent compared to those without exposure.
“The evidence in this integrated analysis suggests that there are no apparent safe levels of exposure to cigarette smoke or ambient air pollution,” said C. Arden Pope III, Ph.D., Mary Lou Fulton Professor at Brigham Young University in Provo, Utah. “This may be due to the fact that even with relatively low levels of smoke there are adverse biologic responses such as inflammation, increased platelet activation and altered cardiac function.”
Researchers collected data from the American Cancer Society Cancer Prevention Study II (ACS CPS-II) and integrated it with studies of secondhand smoke andair pollution. The large ACS CPS-II data set allowed researchers to pinpoint excess risk of cardiovascular death associated with relatively small increments of cigarette smoking while controlling for other risk factors such as education, marital status, body mass, alcohol consumption, occupational exposures and diet.
Researchers plotted relative risks of cardiovascular death from increments of cigarette smoking along with comparison estimates for secondhand smoke and air pollution over estimated inhaled doses of fine particulate matter.
“Past studies have established that active cigarette smoking exposes human lungs to extremely large amounts of fine particulate matter and is a major independent contributor to cardiovascular disease,” Pope said. “Our analysis illustrates that it doesn’t require extreme exposure to have significant cardiovascular effects. Even passive exposures to ambient air pollution and secondhand smoke contribute to significant increases in cardiovascular mortality.”
Reasonable efforts should be made to avoid secondhand smoke, and public policy must improve air quality — both of which will have a positive impact on public health — Pope said.
“A critical finding of our study is that smoking is unhealthy even at small amounts,” Pope said.
“Reducing the amount one smokes does some good, but the biggest benefits come from stopping completely.”
In an accompanying editorial on this study and one on carbon monoxide exposure, Annette Peters, Ph.D., from the German Research Center for Environmental Health, Institute of Epidemiology, notes that the research “makes an important contribution of the assessment of the role of the environment for cardiovascular health.” Together, the studies:
* highlight the consistently emerging evidence that both indoor and outdoor air quality is a modifiable risk factor for cardiovascular disease;
* provide consistent evidence for health effects of particulate matter;
* note that the health effects of low dose smoking, secondhand smoke and air pollution are probably still underestimated by decision makers around the world; and
* suggest that air quality regulation should include regular reassessment of emerging and existing air quality measures in addition to a standard for particulate matter smaller than 2.5 ?m (PM2.5).
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