Risk of Cardiovascular disease - smoking 3-cigarettes per day or exposure to secondhand smoke..

September 4, 2009 - Risk of cardiovascular disease (CVD) increased 64 percent by smoking three cigarettes a day. Risk doubled by smoking a pack a day, according to data on more than one million adults prospectively collected by the American Cancer Society, as part of the Cancer Prevention Study II of 1982.

Using this database, Dr C Arden Pope (Brigham Young University Provo, UT) and colleagues calculated adjusted relative risks of mortality according to an estimated average daily dose of fine particulate matter (PM) from active cigarette-smoke inhalation, as well as the PM doses from secondhand cigarette-smoke exposure and from exposure to air pollution.

The researchers report: "There were substantially increased cardiovascular mortality risks at very low levels of active cigarette smoking and smaller but significant excess risks even at the much lower exposure levels associated with secondhand cigarette smoke and ambient air pollution. Our results suggest that the exposure-response function is relatively steep at very low levels of exposure, flattening out at high exposure levels."

The researchers note several limitations of the study, among them the large exposure gap between ambient air pollution, secondhand-smoke exposure, and active smoking. And, the authors say, there are no prospective cohort or related studies of long-term exposure across the range of exposure that would fill this gap.

Even with its limitations, the study findings have important public-health implications, Pope's team comments. Most studies of the effects of fine PM on cardiovascular disease risk have been conducted in areas where the annual average PM concentrations rarely exceed 30 µg/m3. Recent estimates indicate average concentrations of particulate air pollution in urban areas of China, India, and other developing countries often exceed 100 µg/m3.

PAPER: Cardiovascular Mortality and Exposure to Airborne Fine Particulate Matter and Cigarette Smoke. Shape of the Exposure-Response Relationship, C. Arden Pope III PhD, Richard T. Burnett PhD, Daniel Krewski PhD, Michael Jerrett PhD, Yuanli Shi MD, Eugenia E. Calle PhD, and Michael J. Thun MD, Circulation. 2009 Published online before print August 31, 2009, ABSTRACT...

Relatively low levels of fine particulate exposure from either air pollution or secondhand cigarette smoke are sufficient to induce adverse biological responses increasing the risk of cardiovascular disease mortality.

Reference: Only three cigarettes a day significantly increases cardiovascular disease risk, Martha Kerr, 9/3/2009.