A burning cigarette is a health risk to everyone in the same room. The scientific evidence of tobacco hazards is strongest for smokers. However, research reveals that regular exposure to secondhand tobacco smoke also threatens the health of nonsmokers. 37,000 to 40,000 people die from heart and blood vessel disease caused by other people's smoke each year.

Secondhand smoke, also known as environmental tobacco smoke, is a mixture of sidestream smoke from the burning end of a cigarette, pipe or cigar and smoke exhaled from the lungs of smokers. About half the smoke generated from a cigarette is sidestream smoke. Sidestream smoke contains essentially the same compounds as does smoke inhaled by the smoker. Secondhand smoke contains substances that irritate the lining of the lung and other tissues. It promotes genetic changes in cells and interferes with cell development, raising the risk of certain cancers.

• A 1996 study published in the Journal of the American Medical Association found detectable levels of serum cotinine - a breakdown product of nicotine - in nearly 9 of every 10 nonsmokers in a large, nationally representative sample.

Research has linked secondhand smoke to cardiovascular disease and many other chronic disorders.

Secondhand smoke and cardiovascular disorders

Researchers are gathering evidence of the effect of secondhand smoke on the heart and blood vessels. A small Japanese study looked at the effects of secondhand smoke on circulation in young men. Exposure to secondhand smoke was associated with reduced blood flow through the arteries feeding the heart. One theory behind the finding is that secondhand smoke affects the function of the cells that line the heart and blood vessels.

• A study of Swedish women and men ages 45 to 70 found a higher risk of nonfatal heart attack among those whose spouses smoked 20 or more cigarettes a day than among people who were not exposed to secondhand smoke from their spouses. The risk was higher for women.
• A study of 32,000 women who were nurses found that regular exposure to secondhand smoke doubled their risk of a heart attack. The study compared outcomes among nurses who reported regular exposure to secondhand smoke at work and home with those who reported no exposure. The study found the association between heart attacks and secondhand smoke after accounting for many other cardiovascular risk factors such as high blood pressure or high cholesterol.