MEDICINE / HEART DISEASE : Secondhand Smoke’s Damaging Effects Analyzed : Cardiovascular system is harmed in several ways, researchers say. Impact of exposure to small amounts is greater in nonsmokers, they say.

In the most comprehensive report of its kind, UC San Francisco researchers have detailed the exact mechanisms by which secondhand smoke can damage the heart and circulatory system.

The report in today’s Journal of the American Medical Assn. presents new research by UC San Francisco and an analysis of the most recent scientific studies on secondhand smoke. It describes numerous pathways taken by the components of tobacco smoke that can lead to heart disease. Moreover, the researchers argue that even a small quantity of secondhand smoke causes more cardiovascular damage in nonsmokers than in smokers.

The cardiovascular analysis is significant because most government regulations regarding secondhand smoke have been based on evidence that it can cause cancer; the Environmental Protection Agency has deemed it a Class A carcinogen. But the evidence regarding the effects of a small amount of secondhand smoke on heart disease has been controversial.

“We not only know that secondhand smoke causes heart disease, but we are now getting a very good idea of how it causes heart disease,” said the paper’s co-author, Stanton A. Glantz of UC San Francisco.

The evidence that secondhand smoke causes heart damage may accelerate the move toward smoking restrictions, said Scott D. Ballin, of the Coalition on Smoking or Health, which consists of the American Heart Assn., American Lung Assn. and American Cancer Society.

“The scientific evidence continues to accumulate that says there is this connection to secondhand smoke and cardiovascular disease,” Ballin said. “It builds a stronger and stronger case about why we need public policy regulations.”

The Occupational Safety and Health Administration has proposed a rule to ban workplace smoking--a proposal fiercely challenged by the tobacco industry. The industry has lobbied to limit the reach of secondhand smoking laws, charging that the science on secondhand smoke is shaky at best.

In a statement issued Tuesday, tobacco industry leaders said that Glantz and co-author William W. Parmley ignored some studies that show no association between secondhand smoke and heart disease and failed to acknowledge their own conclusion that the risk of dying of heart disease as a result of secondhand smoke is small.

“What Glantz (and) Parmley have done in this article is to discount the available real-world data and rely instead on a number of theories concerning how exposure to environmental tobacco smoke might increase the risk of heart disease,” the statement said.

Until recently, most of the evidence that passive smoke causes heart disease in nonsmokers was based on epidemiological studies that merely showed an association between people routinely exposed to secondhand smoke and an increased risk of heart disease. The analysis published today consists of recent clinical, laboratory and epidemiological studies that demonstrate the underlying physiological and biochemical changes from ingestion of environmental tobacco smoke.

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The report, which featured some of Glantz and Parmley’s research at the Cardiovascular Research Institute at UC San Francisco, concluded that secondhand smoke damages the heart by:

* Reducing the body’s ability to deliver oxygen to the heart and inhibiting the heart’s ability to effectively use oxygen.

* Increasing the amount of lactate--a salt derived from lactic acid--in blood, making it more difficult to exercise.

* Activating blood platelets, which increases the risk of blood clots and damages the lining of the coronary arteries.

* Aggravating tissue damage after a heart attack.

“About four years ago, what was happening in the heart could only be suggested. What’s different today is that the studies have been done to show those things actually happen,” Glantz said.

Many elements in tobacco smoke contribute to heart damage, the authors said.

“The effects of secondhand tobacco smoke on the cardiovascular system are not caused by a single component of the smoke, but rather are caused by the effects of many elements, including carbon monoxide, nicotine, polycyclic aromatic hydrocarbons, and other . . . elements in the smoke,” they said.

Nicotine was found to activate blood platelets, which can lead to clotting and the development of lesions on the artery walls. The carbon monoxide in environmental tobacco smoke was found to compete with oxygen for binding sites on red blood cells, thus limiting the oxygen delivered to the heart.

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Moreover, the researchers said, the same amount of secondhand smoke causes more damage to nonsmokers than to smokers. Among smokers, the cardiovascular system appears to adapt to limit the damaging effects.

“The doses of secondhand smoke are small compared to what smokers get, but the effects aren’t,” Glantz said.

This is important, Glantz and Parmley said, because the tobacco industry often says that the amount of secondhand smoke inhaled by the typical nonsmoker is equivalent to only one cigarette smoked per day.

But even that amount can damage the heart, said Dr. Homayoun Kazemi, a professor of medicine at Harvard University and a researcher on secondhand smoke.

“A major message of the study is that secondhand smoke cannot be equated with quantities of smoke that the cigarette smoker inhales. They are showing even small amounts of tobacco smoke are having greater effects on the nonsmoker’s system.”