The heart just doesn't like smoking, no matter who's doing it.

That's the take-home message of a review of research about secondhand smoke's cardiac toll. The report — published in Circulation — documents a long list of heart hazards from secondhand smoke.

Wisp for wisp, secondhand smoke's heart damage often rivals that of active smoking, and even a little exposure may have an impact, says the review by Joaquin Barnoya, MD, MPH, and colleagues.

Secondhand smoke's heart effects are "rapid and large," like those of air pollution, say Barnoya and colleagues. How large? On average, the heart effects of even brief secondhand smoke exposure are about 80 percent to 90 percent as large as that from chronic active smoking, they say.

An 'Exquisitely Sensitive' Heart

Smokers' hearts bear the biggest burden. They are exposed to more toxins from smoking than people who only get secondhand smoke. But that doesn't appear to make much difference to the heart, says the review.

Passive smoke has a much larger effect on the heart than would be expected from a comparison of the dose of toxins, they write.

Despite the fact that the dose of smoke delivered to active smokers is 100 times or more than that delivered to a passive smoker, the risk of heart disease for smokers is more than two-thirds higher compared with a third higher for passive smokers, says the review.

The cardiovascular system may be "exquisitely sensitive to the toxins in secondhand smoke," write the researchers.

Growing Evidence of the Dangers of Secondhand Smoke

The researchers say that the effects of passive smoke are numerous and interact with each other, increasing the risk of heart disease. Here are some of the heart hazards that the review linked to secondhand smoke.

— Increased blood clotting ability
— Increased blood vessel wall abnormalities
— Higher risk of atherosclerosis (hardening of the arteries)
— Lower levels of HDL "good" cholesterol (even in children)
— More buildup of LDL "bad" cholesterol in artery walls
— Higher blood levels of markers of inflammation that are inked to heart disease and blood vessel wall plaque buildup
— Increased source of cell-damaging free radicals
— Lower levels of antioxidants, which fight free radicals

Evidence about secondhand smoke's heart dangers has been growing since the mid-1980s, say the researchers.

"Secondhand smoke increases the risk of heart disease by [about] 30 percent, accounting for at least 35,000 deaths annually in the United States," they write.

Brief Exposure Can Have an Impact

Secondhand smoke may register on the heart in a short time, the review shows.

"The effects of even brief (minutes to hours) passive smoking are often nearly as large (averaging 80 percent to 90 percent) as chronic active smoking," says the review.

For instance, one study exposed 12 men to six hours of secondhand smoke — about what someone might get from an evening in a smoky bar. For the next 24 hours, the men's levels of HDL "good" cholesterol were significantly lower than before the experiment.

In another study, healthy men breathed secondhand smoke from 15 cigarettes for an hour in an unventilated room. During that hour, the men had a significant increase in aortic arterial stiffness — an early marker of blood vessel wall abnormalities that increases heart disease risk.

The stiffness started after just 15 minutes, then hit and maintained its peak at 30 minutes.

Antioxidant Defense?

Antioxidant supplements might help replenish antioxidant levels lowered by secondhand smoke, says the review.

However, that "probably will not prevent the [heart] damage associated with secondhand smoke because such supplements do not seem to reduce the risk of heart disease in general," say the researchers.

Quitting smoking and limiting exposure to secondhand smoke may help your health. Smoking has been tied to many other health problems besides heart disease, including cancer, erectile dysfunction, sudden infant death syndrome (SIDS), asthma, infertility, and problems in pregnancies.

Mechanisms May Work Together

The mechanisms behind secondhand smoke's heart damage may gang up, egging each other on to raise heart disease risk, write Barnoya and colleagues.

Barnoya worked on the review while on staff at the University of California, San Francisco. Now, he works at the Unidad de Cirugía Cardiovascular de Guatemala.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Barnoya, J. Circulation, May 24, 2005; vol 111. News release, American Heart Association. WebMD Feature: "10 Overlooked Reasons to Quit Smoking." WebMD Medical Reference from Healthwise: "Quitting Tobacco Use: How is Smoking Harmful?"