The harmful effects of secondhand smoke may be much greater than previously thought, according to a new study released today.
The research, published in the British Medical Journal, suggests that inhaling someone else's tobacco smoke may increase your risk of heart disease by up to 60 percent.
Some U.S. cities have banned smoking in bars and restaurants. But in most of the country, it's still legal.
Many communities insist there's not enough evidence that breathing in someone else's smoke does any harm, though this study is likely to change that.
"For the first time, we have hard evidence, physical evidence, of secondhand smoking getting into the bodies of nonsmokers and putting their health at risk," said Dr. Michael Fiore, professor of medicine at the University of Wisconsin Medical School.
"The important thing for the public is to get across the message that passive smoking really is a health hazard," said study author Martin Jarvis, a professor of epidemiology and public health at University College London in England.
"The scientific evidence is strong. The notion that it is still a 'controversy' is put about by the tobacco industry and its defenders in the face of clear evidence," he added.
The study followed more than 2,000 nonsmokers for 20 years.
Instead of simply asking study participants how much secondhand smoke they were exposed to both at home and at work, this study measured how much smoke they were actually breathing.
Researchers checked their blood for levels of cotinine, a byproduct of nicotine found only in tobacco smoke.
"What they found is that those individuals who had cotinine in their blood stream, but who were not smokers, had a much greater risk of heart attacks," Fiore said.
Responsible for 80,000 Heart Attacks
They discovered nonsmokers exposed to secondhand smoke had up to a 60 percent greater risk of heart attacks — twice as much as previous studies had reported. It suggests secondhand smoke may be responsible for up to 80,000 heart attacks each year in the United States.
Another surprise from this study: You don't have to inhale much secondhand smoke to start experiencing the harmful effects on the heart, blood and blood vessels.
"Those heart attacks occur with low levels of exposure and they occur very soon after people get exposed," said Stanton Glantz of the University of California at San Francisco, one of the country's leading researchers on the effects of tobacco.
Glantz said the study should come as a wake-up call to many communities
"In the past I had thought you had to get a lot of secondhand smoke. You had to be hanging out in a bar," he said. "And what this is showing is that just about any exposure you get is causing substantial increase in risk."
In short, Glantz said, just being near someone smoking a few cigarettes a day is almost like being a light smoker yourself. Secondhand tobacco smoke exposure can give you almost the same risk of a heart attack as if you smoked one to nine cigarettes a day.
Communities Reduce Smoking, Reap Benefits
Recent research has shown communities can reap immediate benefits from efforts to reduce smoking and exposure to secondhand smoke.
Another report published in the British Medical Journal showed heart attack rates dropped by 40 percent in Helena, Mont., after a smoke-free workplace law took effect in that city, said Andrew Hyland, an associate at the Roswell Park Cancer Institute in Buffalo, N.Y. "Rates increased back to pre-law levels when the regulation was rescinded," he said.
"Some of our most recent work shows that the level of indoor air pollution, a surrogate measure of secondhand smoke exposure, is about 85 percent lower in bars and restaurants that are required to be smoke-free by law compared to similar places where smoking is not restricted," he added.
Hyland conducted a study of air quality in seven major U.S. cities and found that New York bars had the cleanest air. New York City bars have been smoke-free since 2003.
In contrast, Hyland said, "The air quality in Washington, D.C., bars and restaurants, where smoking is permitted without restriction, ranked last with levels of pollution nearly 16 times greater than in New York City."
Hyland hopes the new data showing the risk of heart attack almost doubled by exposure to secondhand smoke encourages more communities to follow New York's lead.
ABC News' John McKenzie and Joanna Schaffhausen contributed to this report.