You eat right, exercise and don't smoke, but you're drawn to the milieu of smoky night clubs. Is the secondhand smoke you breath harmful?

If so, how much smoke does it take to cause disease -- and if you quit going to clubs does your risk drop? No one knows the answers to those questions, which might help explain why the idea of a statewide smoking ban in bars and restaurants remains stalled in Minnesota. Yet there's also wide agreement among medical experts that secondhand smoke contains carcinogens and other toxins that can cause lung cancer and heart disease. "Based on our understanding of how cancer is caused, any exposure causes some risk," said Terry Pechacek, a scientist in the federal Centers for Disease Control and Prevention (CDC) Office of Smoking and Health. "Are we talking about one in a million chances, one in 10 million chances? The risk can be very small." Tobacco smoke that enters the body can change any cell it touches, Pechacek said. "Once a cell has been converted by exposure -- a single cell of the trillions of cells in the body -- then you're playing roulette. Will the body systems kill that [carcinogen] off before it becomes a life-threatening tumor? There's a whole lot of uncertainty." A recent Minnesota study shows how potent environmental tobacco smoke can be. Eleven nonsmoking volunteers who spent four hours in a smoky casino had high levels of two tobacco-related cancer agents in their urine, said Kristin Anderson, an epidemiology professor at the University of Minnesota and lead author of the study. Could one such exposure in a smoky bar damage body cells? The answer, said Pechacek of the CDC, probably is yes. "Would that mean that it would turn into a life-threatening cancer? Unlikely, but we're dealing in a probabilities game there. No exposure is always the safest route." Cancer risk is cumulative. "The longer the exposure, the higher the risk, but we're unable to say at what level it makes a critical difference," Anderson said. "On the other hand, we also can't say what level is safe." Anderson's study is significant because it shows that people exposed to tobacco smoke in a public setting -- not in a lab or other controlled environment -- "are actually taking up and absorbing carcinogens in the smoke, which is a pretty powerful statement," said Stephen Babb, a consultant to the CDC on smoking and health. Forty years after the first Surgeon General's report documented the health risks of smoking, there's little disagreement that cigarette smoke can cause lung cancer and heart disease in nonsmokers. Nearly every agency with an interest in the topic supports that premise: the U.S. Surgeon General, the U.S. Environmental Protection Agency, the National Academy of Sciences, the National Institutes of Health and the Occupational Safety and Health Administration. The CDC estimates that 3,000 nonsmokers die of lung cancer caused by secondhand smoke each year. An additional 35,000 die of heart disease, also from secondhand smoke, the CDC says; other estimates have been as high as 62,000. The knowledge that secondhand smoke can cause lung cancer, heart diseases and other conditions has prompted states, cities, even countries to ban smoking in bars, restaurants, other public places and workplaces. California, New York, Connecticut, Delaware and Maine have gone smoke free, as have Ireland (effective next week) and Sweden (next year). Norway, where cigarettes cost $8.50 a pack, will go smoke free June 1. In a country with a population comparable to Minnesota's, secondhand smoke kills 350 to 550 people a year, its health ministry says. In Minnesota, 38 communities have proposed smoking bans but only three cities, Moose Lake, Cloquet and Duluth, and one county, Olmsted, have approved them. A statewide smoking ban died in the Minnesota Legislature last week. It would have banned smoking in workplaces not covered by existing bans, including bars and restaurants. Growing evidence of harm In 1975 the Minnesota Legislature enacted the Clean Indoor Air Act, the first law of its kind. Its purpose was to "protect the public health, comfort and environment" by limiting smoking to designated areas in public places and at public meetings. Under the law, business proprietors who choose to designate a smoking area must minimize the "toxic effect" of smoke on people in adjacent nonsmoking areas. Single-room establishments are allowed to designate one side of the room as nonsmoking. It soon became clear, in Minnesota and elsewhere, that smoke doesn't stay on its side of the room. In 1986, the U.S. Surgeon General issued its first report on secondhand smoke, concluding that breathing in tobacco smoke, like smoking itself, can cause disease, including lung cancer, in nonsmokers. The smoker's decision to smoke "should not interfere with the nonsmoker's choice for an environment free of tobacco smoke," Otis R. Bowen, then-secretary of health and human services, wrote in the report. Much of the official and medical concern about secondhand smoke has focused not on the patrons of bars and restaurants, but on the people who work in them. Some workers breathe secondhand smoke for hours day after day. Tobacco smoke contains more than 4,000 chemicals, and 250 of them are known to be toxic or cancer-causing, according to the National Toxicology Program, a federal program that tests chemicals. A Boston study found that the level of tobacco smoke in bars was four to six times higher than in office workplaces and more than four times higher than in homes with at least one smoker. Children are significantly harmed by secondhand smoke, especially if a parent smokes. Research shows that children who live with smokers have a higher incidence of pneumonia, bronchitis, ear infections and asthma attacks. Because homes cannot be regulated, public health campaigns encourage parents to quit smoking or smoke outside. In Minnesota 70 percent of households with children have banned smoking in the home, but in smokers' households only only 47 percent were smoke free, according to a statewide survey in 2000. Risk of heart disease Secondhand smoke also causes heart disease, experts say. While exposure that leads to cancer is cumulative, the heart disease risk happens quickly and goes away quickly, Pechacek said. "Lab studies show that even 20 or 30 minutes of exposure causes the biological changes that increase risk." Chemicals in smoke cause red blood cells and the blood-clotting molecules called platelets to become sticky, Pechacek said. If a nonsmoker had some blockage in an artery -- as many people in their 40s and 50s do -- a blood clot could cause a heart attack or stroke, he said. Could a person in his 40s or 50s, with some blockage, have a heart attack from spending an evening in a smoky bar? "There are cardiologists, there are respected cardiovascular researchers who say 'yes' to that," Pechacek said. The good news is that health risks decline when tobacco smoke is removed, he said. In California, which bans smoking in restaurants and bars, bartenders' lung functioning improved a few weeks after that state's smoking ban took effect, a study found.

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