If you want to dramatically lower the odds that you'll die of heart disease, go live someplace where public smoking is banned.

In a study of more than a million people, researchers found that even low levels of smoke from co-workers' cigarettes can substantially raise your risk of death from heart disease.

While you're packing to move, look for a place without much pollution, because a second study involving more than 9 million people in 126 counties across the U.S. has shown a direct correlation between the amount of carbon monoxide in the air and daily admissions to emergency rooms for heart problems.

Both studies are reported Monday in the American Heart Association's medical journal, Circulation.

In the first study, Dr. C. Arden Pope III from Brigham Young University in Arden, Utah and colleagues analyzed data on roughly 1.2 million adults that had been collected over 25 years as part of a study by the American Cancer Society.

We've known for a long time that smoking exposes your lungs to massive amounts of fine particulates and increases your risk of dying from heart disease, Pope told Reuters Health. Compared to active smoking, the dose of particulates to the lungs with passive smoking is much, much smaller, he added.

Even so, earlier studies have suggested surprisingly high rates of heart disease deaths from passive smoking, out of line with the much smaller dose of particulates. So, Pope said, he and his colleagues decided, We're going to take the largest data set available - from the American Cancer Society's Cancer Prevention Study II - and look at the effects of different increments of exposure to smoke and other pollutants on risk.

They discovered, Pope said, that the biggest increases in risk occur at lighter levels of exposure.

For example, compared to people who have never smoked, people who smoke up to 3 cigarettes per day increase their risk of dying from heart disease by 65 percent. Doubling or tripling the amount of cigarettes per day doesn't double or triple the risk, however; instead, for people smoking 8 to 12 cigarettes per day, the risk for heart disease death is increased to only 79 percent compared to never-smokers.

People smoking 18 to 22 cigarettes per day -- about a pack - have double the risk compared to never smokers.

Even more amazing, said Pope, was that compared to people who had never smoked and had no heavy exposure to smokers, passive smokers had a 20 to 30 percent higher risk of heart disease-related deaths. The strongest effect is seen in spouses of smokers.

The research team points out that the relationship between dose of tobacco particulates and the response in terms of increased risk is very steep. With light exposure, the result is substantial, Pope said, but with incremental increases in exposure, the increases in risk, while already high, start to rise more gradually.

This means, Pope said, that while it may do some good to smoke less, by far the biggest benefit is in not smoking at all. For example, he said, for smokers who are going to cut back by 3 cigarettes per day, the benefit of going from 20 to 17 is not nearly as large as the benefit of going from 3 to zero.

In some ways, this is good news, Pope commented. This adds to the plausibility that passive smoking and air pollution have a substantial effect on health. Cardiovascular disease is very common, he noted, so this impacts a lot of people.

We could get substantial public health benefits from reducing smoking and reducing passive smoking and exposure to air pollution, Pope said.

In the second study, Dr. Michelle Bell from Yale University in New Haven, Connecticut and colleagues studied how carbon monoxide levels in the air - mostly from traffic -- affect the numbers of people who show up in emergency rooms with heart problems.

They use hospitalization data from Medicare on more than 9.3 million enrollees, and pollution data from air quality monitoring stations in 126 urban counties across the United States where the Medicare recipients live.

The research team found a positive and statistically significant association between carbon monoxide levels on any given day and increased risks of hospitalization for a wide variety of heart problems.

Furthermore, this effect was evident even when daily 1-hour maximum carbon monoxide exposure was less than 1 part per million, well within the 35 part per million limit set by US regulatory agencies.

Although much of the current research on health and traffic-related air pollution focuses on particulate matter, our study indicates that ambient carbon monoxide and traffic may present a far larger health burden than suspected previously, Bell and her colleagues conclude.

SOURCE: Circulation 2009.