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Winter/Spring 2010 Vol. 10 Number 1

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Clearing the Air About Smoking Bans

New Report Dispels Uncertainties About Secondhand Smoke and Bans

No one seriously doubts that smoking harms one's heart and lungs, but just how dangerous is smoke inhaled secondhand by nonpuffing bystanders? It seems obvious to many public health officials and proponents of smoke-free policies that breathing air laden with chemicals from tobacco smoke is harmful. Skeptics of the risks have pointed to limitations in researchers' abilities to measure nonsmokers' exposures and to conclusively pinpoint what amounts are necessary to trigger heart attacks. This view recently got harder to sustain, however, in light of a report from the Institute of Medicine released in October. The report concludes that the science not only shows the health risks to nonsmokers but also underscores smoking bans' effectiveness in reducing these risks.

"It's clear that secondhand smoke can cause heart disease and that smoking bans reduce the risk of heart attack in nonsmokers as well as smokers," said environmental health scientist Lynn Goldman of Johns Hopkins' Bloomberg School of Public Health in Baltimore and chair of the committee that wrote the report.

Despite their variations and limitations, studies of environmental tobacco smoke exposure consistently show that breathing secondhand smoke increases the risk of coronary heart disease in nonsmokers, the committee noted. The more people breathe in, the greater their risk.

There is no direct evidence that a brief encounter with secondhand smoke could precipitate a heart attack, but the committee called "compelling" the indirect evidence indicating that even short exposures could affect someone already at risk. Results of studies looking at smoke from factories and other pollution sources suggest that even a relatively brief exposure to millions of tiny pollutant particles can constrict blood vessels and increase clotting, both potential precursors to a heart attack. Fine particles are a major component of secondhand smoke, too. Many people are not aware they have heart disease until their first heart attack, so avoiding secondhand smoke is generally a prudent move, said physician and committee member Neal Benowitz of the University of California, San Francisco.

Pinpointing the effects of smoke-free policies is more challenging, and some of the committee members were skeptical that they would be able to draw firm conclusions. The totality of the evidence proved convincing, said statistician Stephen Fienberg of Carnegie Mellon University in Pittsburgh. Eleven key studies assessed rates of heart attacks in communities that enacted smoking bans and consistently found that the rates went down. Although the drops might be explained to some extent by improvements in smokers' health, two studies distinguished whether patients were nonsmokers or smokers and saw the number of heart attacks go down in both groups.

The declines ranged from 6 percent to 47 percent across the studies. Given the studies' variations and the limited data on people's exposures to secondhand smoke before and after the bans, the committee could not precisely determine the magnitude of the effect. "Whether the risk reduction is less than 10 percent or greater than 40 percent, either way it means significantly fewer deaths," Goldman said.

Upon its release, the report was quickly picked up by individuals and groups urging their elected officials to pass smoking ordinances. Although the majority of the states and largest metropolitan areas have enacted some form of smoke-free policies, about 43 percent of nonsmoking children and 37 percent of nonsmoking adults are still exposed to secondhand smoke. But fewer will be in 2010; two-thirds of voters in St. Louis approved a countywide ban on smoking in public venues last November. Last December, Michigan became the 38th state to ban smoking in at least some public places, and Kansas took a big step toward becoming the 39th in February this year when a ban passed the state legislature. — Christine Stencel

Secondhand Smoke Exposure and Cardiovascular Effects: Making Sense of the Evidence. Committee on Secondhand Smoke Exposure and Acute Coronary Events, Board on Population Health and Public Health Practice, Institute of Medicine (2010, 240 pp.; ISBN 0-309-13839-6; available from the National Academies Press, tel. 1-800-624-6242; $39.00 plus $5.00 shipping for single copies).

The committee was chaired by Lynn R. Goldman, professor of environmental health sciences, Bloomberg School of Public Health, Johns Hopkins University, Baltimore. The study was funded by the U.S. Centers for Disease Control and Prevention.

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Copyright 2010 by the National Academy of Sciences