The first direct medical evidence that secondhand smoke can damage the lungs of non-smokers has been produced by an international team led by researchers at Harvard University.
The team performed autopsies on the 30 non-smoking women and found that the lungs from the wives of smokers contained a "significantly higher" number of precancerous abnormalities -- such as cellular proliferation and damage -- than did lungs from the wives of non-smokers.
Previous studies showing a higher incidence of lung cancer among wives and children of smokers have been based on statistical evidence and suggest that at least 4,000 people die from lung cancer each year as the result of inhaling secondhand smoke.
But the tobacco industry has argued that the reported link between lung cancer and passive smoking could come from biases in the collection of that epidemiological data.
The new study, reported in Wednesday's Journal of the American Medical Association, appears to show that those statistics were not biased, proponents say.
"It is a pathfinding study," said Dr. Morton Lippman, a professor of environmental medicine at the New York University Medical Center who recently chaired an Environmental Protection Agency panel evaluating the hazards of secondhand smoke. A preliminary version of that risk assessment, released in June, concludes that environmental tobacco smoke causes lung cancer in non-smoking adults, increases the risk of respiratory infection in children and exacerbates symptoms in children with asthma.
"We have taken the position for several years that the epidemiological data are very convincing," added Dr. Norman Edelman, a pulmonary specialist at the Robert Wood Johnson Medical School in New Brunswick, N.J., and consultant to the American Lung Association.
"But what this does," he said of the new study, "is give us visual evidence, biological confirmation of that. That's important both in terms of science and in terms of public perception. . . . It doesn't tell us anything we don't know, but in science and public policy we like to confirm what we know from different points of view."
The tobacco industry, however, immediately challenged the study. Because of the small number of subjects involved in the study, said Tom Lauria, a spokesman for the Tobacco Institute, the data "is likely to be subjected too many biases and confounding factors. . . .
"This is basically an epidemiology study with an autopsy attached, but the possibility for error is much greater because you are talking about a biological finding. So the usefulness of this study is many times less than what you would expect."
But Dr. Edelman noted that for years the tobacco industry made similar arguments about the epidemiological data linking smoking itself to lung cancer.
"They put up that smoke screen for years and years and years" before researchers demonstrated that smoking caused cancer in animals, he said. "There's a kind of parallel now in that this provides the same kind of visual evidence" as the studies in animals.
According to the American Heart Association, 50 million non-smoking adults over the age of 35 are exposed to secondhand smoke and about 50 percent of all American children live in families with one or more smokers.
A June AHA report estimated that, in addition to its effects on lung cancer, secondhand smoke could be a contributing factor in the heart-disease deaths of 40,000 non-smoking Americans every year.
In obtaining the new results, a team headed by Dr. Dimitrios Trichopoulos, an epidemiologist at the Harvard School of Public Health, studied lung tissue obtained from autopsies of 400 people who died in Atica, Greece, between 1986 and 1990. Such autopsies are mandatory in Greece when a death is due to external causes, such as violence or accident, or has resulted from sudden illness. None of the subjects died of lung cancer or respiratory disease.
The physicians determined the total number and severity of the abnormalities in the lung tissue of each subject and then compared it with the history of the subject. The researchers found that a significantly larger number of abnormalities were present in the lungs of the wives of smokers than in the wives of non-smokers. The number of abnormalities could not be linked to any other factor.