Risks for women: passive smoke and obesity.

For a quarter of a century, more than 120,000 registered nurses have been assisting physicians in a very personal way. As participants in an ongoing study, they've bared details of their own medical and life histories to flesh out a better understanding of health risks faced by U.S. women generally.

The two latest analyses from the nurses' survey, both published this week, quantify the health fallout of two of the most important lifestyle hazards confronting women--breathing the cigarette smoke of others, which can foster heart disease, and obesity, which increases the risk of stroke.

New estimates of both risks are appreciably higher than earlier reports had indicated.

To study the effects of secondhand smoke, Ichiro Kawachi and his colleagues at Harvard Medical School in Boston focused on a subset made up of 32,000 nurses who, as of 1982, had never smoked or exhibited signs of heart disease. At that time, the researchers asked the 36- to 61-year-old women how often they encountered smoke at home and at work. They also tallied how many years each woman had shared her home with a smoker. Overall, 80 percent of the women reported breathing secondhand smoke.

In the May 20 Circulation, the Harvard team reports that over the succeeding decade, 135 women (0.52 percent) who had reported occasional or regular exposure experienced a heart attack, compared to only 17 (0.28 percent) who said they had never encountered secondhand smoke.

Though a number of studies have linked heart disease to passive smoking, Kawachi says, "there has been a persistent criticism that these studies had not controlled for many things that otherwise might explain the association," such as poor diet or a family history of high blood pressure. "So we tried to address everything we could think of," he says, "and still we found that regular passive smokers were at about twice the risk of heart attack as those not exposed."

Even women reporting only occasional exposure to cigarette smoke had a 60 percent higher risk than those who reported no exposure. Earlier studies suggested that regular secondhand smoke might elevate heart attack incidence in nonsmokers by only 30 or 40 percent.

Controlling for so many dietary, health, and other factors makes the new study "quite strong," notes epidemiologist Genevieve Matanoski of the Johns Hopkins University School of Public Health in Baltimore. She says the new risk estimates could be "a little exaggerated," however, if the nurses with other predisposing risks for heart disease unwittingly overestimated how much smoke they were exposed to.

Moyses, Szklo, also of Johns Hopkins, says the nurses' data "are consistent with our own--that people exposed to environmental tobacco smoke are more likely to have atherosclerosis, the pathological process underlying heart attacks." Exposure to secondhand smoke causes a premature atherosclerotic thickening of the wall of the carotid artery, he's found.

Though the Surgeon General has estimated that 3,000 passive smokers in the United States die from lung cancer each year, deaths due to secondhand smoke may climb another 30,000 if the new heart attack risk figures hold up, Kawachi says.

The good news is that the already increasing limits on public smoking should be bringing about a decline in atherosclerotic risks for passive smokers.

For the study linking strokes and obesity, researchers began collecting data on 116,759 of the nurses in 1976, when the women were 30 to 55 years old. Through 1992, the team tracked general health, lifestyle, weight changes since age 18, and incidence of stroke.

Obesity appeared to increase a woman's chances of having an ischemic stroke, a loss of blood flow to part of the brain. Though seldom fatal, these strokes can prove debilitating. A woman 5 feet 6 inches tall who had gained more than 22 pounds since age 18 was nearly twice as likely to have a stroke as a woman who had kept her weight down, says study leader Kathryn M. Rexrode of Brigham and Women's Hospital in Boston. When compared to the leanest women, those who were most obese faced 2.5 times the risk of ischemic stroke, the researchers report in the May 21 Journal of the American Medical Association.

All cigarette smokers faced a heightened risk of ischemic stroke, regardless of their weight.

Obesity's link to the more dangerous, hemorrhagic strokes, in which a burst blood vessel causes bleeding in the brain, was inconclusive.

Differentiating between these types of strokes marks a departure from past studies. Earlier studies that focused simply on deaths caused by any stroke overrepresented hemorrhagic strokes--thereby largely missing obesity's role in ischemic ones, the authors say.

Also unusual for a stroke study, this one included women with high blood pressure or diabetes, pathways by which obesity can cause harm. Indeed, Rexrode says, "the way obesity is causing strokes is through higher blood pressure and other metabolic effects."