DALLAS (AP) -- The American Heart Association has updated its guidelines for preventing heart attacks and strokes, listing secondhand smoke as a risk factor for the first time and recommending that people get screened for risk factors beginning at age 20.

Also, a daily dose of aspirin, previously recommended only for those who have already had heart attacks and strokes, is now suggested for people who have been found to have at least a 10 percent risk of a heart attack in the next decade.

And to address the nation's growing obesity problem, the heart association adopted a simpler alternative to the body-mass index: a waistline measurement. Simply put, men should have a waistline of 40 inches or less; for women, 35 inches or less.

"It's turned out that waist circumference is as good a predictor of risk as body mass index," said Dr. Sidney C. Smith, the association's chief science officer.

The revised "Guide to the Primary Prevention of Cardiovascular Diseases" was published in Tuesday's issue of the journal Circulation. The guidelines have not been updated since they were first published in 1997.

"The emphasis is on prevention. We know a lot about cardiovascular disease. We know what causes it, we know how to prevent it," said Dr. Thomas A. Pearson, a professor at the University of Rochester School of Medicine and chairman of a committee that revised the guidelines.

For the first time, the new guidelines urge people age 20 and older to meet with a doctor every five years to assess risk factors such as smoking, family medical history and blood pressure. Previously, the heart association did not give an age at which patients should first be screened for their risk of heart disease.

People age 40 and older should be screened for additional risk factors, including high cholesterol levels, the heart association said.

For the first time, secondhand smoke was added to the list of risk factors, which already included smoking itself.

The guidelines combine the latest findings from an array of studies.

The new guidelines drop passages in the 1997 edition that said hormone supplements and antioxidant vitamins might reduce the risk of heart attacks and strokes. More recent research - some of it released just last week - has called those assertions into questions.

Doctors applauded the idea of screenings for heart disease, the nation's leading health problem.

"These new recommendations should benefit the entire nation. Certainly prevention is the key," said Dr. Robert Frankel of Maimonides Medical Center in New York City. "I think this will heighten awareness. Having earlier detection systems certainly will identify those patients at risk."

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