NEW ORLEANS — People with low cholesterol and no big risk for heart disease dramatically lowered their chances of dying or having a heart attack if they took the cholesterol pill Crestor, a large study found.

The results, reported Sunday at an American Heart Association conference, were hailed as a watershed event in heart disease prevention. Doctors said the study might lead as many as 7 million more Americans to consider taking cholesterol-lowering statin drugs, sold as Crestor, Lipitor, Zocor or in generic form.

"This takes prevention to a whole new level, because it applies to patients who we now wouldn't have any evidence to treat," said Dr. W. Douglas Weaver, a Detroit cardiologist and president of the American College of Cardiology.

The study also gives the best evidence yet for using a new test to identify people who may need treatment, according to a statement from Dr. Elizabeth Nabel, director of the National Heart, Lung and Blood Institute. The new research will be considered by experts reviewing current guidelines.

However, some doctors urged caution. Crestor gave clear benefit in the study, but so few heart attacks and deaths occurred among these low-risk people that treating everyone like them in the United States could cost up to $9 billion a year — "a difficult sell," one expert said.

About 120 people would have to take Crestor for two years to prevent a single heart attack, stroke or death, said Stanford University cardiologist Dr. Mark Hlatky. He wrote an editorial accompanying the study published online by the New England Journal of Medicine.

"Everybody likes the idea of prevention. We need to slow down and ask how many people are we going to be treating with drugs for the rest of their lives to prevent heart disease, versus a lot of other things we're not doing" to improve health, Hlatky said.

Statins are the world's top-selling drugs. Until this study, all but Crestor have already been shown to cut the risk of heart attacks and death in people with high LDL, or bad cholesterol.

But half of all heart attacks occur in people with normal or low cholesterol, so doctors have been testing other ways to predict who is at risk.

One is high-sensitivity C-reactive protein, or CRP for short. It is a measure of inflammation, which can mean clogged arteries as well as less serious problems, such as an infection or injury. Doctors check CRP with a blood test that costs about $80 to have done.