The National Institutes of Health, sponsor of the Women's Health Initiative, decided to halt the estrogen study in March 2004, more than a year and a half early, because of a higher risk of stroke in estrogen users. In June 2004, a study of women 65 to 79 in the estrogen trial reported that the hormone could increase older women's risk of dementia.

The study, which was reported in the Archives of Internal Medicine, did find fewer heart attacks and coronary deaths in the women in their 50s who took estrogen, but because there were so few cases, the finding was not statistically significant. It could have been chance.

Only when the scientists combined cases of heart attacks, coronary deaths, angioplasty and bypass surgery did the difference between estrogen and a placebo become statistically significant among women in their 50s. But no one is advising any postmenopausal woman to take estrogen solely to prevent heart disease, as had been the custom for years.

"Although this finding does suggest a lower heart disease risk, you have to take all the risks and benefits together," says lead author Judith Hsia, a George Washington University cardiologist.

Higher Risk of Stroke

Hsia's study was part of the Women's Health Initiative, which also included a parallel study of estrogen plus progestin vs. placebo. Overall, estrogen alone seems to be safer than estrogen plus progestin, which was shown to raise the risk of heart attacks as well as that of breast cancer, strokes and blood clots.

But the National Institutes of Health, sponsor of the Women's Health Initiative, decided to halt the estrogen study in March 2004, more than a year and a half early, because of a higher risk of stroke in estrogen users. In June 2004, a study of women 65 to 79 in the estrogen trial reported that the hormone could increase older women's risk of dementia.

So-called observational studies have found that postmenopausal women who choose to take estrogen were 30% to 50% less likely to have a heart attack or die of coronary heart disease. But other research showed that postmenopausal women who opted for estrogen tended to be better educated and healthier than those who didn't. Those traits, not the estrogen itself, deserved credit for the reduced risk of coronary artery disease, scientists said.

Relief of Menopausal Symptoms

The Women's Health Initiative randomly assigned 10,739 women ages 50 to 79 to either Premarin, the top-selling estrogen brand, or a placebo. Originally, participants were to have taken their pills for 8 1/2 years.

Two much smaller US trials are examining whether estrogen might protect postmenopausal women in their 50s against coronary heart disease. Former National Institute on Aging scientist Mitchell Harmon leads one of the studies. Harmon acknowledged at a news conference Monday that "we certainly have some excellent ways of preventing heart disease ... probably more effective than estrogen."

Harmon's collaborator JoAnn Manson, a Harvard women's health professor and co-author on the Hsia paper, said the new finding should be reassuring to women who are concerned about the safety of taking estrogen for relief of menopausal symptoms, the only use recommended by most medical authorities.