A large, multi-center heart disease prevention study, part of the Women's Health Initiative (WHI), found that estrogen-alone hormone therapy had no effect on coronary heart disease risk but increased the risk of stroke for postmenopausal women. The study also found that estrogen-alone therapy significantly increased the risk of deep vein thrombosis, had no significant effect on the risk of breast or colorectal cancer, and reduced the risk of hip and other fractures.

The WHI is sponsored by the National Heart, Lung, and Blood Institute (NHLBI), part of the National Institutes of Health (NIH).

The estrogen-alone study was stopped at the end of February 2004 because the hormone increased the risk of stroke and did not reduce the risk of coronary heart disease, a key question of the trial. The study was to have ended in March 2005. Initial findings appear in the April 14 issue of "The Journal of the American Medical Association".

A separate report on the WHI Memory Study of estrogen alone's effects on dementia and cognitive function will be published soon.

"These findings confirm that estrogen-alone therapy should not be used to prevent chronic disease," said NHLBI acting director Dr. Barbara Alving. "We believe the findings support current FDA recommendations that hormone therapy only be used to treat menopausal symptoms and that it be used at the smallest effective dose for the shortest possible time."

"The results make clear that hormone therapy does not protect women against coronary heart disease and increases their risk for stroke," said Dr. Jacques Rossouw, WHI project officer at NHLBI. "This may be especially true for older women, such as those aged 60 and older in this study."

As of July 2003, about 10 million American women were taking some form of hormone therapy. It is estimated that about 6.7 million of those take estrogen alone and 3.3 million take estrogen plus progestin. The drugs tested in the WHI are those most commonly used in the United States.

The estrogen-alone study involved 40 clinical centers and 10,739 generally healthy postmenopausal women ages 50-79 who did not have a uterus. Their average age at enrollment was nearly 64 and about 70 when the study stopped. They enrolled in the study between 1993 and 1998.

About 75 per cent of the women were white, 15 per cent black, and 6 per cent Hispanic. Most of the women were overweight and about 8 per cent had diabetes. About 35 per cent of the women had used hormone therapy in the past and about 13 per cent were current users at the time they enrolled in the study.

The women were randomized to two groups-one received 0.625 mg/day of conjugated equine estrogens (Premarin) and the other a placebo. Premarin and the placebo were supplied by Wyeth-Ayerst Research.

The women were followed for an average of 6.8 years. They visited their clinic at least once a year, and had annual mammograms and clinical breast exams.

The study was carefully monitored by an independent Data and Safety Monitoring Board (DSMB). The NIH made the decision at the beginning of February 2004 to stop the study drugs. The "JAMA" article includes data collected through February 2004.