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Here is a breakdown of major studies that were done on postmenopausal women who took hormone therapy (HT):
Heart and Estrogen/Progestin Replacement Study
This large randomized clinical trial examined the effect of HT on women with heart disease. The Heart and Estrogen Progestin Replacement Study (HERS) found that the use of estrogen plus progestin in postmenopausal women with heart disease did not prevent further heart attacks or death from coronary heart disease. In fact, their risk rose in the first year, and then dropped after that.
HT also had no significant effect on the overall risk of stroke in the study group. Furthermore, HT increased the risk of clots in the veins and lungs. The trial revealed that estrogens might actually increase the risk for gallstones. The effects of hormone therapy depend on the presence of menopausal symptoms; women without flushing had greater declines in physical measures, while women with flushing had improvements in emotional measures of quality of life.
HERS involved 2,763 postmenopausal women, average age 67, who were treated for about four years. Women were randomly assigned to an estrogen and progestin combination or placebo. The study was funded by Wyeth-Ayerst Laboratories and supported by the National Heart, Lung and Blood Institute (NHLBI) of the National Institutes of Health (NIH).
Women's Health Initiative
In 1991 the NIH launched the Women's Health Initiative (WHI), one of the largest studies of its kind ever undertaken in the United States. The WHI is a 15-year research project of women's health concerns after menopause. The HT component of the WHI examined whether estrogen or an estrogen and progestin combination can help prevent heart disease, breast cancer, colorectal cancer and osteoporosis.
The estrogen plus progestin study was stopped in July 2002 when results showed a small increase in the number of heart attacks, strokes and blood clots in women receiving hormone therapy. Another arm of the study looking at estrogen alone on women who had hysterectomy was stopped in April 2004 because there was an increased risk for stroke. The guidelines for HT changed as a result of the WHI studies, which advised against using HT to prevent chronic disease in post-menopausal women and advises only short-term use of HT at the lowest effective dose for treating menopausal symptoms.
In 2007 the WHI reported that women who begin HT within 10 years of menopause may have less of a risk for coronary heart disease due to HT than women who are farther away from menopause. The farther a woman was from the start of menopause when she began using HT, the greater her risk of heart disease due to HT use.
Women's Estrogen for Stroke Trial
This clinical trial examined estrogen therapy among postmenopausal women with a history of stroke. Results suggest that ERT was not effective for preventing another stroke or death. Women who took estrogen had a higher risk of fatal stroke or more severe impairments after stroke than women who took placebo. The researchers studied 664 postmenopausal women with an average age of 71 years who had experienced an ischemic stroke or a trans ischemic attack (TIA) within the previous 90 days. Ischemic strokes and TIAs result from blockages in the vessels that supply blood to the brain. The study was funded by the National Institute of Neurological Disorders and Stroke (NINDS).
Postmenopausal Estrogen/Progestin Interventions Trial
The NHLBI and other units of the NIH started this major clinical trial in 1987. This study assessed differences between placebo, unopposed estrogen and estrogen/progestin regimens on selected heart disease risk factors in 875 healthy postmenopausal women over a three-year period.
Postmenopausal Estrogen/Progestin Interventions (PEPI) Trial found that each of the active hormone therapies improved key heart disease risk factors - improving cholesterol levels and lowering fibrinogen levels. Fibrinogen allows blood to clot more readily, increasing the risk of heart disease and stroke.
PEPI also examined HT's effects on bone mass and found that HT not only slows the bone loss that occurs with menopause, but also significantly increases bone mass. These effects on bone were strongest among older women and those who had not recently used hormones. All of the hormone regimens increased bone density. Smokers, who generally lose bone mass more quickly than nonsmokers, gained as much bone mass on average as nonsmokers. However, HT does not reduce fractures.
The NHLBI is supporting several other trials:
- Estrogen Replacement and Atherosclerosis (ERA) Trial - an angiographic study comparing estrogen, estrogen plus progestin, and placebo in 309 postmenopausal women with coronary heart disease. The key finding of this study was that postmenopausal hormone therapy does not slow the progression of heart disease.
A separate, completed study, the Estrogen in the Prevention of Atherosclerosis Trial, or EPAT, found that unopposed estrogen replacement therapy appears to reverse atherosclerosis in postmenopausal women who are not receiving cholesterol-lowering therapy. The study, conducted by the University of Southern California Atherosclerosis Research Unit, looked at the progression of atherosclerosis over two years in 222 healthy, postmenopausal women who either took unopposed estrogen or a placebo.
This article was reviewed and updated June 2007.
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