A nationwide study to examine the effects of long-term estrogen use among predominantly healthy postmenopausal women who have had hysterectomies has found that the therapy causes an increased risk of stroke. Based on these results, the 11,000 participants in the study — a component of the Women's Health Initiative (WHI), whose clinical coordinating center is housed in the Public Health Sciences Division — have been instructed to stop taking their pills and to begin the follow-up phase of the study. The National Institutes of Health (NIH)-coordinated trial was scheduled to continue until 2005.
After careful consideration of the data, the NIH researchers concluded that with an average of nearly seven years of follow-up completed, estrogen alone does not appear to either increase or decrease heart disease, a key question of the study. At the same time, estrogen alone appears to increase the risk of stroke and decrease the risk of hip fracture. It does not appear to increase the risk of breast cancer.
The increased risk of stroke in the estrogen-alone study is similar to what was found in the WHI study of estrogen plus progestin when that trial was stopped in July 2002. In that study, women taking estrogen plus progestin had eight more strokes per year for every 10,000 women than those taking the placebo.
The NIH has determined that the results would not likely change if the estrogen trial continued to its planned completion and that enough data has been obtained to assess the overall risks and benefits of the use of estrogen in this trial. WHI researchers have begun a detailed analysis of the data from the estrogen-alone study and expect to report full results in the next two months in a peer-reviewed journal.
WHI is a 15-year, multimillion-dollar study that seeks to find ways to prevent cardiovascular disease, osteoporosis and cancer, all of which have a significant impact on women's health. More than 160,000 women nationwide, including some 3,500 in Washington, take part in the study.
Established by NIH in 1991, the WHI involves 40 clinical centers nationwide, including one in Seattle that is jointly run by the center and the University of Washington.
WHI is sponsored by the National Heart, Lung and Blood Institute, in collaboration with the National Cancer Institute, the National Institute of Arthritis and Musculoskeletal and Skin Diseases, the National Institute on Aging, and the Office of Research on Women's Health. WHI studies at the center are also supported by private donations.