Women's Health Initiative

The Women's Health Initiative (WHI) was initiated by the National Institutes of Health (NIH) in 1991. The objective of this women's health research initiative was to conduct medical research into some of the major health problems of older women. In particular, clinical trials were designed and funded that address cardiovascular disease, cancer, and osteoporosis.

The WHI Postmenopausal Hormone Therapy Trials were part of the effort to address the high risk of cardiovascular disease in older women. By the early 1990s, many physicians had come to interpret results from previous clinical trials and studies using experimental animals as indicating that administration of an estrogen supplement to postmenopausal women would lower the incidence of cardiovascular disease. Two hormone clinical trials were designed and conducted:

The estrogen-plus-progestin study. Postmenopausal women with a uterus who are given an estrogen supplement are put at high risk for developing endometrial cancer. That risk can be eliminated by co-administration of a progestogen. The progestogen used in this WHI study was the synthetic progestin medroxyprogesterone acetate (MPA).
The estrogen-alone study. This study was specifically for women without a uterus who did not need co-administration of a progestogen.

The estrogen that was administered in the WHI studies was conjugated equine estrogen (CEE). This consistes of a mixture of estrogens isolated from horse urine (Premarin). The CEE was administered orally. Both studies were randomized, placebo-controlled studies. Half the women were given an inactive placebo rather than hormone(s). Both studies were terminated early because a reduction in cardiovascular disease was not observed for most women and some women had dangerous side-effects. In particular, an increased risk of dangerous blood clotting is associated with oral administration of CEE. In addition, co-administration of MPA with CEE was associated with an increased risk of breast cancer. Some benefits of using an estrogen supplement such as reduced risk of bone fractures were confirmed by these studies. However, for the older postmenopausal women who were recruited for this study, the undesirable side-effects of treatment generally were greater than the health benefits. Based on the results of these studies, CEE and MPA are no longer given to women in order to try to prevent cardiovascular disease in older women. Younger postmenopausal women seeking relief from conditions such as hot flashes, sleep disturbance and urinary/vaginal atrophy are still candidates for hormone replacement therapy. Alternatives to orally administered CEE and MPA are being increasingly used by women since the termination of the WHI studies. For example, other forms of estrogen (such as esterified estrogens) or topical administration of estradiol may reduce the risk of blood clotting compared to that for oral CEE.

References

J. E. Rossouw et al "Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results From the Women's Health Initiative randomized controlled trial" in Journal of the American Medical Association (2002) Volume 288, pages 321-333.
G. L. Anderson et al "Effects of conjugated equine estrogen in postmenopausal women with hysterectomy: the Women's Health Initiative randomized controlled trial" in Journal of the American Medical Association (2004) Volume 291, pages 1701-1712.
C. Straczec, et al "Prothrombotic mutations, hormone therapy, and venous thromboembolism among postmenopausal women: impact of the route of estrogen administration" in Circulation (2005) Volume 112, pages 3495-500.

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