Women's Health Initiative

The Women's Health Initiative (WHI) was initiated by the U.S. National Institutes of Health (NIH) in 1991. The Women's Health Initiative, which consisted of three clinical trials (CT) and an observational study (OS), was conducted to address major health issues causing morbidity and mortality in postmenopausal women. In particular, randomized controlled trials were designed and funded that addressed cardiovascular disease, cancer, and osteoporosis. In its entirety, the WHI enrolled more than 160,000 postmenopausal women aged 50–79 years (at time of study enrollment) over 15 years, making it one of the largest U.S. prevention studies of its kind, with a budget of $625 million. A 2014 analysis calculated a net economic return on investment of $37.1 billion for the estrogen-plus-progestin arm of the study's hormone trial alone, providing a strong case for the continued use of this variety of large, publicly funded population study.

In the 1980s, it had become apparent that past biomedical research had focused disproportionately on white men, often neglecting prevention and treatment studies of diseases that are either unique to or more common in women and minorities. In 1985, the Public Health Service Task Force on Women's Health Issues issued recommendations that biomedical and behavioral research should be expanded to provide for the inclusion diseases and conditions identified among women of all age groups. In 1986, the NIH issued recommendations that women be included in all research studies. To further promote the study of women, in 1990, the NIH created the Office of Research on Women's Health.

In 1990, however, a report was published by the General Accounting Office (GAO), at the request of the Congressional Caucus on Women's Issues, which stated that this NIH policy was not being adequately applied to research grant applications. As a consequence, beginning in 1991, NIH strengthened the policy to require, rather than recommend, the inclusion of women in clinical research (when appropriate) in order to obtain funding.

It was these changes in societal attitudes and policy toward women's health research, in addition to the demonstration that such a large study was not only feasible, but could be done economically, that gave rise to the WHI.

Among postmenopausal women, cardiovascular disease, cancer, and osteoporosis are the leading causes of morbidity and mortality, as well as impaired quality of life. Among women in all age groups, cancer and cardiovascular disease are the leading causes of mortality. As the incidence of these diseases increases according to age, women over the age of 50 bear much of the disease burden.

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