focuses on identifying potential problems and finding strategies for dealing with them, in order to increase the probability that the WHI will make a meaningful contribution to the health of women in the United States.


The WHI is the largest research study ever funded by NIH. Budgeted at $625 million over 14 years, it is designed to test strategies to prevent cardiovascular disease, breast cancer, and osteoporotic fractures—leading causes of death, disability, and decreased quality of life for older women.

The WHI consists of three major components: the Clinical Trial, the Observational Study, and the Community Prevention Study. By far the costliest and most complex of these components is the Clinical Trial (CT), which will involve 63,000 postmenopausal women at 45 clinical centers across the United States. The CT has three branches that, as currently designed, will test several hypotheses:

  • Dietary Modification (DM)

    Primary hypotheses:

    A low fat dietary pattern reduces the risk of breast cancer and colorectal cancer.

    Secondary hypothesis:

    A low fat dietary pattern reduces the risk of coronary heart disease.

  • Hormone Replacement Therapy (HRT)

    Primary hypothesis:

    Estrogen replacement therapy (ERT) and progestin and estrogen replacement therapy (PERT) reduce the risk of cardiovascular disease.

    Secondary hypotheses:

    ERT and PERT reduce the risk of osteoporotic fractures.

    ERT and PERT increase the risk of breast cancer.

  • Calcium and Vitamin D Supplementation (CaD)

    Primary hypothesis:

    Supplementation reduces the risk of hip fractures.

    Secondary hypotheses:

    Supplementation reduces the risk of other fractures.

    Supplementation reduces the risk of colorectal cancer.

The Observational Study will interview, obtain blood specimen samples from, and follow another 100,000 women who were ineligible or unwilling to participate in the CT, generating a rich database on the CT hypotheses and related health questions. Committee calculations corroborated by estimates provided by the Clinical Coordinating Center, find the CT and the

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