Women's Health Initiative

Lead Contacts and/or Principal Investigators (PIs):

  • Ross Prentice, Ph.D.
    Fred Hutchinson Cancer Research Center
    University of Washington
  • Jacques Rossouw, M.D.
    National Heart, Lung, and Blood Institute (NHLBI)

Funded Since: 1992
Funding Source: NHLBI
Year(s) of Enrollment: 1993-1998
Study Website: http://www.whi.orgExternal Web Site Policy

The Women's Health Initiative (WHI) is a long-term national health study that has focused on strategies for preventing heart disease, breast and colorectal cancer, and osteoporotic fractures in postmenopausal women. These chronic diseases are the major causes of death, disability, and frailty in older women of all races and socioeconomic backgrounds.

This multi-million dollar, 20-year project, sponsored by the National Institutes of Health (NIH), NHLBI, involves 161,808 women aged 50 to 79, and is one of the most definitive, far-reaching clinical trials of postmenopausal women's health ever undertaken in the United States. The WHI Clinical Trial and Observational Study focused on many of the inequities in women's health research and will continue to provide practical information to women and their physicians about hormone therapy, dietary patterns, calcium/vitamin D supplementation, and their effects on the prevention of heart disease, cancer, and osteoporotic fractures.

The WHI has two major parts: a randomized Clinical Trial (CT) and an Observational Study (OS). The randomized controlled CT enrolled 68,132 postmenopausal women between the ages of 50 and 79 into trials testing three prevention strategies. If eligible, women could choose to enroll in one, two, or all three of the trial components. The components are:

  • Hormone Therapy Trials (HT): This component examined the effects of combined hormones or estrogen alone on the prevention of coronary heart disease and osteoporotic fractures, and associated risk for breast cancer. Women participating in this component took hormone pills or a placebo (inactive pill) until the Estrogen plus Progestin and Estrogen Alone trials were stopped early in July 2002 and March 2004, respectively. All HT participants continued to be followed without intervention until close-out.
  • Dietary Modification Trial (DM): The Dietary Modification component evaluated the effect of a low-fat and high fruit, vegetable, and grain diet on the prevention of breast and colorectal cancers and coronary heart disease. Study participants followed either their usual eating pattern or a low-fat dietary pattern.
  • Calcium/Vitamin D Trial (CaD): This component began 1 to 2 years after a woman joined one or both of the other clinical trial components. It evaluated the effect of calcium and vitamin D supplementation on the prevention of osteoporotic fractures and colorectal cancer. Women in this component took calcium and vitamin D pills or a placebo.

The Observational Study (OS) is examining the relationship between lifestyle, health, and risk factors and specific disease outcomes. This component involves tracking the medical history and health habits of 93,676 women. Recruitment for the observational study was completed in 1998 and participants were initially followed for 8 to 12 years.

The Fred Hutchinson Cancer Research Center in Seattle, WA, serves as the WHI Clinical Coordinating Center for data collection, management, and analysis of the WHI. The WHI CT and OS were conducted at 40 Clinical Centers nationwide. Recruitment began in September 1993 and continued through October 1998 for the CT. The OS enrolled through December 1998. Close-out of the CT occurred between October 2004 and March 2005, at which time participants were invited to enroll in the WHI Extension Study, which involves follow-up health tracking without intervention through 2010. A further extension to 2015 is being implemented.

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