The Women's Health Initiative Study (WHI-OS)

Objectives:

Examine the relationship between lifestyle, socioeconomic, health, and other risk factors with cardiovascular, breast cancer, colorectal cancer and osteoporotic fracture outcomes. Secondary objectives include providing more reliable estimates of the extent to which known risk factors predict disease, more precise estimates of new occurrences of disease, and to provide a future resource for the identification of new or novel risk factors especially factors found in blood.

Background:

The Women's Health Initiative (WHI) is a long-term national health study focusing on strategies for the prevention of cardiovascular, breast and colorectal cancer and osteoporosis in postmenopausal women. The WHI study is composed of a randomized clinical trial, community prevention component, and an observational study. The randomized controlled clinical trial has three components and eligible women may elect to participate in one, two or all three of the components. The trial components include Hormone Replacement Therapy, Dietary Modification, and Calcium/Vitamin D. More than 68,000 women have been enrolled into the clinical trial component. The Community Prevention Component is a collaboration between the Centers for Disease Control and the National Institutes of Health. The purpose of the Community Prevention Component is to conduct and evaluate health programs that encourage healthy behaviors.

Subjects:

Participants in the observational study were women aged 50-79 who were ineligible or unwilling to participate in the clinical trial component or were recruited through a direct invitation for screening into the observational study. A total of 93,676 subjects were enrolled in the observational study. White women comprised 83% of the cohort (78,013), while 8% were Black (7,639) and 4% Hispanic (2,623). The remaining 5% of the cohort is comprised of Asian/Pacific Islander, American Indian, and subjects of unknown race/ethnicity. Many potential participants to the clinical trial component of the study were already undertaking a low fat diet or were using hormone replacement therapy and therefore were excluded or declined to participate in the clinical trial component. These participants were then enrolled into the observational study. Previous research has demonstrated that at the time of WHI enrollment, women undertaking hormone replacement therapy and/or low fat diets generally had healthier lifestyles than those not possessing these behaviors. The effect of the selection process was that women enrolled in the observational study tended to have healthier lifestyles compared to those enrolled in the clinical trial.

Design:

Enrollment in the observational study was conducted at 40 centers throughout the US and began in September 1993. Recruitment ended on December 31, 1998. Participants attended a baseline examination and were re-examined three years later. Participants completed annual updates of exposures and clinical outcomes. The followup interval is expected to be an average of approximately seven years.