United States Women's Health Initiative Study 1991-2005

The study consisted of a set of technical trials and an observational study targeted to post-menopausal women. The clinical trials tested the effects of postmenopausal hormone therapy, diet modification, calcium and vitamin D supplements of heart disease, fractures, and breast and colorectal cancer. The observational study aimed to give reliable estimates to the extent known risk factors predicted heart disease, cancers and fractures, and to identify new risk factors. A total of 93,676 women participated on the observational study. Overall, including both the observational and clinical trials 161,808 women participated.