The clinical trial component consists of three subtrials: the hormone replacement trial, the dietary modification trial, and the calcium /vitamin D supplementation trial. Approximately 27,500 women aged 50 to 79 are participating in the HRT, which tests whether long-term HRT reduces coronary heart disease and fractures without increasing breast cancer risk. Women with a uterus were randomized to receive either estrogen plus progestin or a placebo. Progestin was added to protect women with a uterus from endometrial cancer. Women who have had a hysterectomy were randomized to receive either estrogen alone or a placebo. The estrogen plus progestin trial was stopped early on July 8, 2002 after an average follow-up of 5.2 years on the recommendation of the Data and Safety Monitoring Board. The estrogen alone study continued unchanged until March 2, 2004 when the NIH instructed participants to stop taking their study pills and to begin the follow-up phase of the study. . Participants in the estrogen alone study will be followed for eight to 12 years and have clinic visits every six months to assure safety and assess their health.