PROPOSAL (Adapted from the applicant's abstract): The candidate is Assistant Professor of Medicine at the UTSM, Memphis. UTSM has a Clinical Research Center that provides resources through which the candidate can perform patient-oriented clinical research. The Departments of Internal and Preventive Medicine have numerous ongoing experimental and observational trials. This provides opportunities for the candidate to collaborate with faculty. The candidate has proposed a five-year training plan, with the long- term goal of practicing medicine, performing patient-oriented research and teaching residents and students. The candidate also plans to serve as a resource and mentor for faculty who wish to learn research design and literature interpretation. The candidate will complete a Master's degree in epidemiology and take advanced courses beyond the degree. She will attend research meetings in the Metabolic Bone Center, the Department of Preventive Medicine, and the St. Jude-LeBonheur-UTSM Bone Coalition. Finally, the candidate will investigate the effect of magnesium (Mg) on bone loss in healthy older adults. Mg supplementation has attractive but unproven benefits in bone health. In uncontrolled and unblinded trials, Mg supplementation leads to large gains in bone density. The mechanism of action is not known. Severe Mg deficiency has an impact on calciotropic hormones, and changes in these hormones may have a direct effect on bone as well as an effect on gut calcium absorption. Whether Mg supplementation affects calciotropic hormones in healthy subjects without severe Mg deficiency is not known. Mild Mg deficiency may be common, since as many as 75% of the elderly do not meet the estimated average requirement for Mg. This study will test the following hypotheses: 1) Mg supplementation reduces bone resorption in healthy adults; 2) Mg supplementation increases gut calcium absorption; and 3) The increase in calcium absorption occurs through changes in circulating levels of calciotropic hormones. This will be a double-blinded placebo-controlled trial of Mg (500 mg/day) in 92 healthy men and women between the ages of 55-75.