Participants will be seen monthly during the first year of the study and every two months during the second year. Entry/baseline, 12-month and 24-month visits will take place at the SLRHC Body Composition Unit. All other visits will take place at the site where usual care is received. Vitamin D3/placebo will be administered during study visits every 2 months. At monthly visits during the first year and every 2 months during the second year after randomization, a 30 or 60 day supply of calcium/placebo will be dispensed. Adherence to calcium supplementation will be assessed at each visit.