This study will last 6 months. Baseline measurements will take place from Weeks 1 through 4. During this time, participants will first receive a placebo over a 2-week period. Participants will then undergo a calcium balance study, involving consumption of certain study foods for 12 days and an overnight stay at the research unit for a calcium absorption test. The calcium balance study will be followed by blood collection. At Week 5, participants will be randomly assigned to receive either potassium citrate or placebo daily. For the first 9 weeks of treatment, there will be weekly blood collection and periodic urine collection for all participants. At Month 6, blood and urine will again be collected, and participants will complete questionnaires on diet and physical activity, and a second calcium balance study.