The studies will be performed in the outpatient facility of the University of Chicago GCRC. Every 3 months for the first 6 months and every 6 months for the reminder of 2 years, the subjects will come in the morning in the fasting state, provide a urine sample (second morning void) and blood sample for measurement of biochemical markers of bone turnover. Height and weight will be recorded at each visit, and any change in health status, including fractures ascertained. We will also assess other factors known to influence bone turnover, such as diet and physical activity. Every 12 months, the subjects will fill out Block food frequency questionnaire from Berkley Nutrition Services [29]. In addition, every 6 months they will fill out a calcium intake questionnaire (included in Appendix), which will be analyzed by the CRC nutritionist and a short physical activity questionnaire, which was used in PEPI trial [30] for assessment of physical activity. Medication compliance will be assessed by questioning the patients and counting the number of calcium and alendronate tablets remaining from the previous visit.