We will study the relative importance of high calcium intake and vitamin D supplementation for calcium homeostasis, as determined by serum parathyroid hormone (PTH) and biochemical bone markers. We also intend to examine the interaction of vitamin D and calcium intake on calcium homeostasis. We hypothesize that optimal calcium supplementation and optimal vitamin D supplementation will lead to lower serum levels of PTH and markers of bone resorption compared with the placebo. We also theorize that when taken together, optimal calcium supplementation and optimal vitamin D intake will result in lower serum levels of PTH and bone markers compared with calcium or vitamin D taken alone.

Inclusion Criteria:

• Healthy women aged 45 and above who have been menopausal at least 1 year (absence of menstrual period for a period of 12 months or more)

Exclusion Criteria:

• Any chronic medical illness including uncontrolled diabetes mellitus, recent history of myocardial infarction, or heart failure, malignancy, uncontrolled hypertension, obesity (BMI>35 kg/m2), history of anemia, leukemia, or other hematologic abnormalities, lupus, rheumatoid arthritis, or other rheumatologic disease, or kidney disease of any kind as determined by history and physical examination.
• Subjects with osteoporosis of the hip (total hip T-score equal or less than -2.5) or taking medications for osteoporosis such as bisphosphonates will be excluded.
• Pregnancy.
• Use of medication that influences bone metabolism (i.e. anticonvulsant medications, chronic use of steroids and high dose diuretics).
• Significant deviation from normal in medical history, physical examination, or laboratory tests as evaluated by the primary investigator.
• Patients with a history of hypercalciuria, hypercalcemia, nephrolithiasis, and active sarcoidosis will also be excluded.
• Participation in another investigational trial in the past 30 days prior to the screening evaluation.
• Unexplained weight loss of >15% during the previous year or history of anorexia nervosa.
• Medications that interfere with vitamin D metabolism.
• Patients with a habitual dietary calcium intake that exceeds 800 mg/day.
• Smokers greater than 1 pack per day will be excluded.
• Patients reporting alcohol intake greater than 2 drinks daily.
• Serum 25-hydroxyvitamin D level > 75 nmol/L.