Inclusion Criteria:

• This study will be conducted in subjects with body mass index < 38 kg/m2.
• Women must be at least 6 months since last menses.
• Subjects must be willing to maintain their usual exercise level and agree not to attempt to gain or lose weight or change their diets substantially during the study.
• Subjects will not be allowed to take their own calcium or vitamin D supplements from one week before their screening visit through the end of the study.
• They must also agree not to ingest bicarbonate- or potassium-rich products such as selected antacids and salt substitutes during the study.
• They must also agree not to consume alcohol during the study.

Exclusion Criteria:

Medications

• Oral glucocorticoid use for > 10 days in the last 3 months
• Estrogen, raloxifene, or calcitonin use in the last 6 months, bisphosphonate or teriparatide use in the last 2 years
• Current use of diuretics
• Regular use of NSAIDS (> 3 times per wk) or anabolic drugs (steroids or other). Note that subjects may use acetominophen for joint or other discomforts during the study.

Conditions/Diseases

• Renal disease including kidney stones in the past 5 years or creatinine clearance < 50 ml/min/1.73 X m2 of body surface area
• Cirrhosis
• GERD requiring treatment with alkali-containing antacids (use of Lowsium okay)
• Hyperparathyroidism
• Untreated thyroid disease
• Significant immune disorder such as rheumatoid arthritis, SLE
• Current unstable heart disease
• Active malignancy or cancer therapy in the last year
• 24-hr urine calcium > 300 mg/d after 1 wk off of calcium supplements
• Subjects with arrythmias (surgically treated arrythmias acceptable), or myocardial infarction in last 12 months
• Total hip T score of < -3.0
• Abnormal serum calcium; alkaline phosphatase >10% above the upper end of the reference range
• Adrenal insufficiency, primary aldosteronism, Bartter's syndrome
• Diabetes mellitus (fasting blood sugar > 130)
• Alcohol use exceeding 2 drinks/day
• Peptic ulcers or esophageal stricture
• Screening serum 25(OH)D levels below 16 ng/ml
• Vegetarians
• Other abnormalities in screening labs, at discretion of the study physician (principal investigator)