Does Treatment of Hypovitaminosis D Increase Calcium Absorption?

Inclusion Criteria: * women at least five years past onset of menopause, defined as date of last menses (ages reported above are the range in ages of the participants recruited to the study) * serum 25(OH)D 16-24 ng/ml by reverse phase HPLC * calcium intake \< or = 1,100 mg daily Exclusion Criteria: * Intake of \>1,100 mg of calcium per day through the combination of diet and supplements * Hypercalcemia (baseline serum calcium above the normal reference range) * Nephrolithiasis, documented in the medical record or by patient report * Inflammatory bowel disease, malabsorption, chronic diarrhea, or use of antibiotics within the past month * Creatinine \>2.0 mg/dL * Hypercalciuria (baseline urine calcium: creatinine ratio \>0.25) * Current use of medications known to interfere with vitamin D and/or calcium metabolism, including oral steroids or anticonvulsants * Ongoing or recent (past six months) use of bisphosphonates, estrogen compounds, calcitonin or teriparatide, as these compounds may independently affect retention of calcium within bone * Diagnosis of, or evidence for, osteomalacia, manifest by serum 25(OH)D \< 16 ng/ml or the presence of at least two of the following blood tests: low calcium, low phosphorus, or elevated alkaline phosphatase (23). * Prior adult clinical fragility fracture or baseline T-score below -3.0 at the lumbar spine or femur