Vitamin D deficiency is highly prevalent in older people in the absence of vitamin D supplementation. The limited data available show marked inter-individual variability in response to vitamin D supplementation in very old, frail elderly with almost 25% remaining vitamin D deficient (25-OH D < 20 ng/mL) when receiving the currently recommended 800 IU/day vitamin D. This proposal is for exploratory research on the use of a wide range of oral vitamin D3 doses in frail elderly living in controlled living environments.

The investigators will determine the dose response relationship of circulating total and unbound 25-OH vitamin D3 to supplemental vitamin D3 at daily doses of 800 (currently recommended for the elderly), 2000, and 4000 IU or 50,000 IU/weekly in a randomized blinded investigation of 16 weeks duration. The investigators will also compare the efficacy of each dosing regimen in achieving 25-OH vitamin D levels >20 ng/mL (50 nmol/L) and identify covariates that contribute to inter-individual variation in the dose response relationship. In patients with osteoporosis, relationships between unbound vs. total 25-OH on intact parathyroid hormone and a marker of bone resorption (beta-Ctx) will be analyzed. The investigators will also examine responses of inflammatory cytokines.

Note: as of April 8,2014, there will be no further enrollment in the 50,000 IU/weekly dose group

Inclusion Criteria:

• age over 65
• medically stable
• residing in long-term care or assisted living

Exclusion Criteria:

• hypercalcemia or high risk for hypercalcemia
• active cancer or malignancy other than non-melanoma skin cancer
• severe renal disease (eGFR <30 ml/mkin/M2)
• small bowel resection or intestinal bypass surgery
• hyperparathyroidism
• granulomatous disease
• clinically unstable (changes in medications or diagnoses within a month, hospitalizations, within 6 months)
• allergy to vitamin D

Elderly (>65 yr) clinically stable long-term stay nursing home residents with no contraindications or allergy to D, osteoporosis or a history of fractures and receiving over 800 IU/day D, treatment for severe D deficiency or investigational agent in the prior six months on no D or had stable D doses for over two months .

16 weeks