Vitamin D for Prostate Endocrine Therapy

Inclusion Criteria: * Be diagnosed with Stage I-IV prostate cancer without metastases to bone (lymph node involvement and prior diagnosis of a primary cancer is allowed) * Be age 50 years or older * Be starting ADT or have received their first ADT treatment in the past 6 months, with a total of at least 6 planned months of treatment (both luteinizing hormone-releasing hormone \[LHRH\] antagonists and LHRH agonists are permitted) * Have a total serum vitamin D between 10 and 32 ng/ml * Have a total serum calcium of less than or equal to 10.5 mg/dl * Have a normal GFR (glomerular filtration rate \> 30ml) * Agree not to take calcium and/or vitamin D supplements for the duration of the intervention other than those provided by the study * Be able to provide written informed consent * Be able to swallow pills and capsules * Be able to speak and read English Exclusion Criteria: * Have long term (greater than 3 months) use of any pharmacologic bone-modifying agent including but not limited to oral or intravenous (IV) bisphosphonates, denosumab, or teriparatide prior to enrollment * Have a diagnosis of stage IV chronic kidney disease * Have a diagnosis of grade II or greater hypercalcemia (serum calcium greater than 11.5 mg/dl) * Have a history of hypercalcemia or vitamin D toxicity/sensitivity