Vitamin D3 Supplementation in Participants Diagnosed With Early-Stage Prostate Cancer Who Decide to Undergo Active Surveillance Treatment Regimen.

Inclusion Criteria: * lowgrade prostate cancer * serum PSA less than/equal to 10 ng/ml * Gleason score less than/equal to 6 * referred from their treating physician with treatment plan of active surveillance for one year * serum creatinine less than/equal to 2.0 mg/dL * serum phosphate (measured as phosphorus)greater than 2.3 and less than 4.8 mg/dL * serum calcium greater than 8.5 and less than 10.5 mg/dL Exclusion Criteria: * concurrent malignancy, except non-melanoma skin cancer * history of sarcoidosis * history of high dose (greater than 1,000 IU daily) vitamin D3 supplementation * history of hypercalcemia * treatment with lithium medication