This randomized clinical trial will enroll 136 men recently diagnosed with Early-Stage prostate cancer. Men must be 19 or older with a prostate biopsy Gleason score ? 6 and PSA ?10 who have decided that active surveillance is their present treatment option. Study visits will be every 4 months for just over a year in Charleston, S.C. There will be two groups, one taking vitamin D3 supplement and the other taking a placebo. Assigment to each group will be by chance and neither the particpant nor the study team will know to which group they are assigned. Blood and urine samples will be collected at each visit for research purposes. A survey relating to the subjects' decision making about their biopsies will be completed at the baseline and final visits. Waist/hip ratio and blood pressure measurements will also be obtained at the baseline and final study visits. Each participant will be in the study until a repeat prostate biopsy is performed by their own Urologist as Standard of Care for Active Surveillance regimen.