Immunological Effects of Vitamin D Replacement Among Black/African American Prostate Cancer Patients

This trial is testing whether vitamin D supplementation can improve immune function in Black and African American men with prostate cancer who have low vitamin D levels — a common finding in this population that may be linked to worse health outcomes. **You may be eligible if...** - You are an African American male, 18 or older - You have a history of localized, locally recurrent, or metastatic prostate cancer - Your vitamin D level is below 30 ng/mL **You may NOT be eligible if...** - You have a known allergy to vitamin D - You have end-stage kidney failure on dialysis - You have liver cirrhosis - You are already taking more than 400 IU/day of vitamin D - You have a history of high calcium levels (hypercalcemia) - You have had chemotherapy, surgery, or radiation within the past 3 weeks Talk to your doctor to see if this trial is right for you.