Vitamin D promotes intestinal calcium and phosphorous absorption and reduces urinary calcium loss, essential mechanisms for maintaining proper calcium levels in the body and for healthy bone composition. A positive role for vitamin D in supporting colon health has been suggested. Overall, vitamin D is believed to provide general cellular support potential, including for breast and prostate tissue. While 800 iu of vitamin D-3 is the RDA, given the low levels of vitamin D in the U.S. population, this capsule size reflects the increased tendency for a more therapeutic approach to vitamin D-3 supplementation.