Vitamin D-3 - Now Foods Vitamin D-3 - Vitamin D-3 plays such a large role in the body considering the vitamin is converted into its own pro-hormone that flows through the bloodstream. This vitamin is essential for the absorption of calcium and phosphorus from various food sources to support bone health. D-3 vitamins have been found to prevent autism, cancer, autoimmune disease, diabetes, osteoporosis and more. Vitamin D-3 deprivation may be associated with breast cancer, colon cancer, prostate cancer in men, depression, weight gain, heart disease and other severe illnesses. A dietary supplement is recommended for individuals who have limited sun exposure throughout the year taking in account that Vitamin D stores are low in the winter and fall seasons.