A deficiency plays a key role in the development of type 1 diabetes. Vitamin D is needed for islet cells to produce insulin, the hormone that allows cells to take up blood sugar. Without enough Vitamin D, islet cells don't produce insulin. Helps regulate white blood cells that make up the immune system; Vitamin D with calcium has shown to reduce osteoporosis and hip fractures; improves the absorption and utilization of calcium and phosphorus; hardens and repairs bones; prevents rickets, treats hypocalcaemia, and promotes normal growth in children; supports the healthy function of the thyroid gland; may help prevent colon cancer.