21st Century High Potency Vitamin D3-1IU Tablets For Bone & Immune Health Are formulated with Vitamin D3 (Cholecalciferol), the bodys preferred form of vitamin D commonly known as the Sunshine Vitamin, which is obtained from diet or produced by the skin through sunlight exposure and becomes increasingly important as sun exposure is avoided and absorption decreases with age, as vitamin D promotes calcium absorption in the gut, maintains adequate serum calcium and phosphate levels to enable normal bone mineralization and prevent deficiency-related bone conditions, supports bone growth and remodeling by osteoblasts and osteoclasts, helps regulate calcium and phosphorus absorption, facilitates normal immune system function, supports normal growth and development of bones and teeth, and helps maintain the health of bones, teeth, immune system, brain, and nervous system.