NOW Foods Vitamin D-3 1000 IU provides a maintenance-level dose of cholecalciferol — the bioidentical form of vitamin D that is synthesized in the skin by ultraviolet B sunlight exposure. Vitamin D-3 is far superior to D-2 (ergocalciferol) for raising and maintaining blood 25(OH)D levels. At 1,000 IU this is an appropriate daily dose for adults who receive some sun exposure or who already have adequate D levels and want to maintain them. Research shows vitamin D is essential for calcium absorption and bone density, immune system regulation, mood support, cardiovascular health, and normal cell growth. NOW Foods delivers D-3 in an oil-based softgel for optimal absorption of this fat-soluble vitamin, manufactured in their GMP-certified facility with potency verification on every batch. A simple, affordable daily vitamin D supplement.