Vitamin D is the common name that refers to several forms of the fat-soluble vitamin. Two forms of vitamin D are important to humans: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D2 is made by plants, whereas vitamin D3 is made by the human body when the skin is exposed to ultraviolet B (UVB) rays from the sun. As little as 10 minutes of sun exposure is thought to produce enough vitamin D to prevent a deficiency.* Vitamin D aids in the absorption of calcium and phosphorous, which ensures sufficient blood levels of these minerals for proper calcification of bones and cartilaginous tissues. Sufficient vitamin D supports bone strength by increasing bone mineral density, and thereby decreases the risk of bone fractures. Maintaining vitamin D levels is crucial for preventing deficiency symptoms, which can cause skeletal deformities in children and muscular weakness and weak bones in adults.* Note: While many people are Vitamin D deficient, some are not. Please talk to your health care professional before taking this product, ask for a Vitamin D test. Vitamin D can be toxic if taken in high amounts. Human toxicity probably begins to occur after chronic daily consumption of approximately 40,000 IU/day.* *These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.