Vitamin D is involved in many bodily functions and plays a vital role in immune health and maintaining healthy bones and teeth. Vitamin D is produced when you expose your skin to sunlight and it is found in some foods, such as fatty fish and fortified dairy products. Learn how to spot vitamin D deficiency symptoms, what foods are high in vitamin D, how much to take daily, and whether D2 or D3 is best for you. Vitamin D (also referred to as calciferol) is a fat-soluble vitamin that is naturally present in a few foods, added to others, and available as a dietary supplement. It is also produced endogenously when ultraviolet (UV) rays from sunlight strike the skin and trigger vitamin D synthesis. Vitamin D is an essential micronutrient that helps your body absorb calcium, protects the health of your bones and teeth, reduces inflammation, regulates blood sugar, and boosts your immune response. Vitamin D is a nutrient the body needs, along with calcium, to build bones and keep them healthy. The body can absorb calcium only if it has enough vitamin D. Calcium is a major part of bones. Vitamin D also has many other uses in the body. It supports immune health and helps keep muscles and brain cells working. Vitamin D helps maintain strong bones. Learn how much you need, good sources, deficiency symptoms, and health effects here. Unlike the other twelve vitamins, vitamin D is only conditionally essential in the diet, as with adequate skin exposure to the ultraviolet B (UVB) radiation component of sunlight there is synthesis of cholecalciferol in the deeper layers of the skin's epidermis. Learn more about Vitamin D uses, effectiveness, possible side effects, interactions, dosage, user ratings and products that contain Vitamin D. More specifically, you need vitamin D so your body can use calcium and phosphorus to build bones and support healthy tissues. With chronic and/or severe vitamin D deficiency, a decline in calcium and phosphorus absorption by your intestines leads to hypocalcemia (low calcium levels in your blood). Vitamin D helps regulate the amount of calcium and phosphate in the body. These nutrients are needed to keep bones, teeth and muscles healthy. A lack of vitamin D can lead to bone deformities such as rickets in children, and bone pain caused by a condition called osteomalacia in adults.