What does vitamin D do? Your body needs vitamin D to absorb calcium, which keeps your bones, teeth and muscles healthy. In the UK, around 1 in 6 adults have low levels of vitamin D in their blood, which means they’re at greater risk of developing a deficiency. 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 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. 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. 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. Find out about vitamin D, including what it does, how much you need, and how to ensure you get enough. 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).