Vitamin D is a fat-soluble vitamin that we make when our skin is exposed to sunlightVitamin D is a fat-soluble vitamin that we make when our skin is exposed to sunlight. The most common sources are egg yolks, oily fish, vitamin D enhanced mushrooms and some fortified foods. A deficiency in vitamin D causes rickets, and thin, brittle bones — Jane McClenaghanWe need vitamin D for a whole range of functions in the body. Foods rich in natural Vitamin D (Alamy Stock Photo)Vitamin D promotes calcium absorption and is essential for bone density. Along with calcium and other mineral, vitamin D is an important nutrient to help protect against osteoporosis and osteopenia.