Vitamin D is a fat-soluble vitamin and is found in butter, margarine, liver and egg yolks. It is used in maintaining levels of the minerals phosphorous and calcium in the blood, and a lack of the vitamin in the diet leads to rickets - a disease that causes bone deformity. Unusually for a vitamin, our diet is not the only source because it is also produced by the action of sunlight on the skin. Like the other three fat-soluble vitamins, it can be stored for moderate periods in our liver.
