Fat-Soluble Vitamins; Vitamin D
Vitamin D Vitamin D food sources Vitamin D differs from the other nutrients in that the body can synthesize it, with the help of sunlight, from a precursor that the body makes from cholesterol. Therefore, vitamin D is not an essential nutrient; given enough time in the sun, people need no vitamin D from foods. Also known as calciferol , vitamin D comes in two major forms. Vitamin D2 derives primarily from plant foods in the diet. Vitamin D3 derives from animal foods in the diet and from synthesis in the skin. These two forms of vitamin D are similar and both must be activated before they can fully function. To make vitamin D, ultraviolet rays from the sun hit a precursor in the skin and convert it to pre-vitamin D3, which is converted to vitamin D3 with the help of body's heat. To activate vitamin D _whether made in the body or consumed from the diet _two hydroxylation reactions must occur. First, the liver adds an OH group, and then the kidneys add another OH gr...