Vitamins are essential nutrients, and 'vita' is Latin for 'life'. Vitamins should be a natural part of everyone's diet and are only needed in small amounts. A vitamin can't be a metal or a mineral; it has to be an organic substance. A vitamin can't be a carbohydrate, fat, or protein either. There are 13 vitamins, four of which are fat-soluble: vitamin A, vitamin D, vitamin E, and vitamin K. The other nine vitamins are water-soluble: vitamin C and eight different types of vitamin B. Lack of vitamins leads to specific diseases.