Vitamins are similar to the energy nutrients in that they are organic mole cules, but differ in the fact that the body does not get energy directly from these molecules. Instead, vitamins serve as enzyme assistants, or coen zymes. Some vitamins, specifically the B-complex vitamins, are directly involved in the processing of energy nutrients, specifically lipids and carbohydrates. Certain vitamins serve as protectors of the delicate cellular machinery. These are called the antioxidants and are best represented by vitamins C and E. Others aid in the vision pathways (vitamin A), or in the building of healthy bones (vitamins D and A). Nutritionists divide the vitamins into two groups based upon how they interact with the body.
The first are the water-soluble vitamins, a group that consists of vitamin C and the B vitamins. These vitamins are readily absorbed by the digestive system and, with a few exceptions, do not require special processing. The other class, known as the fat-soluble vitamins (vitamins A, D, E, and K), are frequently treated in the same manner as the triglycerides, meaning that they are packaged into specialized lipoproteins and transported by the lymphatic system. In general, both classes are required in relatively small quantities (micrograms or less) daily by the body.