The B-complex vitamins are active in providing the body with energy, basically by converting carbohydrates into glucose, which the body "burns" to produce energy. They are vital in the metabolism of fats and protein. In addition, the B vitamins are necessary for the normal functioning of the nervous system and may be the single most important factor in the health of the nerves. They are essential for the maintenance of muscle tone in the gastrointestinal tract and for the health of skin, hair eyes, mouth and liver. Because of the water-solubility of the B-complex vitamins, any excess is excreted and not stored. Therefore they must be continually replaced. The most important thing to remember is that all the B vitamins should be taken together. They are so inter-related in function that large doses of any one of them may be therapeutically valueless or may cause a deficiency of others. The need for B-complex vitamins increases during infection or stress. Alcoholics and individuals who consume excessive amounts of carbohydrates require a higher intake of B vitamins for proper metabolism. Coffee also uses up the B vitamins. Children and pregnant women need extra B vitamins for normal growth.