Vitamin B3, also called niacin, is one of the eight B-complex water-soluble vitamins. Niacin has a wide range of uses in the body, helping functions in the digestive system, skin and nervous system. Niacin, a name coined from nicotinic acid vitamin, comes in several forms, including niacinamide (nicotinamide) and inositol hexanicotinate. Each of these forms has various uses as well. Food sources of niacin include yeast, meat, fish, milk, eggs, nuts, green vegetables, beans, and enriched bread and cereals. The human body can also make niacin from the amino acid tryptophan, according to the National Institutes of Health(NIH).