Niacin, or vitamin B3, is a water-soluble B vitamin found naturally in some foods, added to foods, and sold as a supplement. The two most common forms of niacin in food and supplements are nicotinic acid and nicotinamide. The body can also convert tryptophan—an amino acid—to nicotinamide. Niacin is water-soluble so that excess amounts the body does not need are excreted in the urine. Niacin works in the body as a coenzyme, with more than 400 enzymes dependent on it for various reactions. Niacin helps to convert nutrients into energy, create cholesterol and fats, create and repair DNA, and exert antioxidant effects. [1,2]