Niacin (vitamin B3, nicotinic acid, nicotinamide) is a water-soluble vitamin found in dairy products, poultry, fish, lean meats, nuts, and eggs. Legumes and enriched breads and cereals also supply some niacin. Niacin assists in the functioning of the digestive system, skin, and nerves. Niacin can be formed in the body by the conversion of the amino acid tryptophan.
Niacin is also important for the conversion of food to energy. In the body niacin is a component of two coenzymes (NAD and NADP) that play important roles in cell respiration. Severe deficiencies of niacin are the principal cause of pellagra, a deficiency disease characterized by abnormalities of the skin, mouth and gums, gastrointestinal tract and central nervous system.
When used as a supplement in high doses, niacin inhibits VLDL cholesterol secretion and decreases production of LDL ("bad") cholesterol while raising HDL ("good") cholesterol levels. The dose of niacin needed to produce these beneficial effects is 500 to 2000 mg/day - much more than can be obtained from regular dietary intake. Side effects from niacin can include flushing, itching, rashes, or GI distress. Niacin should not be taken by people with gout or severe peptic acid or liver disease and should be used with caution by people with diabetes.