Niacin : Vitamin B3

Niacin (vitamin B3) is the common name for nicotinic acid, and is sometimes applied to nicotinamide (niacinamide) as well. It is a water-soluble vitamin, and its derivatves such as NADH[?] play essential roles in energy metabolism in the the living cell. Severe lack of niacin causes the deficiency disease pellagra[?], while a mild deficiency slows down the metabolism, which in turn decreases cold tolerance and is a potential contributing factor towards obesity.

Nicotinic acid reacts with hemoglobin and myoglobin in meat to form a brightly coloured complex, and thus has been used as a food additive, typically to improve the colour of minced (ground) meat. However, sometimes excess niacin is added to the meat during processing. Though still licensed as a food colouring agent in some countries, it isn't licensed as such in Europe.

Because niacin in large quantities is a vasodilator, large doses of niacin (either from vitamin B3 tablets or from treated meats) may cause harmless and short-lived but unpleasant symptoms such as extreme skin flushing resembling a sunburn, itching, gastric disturbances, and lowering of blood pressure. The amide form (strictly speaking a provitamin[?]) doesn't cause these side effects, but is also not as easily assimilated by the body.

Large doses of niacin are sometimes prescribed to combat high blood pressure.