Niacin (Vitamin B3)

Niacin is part of the B complex (as seen from its alternative name, vitamin B3) and is found in two forms in supplements; niacin (nicotinic acid) and niacinamide (nicotinamide). The name nicotinic acid comes from the first time niacin was synthetically prepared, from nicotine; there are some similarities in chemical structure, but niacin is nothing like nicotine in biological activity.
Niacin is only conditionally a vitamin, as it can be made in the body from the amino acid tryptophan. However, there are many other uses for tryptophan, and so niacin can become deficient in the diet if the diet is low in both tryptophan and niacin. This happens if grains are eaten as a major part of the diet in forms without the husk (for example white rice) or if the major grain eaten is maize, which is naturally low in niacin, and the maize is prepared without lime. The traditional way of preparing maize involves lime, and this frees the tryptophan and makes niacin deficiency unlikely, Niacin deficiency is called pellagra, and is characterised by High sensitivity to sunlight, Aggression, Dermatitis, alopecia, oedema, Smooth beefy red sore tongue, Red skin lesions, Insomnia, Weakness, Mental confusion, Ataxia, paralysis of extremities, peripheral neuritis, Diarrhoea, and eventually dementia and death.
Niacin in the form of nicotinic acid has another specific use, unrelated to its usefulness as a vitamin. Niacin blocks breakdown of fats in fatty tissue and the production of cholesterol in the blood; hence it can be useful in reducing cholesterol, particularly LDL and VLDL, the "bad" forms of cholesterol that tend to cause deposition of plaque in the arteries.
Niacin is generally safe, but in very large amounts, and especially in people whose liver is already suspect, can cause liver damage. Niacin virtually always causes short-term (20-30 minutes) flushing of the skin, because niacin dilates surface blood vessels.