Niacin (nicotinic acid)-One of the B complex vitamins. Niacin functions as a component of the coenzymes, NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate). Niacin [but not nicotinamide, also called niacinamide] also functions as a vasodilator and in reducing plasma cholesterol. You may have experienced the vasodilation first hand, if you've ever taken niacin supplements on an empty stomach, shortly after, developing flushing of the skin, and a sensation of heat.
Sources of niacin
Good sources of niacin are unrefined grains, cereals, meats, liver, and milk. Niacin can also be synthesized from the amino acid tryptophan (see proteins). Niacin synthesis from tryptophan, however, is inefficient, since a large proportion of the amino acid is required for the production of but a small amount of niacin.
RDA of niacin
Daily requirements for niacin are measured in niacin equivalents (NE). The NE takes in consideration the amount of dietary tryptophan as a niacin source, since niacin can be synthesized from tryptophan. One NE is defined as 1 mg of niacin or 60 mg of tryptophan (the body uses 60 mg of tryptophan to manufacture 1 mg of niacin). The adult requires about 13 NE per 1000 kcal from the diet.
Deficiency of niacin
Deficiency of niacin results in the condition known as Pellagra (Italian, meaning "rough skin"). Pellagra is characterized by dermatitis, inflammation of mucous membranes, diarrhoea (diarrhea), and psychic disturbances. The dermatitis occurs on the portions of skin exposed to light or trauma. Mental symptoms include depression, irritability, confusion, anxiety, delusions, and hallucinations. Always remember the 3 D's: dermatitis, diarrhoea, and dementia (and the fourth D, if untreated: death).
Toxicity of niacin
In chronic large doses, depressed liver function and peptic ulcer activation. With IV administration, anaphylactic reactions (rarely) and hypotension (because of nicotinic acid's vasodilator affect). Many people will develop flushing, and heat sensation after taking a normal dose, on its own. This again, is due to the vasodilator properties of nicotinic acid.