Niacin

Niacin, also known as nicotinic acid or vitamin B3, is a water-soluble vitamin whose derivatives such as NADH, NAD, NAD+, and NADP play essential roles in energy metabolism in the living cell and DNA repair. The designation vitamin B3 also includes the amide form, nicotinamide or niacinamide, whose chemical formula is C6H6N2O. Severe lack of niacin causes the deficiency disease pellagra, wherein a mild deficiency slows down the metabolism decreasing cold tolerance. The recommended daily allowance of niacin is 2-12 mg a day for children, 14 mg a day for women, 16 mg a day for men, and 18 mg a day for pregnant or breast-feeding women.

Discovery

Nicotinic acid was first discovered from the oxidation of nicotine. When the properties of nicotinic acid were discovered, it was thought prudent to choose a name to dissociate it from nicotine and to avoid the idea that either smoking provided vitamins or that wholesome food contained a poison. The resulting name 'niacin' was derived from nicotinic acid + vitamin. Vitamin B3 is also referred to as "vitamin PP", a name derived from the obsolete term "pellagra-preventing factor."

Industrial use

Nicotinic acid reacts with haemoglobin 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. Niacin is licensed as a food colouring agent in some, non-European, countries.

Bioavailability

The liver can synthesize niacin from the essential amino acid tryptophan (see below), but the synthesis is extremely slow and requires vitamin B6; 60 mg of tryptophan are required to make one milligram of niacin. Bacteria in the gut may also perform the conversion but are inefficient. For this reason, eating lots of tryptophan is not an adequate substitute for consuming niacin. However, this explains why pellagra requires a deficiency of protein as well as niacin.

Other uses

Some information in this article or section has not been verified and may not be reliable.
Please check for any inaccuracies, and modify and cite sources as needed.
Because niacin promotes metabolism, some believe that taking large doses will speed up the elimination of THC from the body and produce a negative result for marijuana on a drug test. There is no evidence that this is effective, however no evidence has been provided to the contrary. Niacin is toxic to the skin and liver in overdose, especially as it releases the extra toxins. Studies in laboratory animals have demonstrated behavioural changes when large doses of niacin are given. Sullivan, WT (June 10, 1958). "behavioural changes in rats and guinea pigs induced by the administration of indole 3-acetic acid and 6-aminonicotinamide". The Journal of Nutrition: 199-209. Retrieved on September 4, 2006. There is evidence that doses of 500-1000mg can terminate a bad trip on LSD, a synthetic indole, or enhance the MDMA experience.

Niacin in large doses is also known to increase the level of HDL (good) cholesterol in blood, and is often prescribed for patients with low HDL, and consequently high risk of heart attack.

Niacin is used in the treatment of hyperlipidemia because it reduces VLDL secretion from the liver and inhibits cholesterol synthesis. There are two ways to reduce cholesterol levels, either by reducing dietary intake of cholesterol, or by decreasing cholesterol synthesis, for example with Niacin supplementation. Since VLDL is a precursor of LDL (bad cholesterol), LDL levels decrease with Niacin treatment. The main side effect is cutaneous flushing. [Katzung and Trevors Pharmacology Examination and Board Review 7th edition, Authors: Trevor, Anthony J. Katzung, Bertram G. and Masters, Susan B., Lange Medical Books/ McGraw-Hill 2005]

Biosynthesis

The 5-membered aromatic heterocycle of the essential amino acid, tryptophan, is cleaved and rearranged with the alpha amino group of tryptophan into the 6-membered aromatic heterocycle of niacin. By the following reaction:

Tryptophan --> Kynurenine --> 3-hydroxy kynurenine

  • --(B6 enzyme needed)--> Niacin

    (

  • ) from this intermediary xanthurenic acid is formed

    Biosynthesis: tryptophan -> kynurenine -> niacin

    Food Sources

    Animal products: Plant Products: Fungi:
    liver, heart and kidney
    chicken
    fish: tuna, salmon
    milk
    eggs
    Fruits and vegetables:

    leaf vegetables
    broccoli
    tomatoes
    carrots
    dates
    sweet potatoes
    asparagus
    avocados
    Seeds:

    nuts
    whole grain products
    legumes
    saltbush seeds

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