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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.[2] The designation vitamin B3 also includes the corresponding amidenicotinamide, or niacinamide, whose chemical formula is C6H6N2O.
Deficiency and overdose
Chemical structure of nicotinamide.
Severe lack of niacin causes the deficiency disease pellagra, whereas a mild deficiency slows down the metabolism decreasing cold tolerance.
Niacin can have life-threatening acute toxic reactions[3]. One patient suffered vomiting after taking eleven 500-milligram niacin tablets over 36 hours, and another was unresponsive for several minutes after taking five 500-milligram tablets over two days.[4][5] Extremely high doses of niacin can cause niacin maculopathy, a thickening of the macula and retina which leads to blurred vision and blindness.[6]
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.[7]
Over 20 mg per day may cause flushing of the skin, lasting for about 15-30 minutes, sometimes accompanied by prickly or itching sensation. It may cause headache or nausea. This reaction is common[citation needed] in first-time users and is caused by the cells of the body releasing histamine, which results in vasodilation.[citation needed] When the body becomes used to the larger dose (usually over a period of days), these side effects may diminish or cease. Taking aspirin half an hour before the niacin will generally lessen the adverse effects.[citation needed] Slow or "sustained" release niacin supplement tablets are said to lessen side effects. Taking high doses of niacin may cause liver damage, particularly with slow-release formulations. High-dose niacin may also elevate blood sugar, thereby worsening diabetes mellitus. Hyperuricemia is another side effect of taking high-dose niacin; as such, it may worsen gout[citation needed].
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, done to avoid the perception that vitamins or niacin-rich food contain nicotine. 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."
Bioavailability
The liver can synthesize niacin from the essential amino acidtryptophan (see below), but the synthesis is extremely inefficient; 60 mg of tryptophan are required to make one milligram of niacin.[8] Dietary niacin deficiency tends to occur only in areas where people eat corn, the only grain low in niacin, as a staple food, and that don't use lime during maize (corn) meal/flour production. Alkali lime releases the tryptophan from the corn so that it can be absorbed in the intestine, and converted to niacin.[9]
Niacin plays an important role in the production of several sex and stress-related hormones, particularly those made by the adrenal gland. It also plays a role in removing toxic chemicals from the body.[9]
Niacin, when taken in large doses, increases the level of high density lipoprotein (HDL) or "good" cholesterol in blood, and is sometimes prescribed for patients with low HDL, and at high risk of heart attack.[10] An extended release formulation of niacin for this indication is marketed by Abbott Laboratories under the trade name Niaspan. Niacin (but not niacinamide) is also used in the treatment of hyperlipidemia because it reduces very low density lipoprotein (VLDL), a precursor of low density lipoprotein (LDL) or "bad" cholesterol, secretion from the liver, and inhibits cholesterol synthesis.[11] The main problem with the clinical use of niacin for dyslipidemia is the occurrence of skin flushing, even with moderate doses.[12] There are current attempts to create a prolonged-release formulation of the substance, to allow it to be used more often and more comfortably.[13]
^[1]Toxicity From the Use of Niacin to Beat Urine Drug Screening, Presented at the 8th Annual Clinical Pathological Case Presentation Competition, 2006 North American Congress of Clinical Toxicology (NACCT) meeting, October 2006, San Francisco, CA, Manoj K. Mittal, et al. published online 6 April 2007. doi:10.1016/j.annemergmed.2007.01.014
^[2]Hazards: Niacin to Pass a Drug Test Can Have Dangerous Results, By ERIC NAGOURNEY, New York Times, April 17, 2007
^Mittal MK, Florin T, Perrone J, Delgado JH, Osterhoudt KC. Toxicity From the Use of Niacin to Beat Urine Drug Screening. Ann Emerg Med. 2007 Apr 4. PMID17418450
^JD Gass, Nictonic Acid Maculopathy, Am. J. Opthamology, 1973;76:500-10
^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
