Niacin (also known as vitamin B3, nicotinic acid and vitamin PP) is an organic compound with the formula C5H4NCO2H and, depending on the definition used, one of the between forty to eighty essential human nutrients.
This colourless, water-soluble solid is a derivative of pyridine, with a carboxyl group (COOH) at the 3-position. Other forms of vitamin B3 include the corresponding amide, nicotinamide ("niacinamide"), where the carboxyl group has been replaced by a carboxamide group (CONH2), as well as more complex amides and a variety of esters.
The terms niacin, nicotinamide, and vitamin B3 are often used interchangeably to refer to any member of this family of compounds, since they have the same biochemical activity.
Niacin is converted to nicotinamide and then to NAD and NADP ''in vivo''. Although the two are identical in their vitamin activity, nicotinamide does not have the same pharmacological effects as niacin, which occur as side effects of niacin's conversion.
Nicotinamide does not reduce cholesterol or cause flushing. Nicotinamide may be toxic to the liver at doses exceeding 3 g/day for adults.
Niacin is a precursor to NAD+/NADH and NADP+/NADPH, which play essential metabolic roles in living cells. Niacin is involved in both DNA repair, and the production of steroid hormones in the adrenal gland.
Niacin is one of five vitamins associated with a pandemic deficiency disease:
- niacin deficiency (pellagra)
- vitamin C deficiency (scurvy)
- thiamin deficiency (beriberi)
- vitamin D deficiency (rickets)
- vitamin A deficiency.
In larger doses, niacin can reverse atherosclerosis by lowering low-density lipoprotein (LDL) and favorably affecting other compounds.
The recommended daily allowance of niacin is 2–12 mg/day for children, 14 mg/day for women, 16 mg/day for men, and 18 mg/day for pregnant or breast-feeding women.
The upper limit for adult men and women is 35 mg/day, which is based on flushing as the critical adverse effect.
In general, niacin status is tested through urinary biomarkers, which are believed to be more reliable than plasma levels.
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Last Updated: Sep 15, 2014