Niacin (also known as vitamin B3 or nicotinic acid) is an organic compound with the formula C 6H 5NO 2 and, depending on the definition used, one of the 20 to 80 essential human nutrients. Pharmaceutical and supplemental niacin are primarily used to treat hypercholesterolemia (high cholesterol) and pellagra (niacin deficiency). ...
Niacin cannot be directly converted to nicotinamide, but both compounds are precursors of the coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) in vivo.[6] NAD converts to NADP by phosphorylation in the presence of the enzyme NAD+ kinase. NADP and NAD are coenzymes for many dehydrogenases, participating in many hydrogen transfer processes.[7] NAD is important in catabolism of fat, carbohydrate, protein, and alcohol, as well as cell signaling and DNA repair, and NADP mostly in anabolism reactions such as fatty acid and cholesterol synthesis.[7] High energy requirements (brain) or high turnover rate (gut, skin) organs are usually the most susceptible to their deficiency.[8] Although the two are identical in their vitamin activity, nicotinamide does not have the same pharmacological effects (lipid modifying effects) as niacin. Nicotinamide does not reduce cholesterol or cause flushing.[9] Niacin is involved in both DNA repair and the production of steroid hormones in the adrenal gland. ...
Tolerable upper intake levels (UL) for adult men and women is considered to be 35 mg/day by the Dietary Reference Intake system to avoid flushing. ...
Common psychiatric symptoms of niacin deficiency include irritability, poor concentration, anxiety, fatigue, restlessness, apathy, and depression.[14] Studies have indicated that, in patients with alcoholic pellagra, niacin deficiency may be an important factor influencing both the onset and severity of this condition. Patients with alcoholism typically experience increased intestinal permeability, leading to negative health outcomes. ...
Niacin is contraindicated with active liver disease, persistent elevated serum transaminases, active peptic ulcer disease, or arterial bleeding.
Pharmacological doses of niacin (1.5 – 6 g per day) lead to side effects that can include dermatological conditions such as skin flushing and itching, dry skin, and skin rashes including eczema exacerbation and acanthosis nigricans. ...
...doses above 2 g per day have been associated with liver damage, in particular, with slow-release formulations
Gastrointestinal complaints, such as dyspepsia (indigestion), nausea and liver toxicity fulminant hepatic failure, have also been reported.
Although high doses of niacin may elevate blood sugar, thereby worsening diabetes mellitus,[25] recent studies show the actual effect on blood sugar to be only 5–10%. Patients with diabetes who continued to take anti-diabetes drugs containing niacin did not experience major blood glucose changes. Thus overall, niacin continues to be recommended as a drug for preventing cardiovascular disease in patients with diabetes.
Hyperuricemia is another side effect of taking high-dose niacin, and may exacerbate gout.
Side effects of cardiac arrhythmias have also been reported.
Niacin in doses used to lower cholesterol levels has been associated with birth defects in laboratory animals, with possible consequences for infant development in pregnant women.
It reduces secondary outcomes associated with atherosclerosis, such as low density lipoprotein cholesterol (LDL), very low-density lipoprotein cholesterol (VLDL-C), and triglycerides (TG), but increases high density lipoprotein cholesterol (HDL).
Other effects include anti-thrombotic and vascular inflammation, improving endothelial function, and plaque stability.
The liver can synthesize niacin from the essential amino acid tryptophan, requiring 60 mg of tryptophan to make one mg of niacin.[48] Riboflavin, vitamin B6 and iron are required in some of the reactions involved in the conversion of tryptophan to NAD.
“Slow release” varieties have higher hepatotoxic activity, hence some types of prescription niacin are not recommended due to potential harm.
One form of dietary supplement is inositol hexanicotinate (IHN), which is inositol that has been esterified with niacin on all six of inositol's alcohol groups. IHN is usually sold as "flush-free" or "no-flush" niacin in units of 250, 500, or 1000 mg/tablets or capsules. It is sold as an over-the-counter formulation, and often is marketed and labeled as niacin, thus misleading consumers into thinking they are getting the active form of the medication. While this form of niacin does not cause the flushing associated with the immediate-release products, the evidence that it has lipid-modifying functions is contradictory, at best.
