Niacin, a member of the B vitamin family, is the term
used for both nicotinic acid and nicotinamide. These two compounds have
identical vitamin activities but are different in their pharmacological
activities.
Nicotinic acid, in pharmacological doses, is used as an antihyperlipidemic agent while nicotinamide may have anti-diabetogenic activity.
Niacin is active as nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which serve as coenzymes.
Niacin is water-soluble, stable under acidic and alkali conditions and resistant to light and oxidation.
Niacin's biochemical effects are principally mediated by its metabolite nicotinamide adenine dinucleotide (NAD+).
Both nicotinic acid and nicotinamide are efficiently absorbed from the stomach and small intestine with almost complete absorption of doses up to 3-4 g.
Tryptophan is converted to niacin with 60 mg of tryptophan equivalent to 1mg of niacin. This is termed niacin equivalent.
Niacin, through its metabolites, is involved in a variety of biological processes including:
Energy production; NAD+, a niacin metabolite, is used in metabolic reactions to transfer the potential free energy stored in carbohydrate, fat and protein to NADH, which is used to form ATP.
The regulation of gene expression and the maintenance of genomic activity.
Synthesis of fatty acids, cholesterol and steroids, NADPH (the reduced form of NADP+), serves as the reducing agent in fatty acid and steroid biosyntheses. It also serves to maintain glutathione in its reduced form.
NAD+ and NADP+ are both involved in the biosyntheses of signaling molecules.
Male 9 to 13 years 14 to 18 years 19+ years Female 13 to 19 years 14 to 18 years 19+ years
12 16 16
12 14 14
20 30 35
20 30 35
Pregnancy <= 18 years 19 to 50 years
18 18
30 35
Lactation <= 18 years 19 to 50 years
17 17
30 35
* Values are Adequate Intakes (AI), others are RDA. DRI for niacin based on niacin equivalents (NE); 1 mg niacin = 60 mg tryptophan; 0 - 6 months is preformed niacin and not NE. ND: Not determinable due to lack of data of adverse effects
in this age group and concern with regard to lack of ability to handle excess
amounts.
High doses of nicotinic acid (usually used for hyperlipidemia treatment) can cause a flush, resulting in vasodilation of cutaneous blood vessels. This will increase blood flow, principally in the face, neck and chest. Nicotinamide is not associated with this condition.
Symptoms of flushing include a burning, tingling and itching sensation and are often accompanied by pruritus and headaches.
High doses of nicotinic acid can be toxic to the liver, particularly in those taking the slow-release form.
High doses of nicotinic acid have caused impaired glucose tolerance in healthy individuals and vision and eye related problems.
Nicotinic acid is effective in lowering cholesterol and triacylglycerols. It has been found to significantly decrease
cardiovascular and cerebrovascular events in those with coronary heart disease.
Niacin is reported to potentiate the hypotensive effects of ganglionic blocking drugs. It is advisable to avoid concomitant administration of the drug and the herb.
The long-term use of isoniazid [INH], an antimycobacterial agent, may interfere with the conversion of dietary tryptophan to niacin. This increases the required dose of niacin.
Patients taking HMG-CoA reductase inhibitors, such as lovastatin [Mevacorâ] and simvastatin [Zocorâ], to treat hypercholesterolemia, and more than 1g daily of niacin, increase the risk of developing myopathy and rhabdomyolysis. However, patients who take extended-release niacin [Niaspanâ] with various HMG-CoA reduction inhibitors, have less risk of rhabdomyolysis. Patients should consult their physician before taking niacin supplements with these medications.
Information on the relationship between substances and disease is provided for general information, in order to convey a balanced review of the scientific literature. In many cases the relationship between a substance and a disease is tentative and additional research is needed to confirm such a relationship.
Heart disease: Niacin is
used in therapeutic doses to treat various forms of hyperlipidemia. Niacin has
been shown to be effective in lowering plasma triacylglycerol and LDL
concentrations, while raising plasma HDL concentrations. Mechanism of action by
niacin differs from lipid-lowering medications, giving the rationale for
combination therapy for complete lipid goal achievement. 6
In a clinical study, patients with >200 mg/dl total cholesterol were
randomly assigned 10 mg atorvastatin or immediate-release niacin, 3000 mg,
daily for 12 weeks. Both treatments reduced plasma VLDL and LDL
concentrations. Niacin also increased plasma HDL concentrations.
7
Diabetes: Gardner and
colleagues administered 20 mg pravastatin once daily to 23 diabetic outpatients
for 4 weeks. After reassessment, niacin was added (maximum of 500 mg TID) to
certain outpatients' regimens. Results showed that addition of niacin to
pravastatin therapy significantly lowered plasma LDL concentrations vs.
pravastatin alone. Low dose niacin is a promising addition in the treatment of
hypercholesterolemia in patients with both types I and II diabetes
mellitus.8
The dietary supplement information contained on this site has been compiled from published sources thought to be reliable, but it cannot be guaranteed. Efforts have been made to assure this information is accurate and current. However, some of this information may be purported or outdated due to ongoing research or discoveries. The authors, editors and publishers cannot accept responsibility for errors or omissions or for any consequences from applications of the information in this site and make no warranty, expressed or implied, with respect to the contents herein.
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