• Introduction.• History.• Chemistry.• Co-enzyme forms.• Synthesis, Absorption, Transportation, Excretion• Sources• Useful Functions, NAD & NADP dependent

enzymes.• Recommended Daily allowance (RDA).• Deficiency Manifestations and Causes.• Hypervitaminosis

Niacin is a water-soluble vitamin, also known as vitamin B3.

Niacinamide is the active form of vitamin.

Warburg elucidated structure of NAD+ and won noble prize in 1931.Alexander Todd demonstrated function of NAD+ and won noble prize in 1957.NAD+ was originally called as Co-

Enzyme-1.

Niacin is pyridine-3-carboxylic acid. Niacinamide is the acid amide. In NAD+ and NADP+ , the reactive site is the 4th carbon atom and the nitrogen atom of the nicotinamide ring

There are two co-enzyme forms of niacin:1. NAD+ - Nicotinamide adenine dinucleotide.

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2. NADP+ -Nicotinamide adenine dinucleotide phosphate

The liver can synthesize niacin from the essential amino acid tryptophan, requiring 60 mg of tryptophan to make one mg of niacin. Riboflavin, vitamin B6 and iron are required in some of the reactions involved in the conversion of tryptophan to NAD.

Absorption of nicotinic acid and nicotinamide from the stomach and the intestine is rapid and at low concentrations is mediated by sodium ion-dependent facilitated diffusion. At higher concentrations, passive diffusion predominates.

Nicotinamide is transported to tissues to be used in synthesis of NAD when needed. Both forms of the vitamin enter cells by simple diffusion; however, both nicotinic acid and nicotinamide also enter erythrocytes by facilitated transport.

Excess niacin is methylated in the liver to N1-methyl-nicotinamide, which is excreted in the urine along with the 2- and 4-pyridone oxidation products of N1-methyl-nicotinamide. The two major excretion products are N1-methyl-nicotinamide and its pyridone derivative. The proportions differ somewhat depending on the amount and form of niacin ingested and the niacin status of the individual.

Animal products:Chicken-(6.5 mg)beef (5 – 6 mg)fish (2.5 – 13 mg)eggs (0.1 mg)

Fruits and vegetables:Avocados (1 mg)Dates (2 mg)Tomatoes (0.7 mg)leaf vegetables (0.3 - 0.4 mg)Broccoli (0.6 mg)Carrots (0.3 - 0.6 mg)Sweet potatoes (0.5mg)…continued

Other Sources:Red Bull Energy Drink (28 mg per 12 ounces)Peanut butter (15 mg)Mushrooms (3.5 – 4 mg)Soy sauce (0.4 mg)nuts (2 mg)

•NIACIN THE CRAB CONVERTOR: A major function is that it assists other types of B vitamins in converting carbohydrates to glucose (a source of energy for the body) and in metabolizing fats.• One of the most important function of niacin is that it helps in maintaining good cardiovascular health. It can regulate cholesterol and serum triglyceride concentrations in system. It can also increase HDL’s.•Niacinamide and other forms of niacin has been found to also help alleviate the symptoms of arthritis.

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•Niacin shows great potential in cure for Alzheimer’s disease. •Healthy eyesight can also be a benefit of niacin•NAD+ may also be added onto cellular RNA as a base modification to form poly(ADP-ribose) structure, which is involved in the regulation of several cellular events and is most important in the cell nucleus, in processes such as DNA repair and telomere maintenance.

•Lactate dehydrogenase. •Glyceraldehyde-3-phosphate dehydrogenase.•Pyruvate dehydrogenase.[Pyruvate Acetyl CoA] •α ketoglutarate dehydrogenase. [alpha ketoglutarate Succinyl CoA]• β hydroxyacyl CoA dehydrogenase. [Beta hydroxyacyl CoA Beta ketoacyl CoA].

•Glucose-6-Phosphate dehydrogenase.[Glucose-6-Phospahte 6-Phospho-glucono lactone].•6-phospho gluconate dehydrogenase.[6-phospho gluconate 3-keto-6-phospho gluconate].•Cytoplasmic isocitrate dehydrogenase.•Malic [malate pyruvate]

Children: Adults: Lactating stage:0-3months-(3mg) Males: 19-50yrs-(17mg) +2mg1-3yrs-(8mg) Females: 19-50yrs(13mg)7-10yrs(12mg)

Pellagra is a clinical condition caused by deficiency of Niacin as well as Tryptophan. Pellagra means Rough Skin. Pellagra is characterized by a photosensitive dermatitis. As the condition gets worse there is dementia as well as diarrhea. Untreated pellagra is fatal. Although the nutritional etiologyof pellagra is well established, and tryptophan or niacin prevents or cures the Disease. Additional factors, including deficiency of riboflavin or vitamin B6,both of which are required for synthesis of nicotinamide from tryptophan, may be important. In most outbreaks of pellagra, twice as many women as men are affected, probably the result of inhibition of tryptophan metabolism by estrogen metabolites.

A number of genetic diseases that result in defects of tryptophan metabolism are associated with the development of pellagra, despite an apparently adequate intake of both tryptophan and niacin are:

• Hartnup Disease: Tryptophan absorption from intestine is defective in this congenital disease. Moreover, tryptophan is excreted in urine in large quantities. This leads to lack of tryptophan and consequently defeiency of nicotinamide.

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• Carcinoid Syndrome: The tumor utilises major portion of available tryptophan for the synthesis of serotonin, so tryptophan is unavailable.

•Isoniazid (INH): It is an antituberculous drug, which inhibits pyridoxal phosphate formation. Hence, there is block in conversion of tryptophan to NAD+.

Nicotinic acid when given orally or parenterally produces a transient vasodilatation of the cutaneous vessels and Histamine release. The reaction is accompanied by itching, burning, and tingling. Intake of nicotinic acid in excess of 50mg/day may lead to liver damage.