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Chapter: Biochemistry: Vitamins

Niacin (B3)

Niacin is pyridine-3-carboxylic acid (Fig. 8.7). It occurs in tissues as nicotinamide.

Niacin (B3)

Niacin is pyridine-3-carboxylic acid (Fig. 8.7). It occurs in tissues as nicotinamide.


Niacin is required for the stepwise breakdown of glucose to yield energy. Niacin is essential for the healthy skin, normal functions of the gastro intestial tract and maintenance of the nervous system.


The meat group especially organ meats and poultry, is the chief source of preformed niacin. Dark green leafy vegetables, whole grain, enriched breads and cereals are fair sources.

Niacin is more stable to cooking procedures than thiamine or ascorbic acid (Vitamin C).


The recommended niacin allowance is 6.6 mg/1000 k cal. This can be supplied by exogenous niacin in the diet and by the tryptophan, an essential aminoacid that is the precursor of niacin biosynthesis.

Infants - 5 -8 mg / day

Children - 9 - 16 mg / day

Adults male - 16 - 20 mg/day

Adults female - 12 - 16 mg/day

Pregnant women - 14 - 18 mg/day

Lactating women - 16 - 20 mg / day

Absorption and storage

Nicotinic acid and nicotinamide are absorbed from the intestine through the portal vein into the general circulation. Excess nicotinic acid is not stored in the body.


Pellagra is the major deficiency disease resulting from the lack of niacin. Dermatitis, especially of the skin exposed to the sun, soreness of the mouth, swelling of the tongue, diarrohea, and mental changes including depression, confusion, disorientation, and delirium are typical of the advancing stages of the disease, which ends to death if not treated. (The disease is sometimes referred to as the “4D’S” - dermatitis, diarrohea, dementia and death).

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