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
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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