Niacin or nicotinic acid is also known as ‘ Pellagra Preventive factor’ of Goldberg. The coenzymes of niacin are NAD and NADP which are derived from the essential amino acid tryptophan.
The disease pellagra has been known for centuries. Pellagra is an Italian word the meaning of which is rough skin. But, its relation to the niacin vitamin deficiency in diet was established by Goldberger and his co scientists through an interesting experiment in jailed convicts.
Niacin is a pyridine derivative. To be specific it is pyridine – 3 – carboxylic acid. The amide form of niacin is known as niacinamide or nicotinamide. Dietary niacin, nicotinamide and tryptophan contribute to the synthesis of coenzymes of niacin namely nicotinamide adenine dinucleotide NAD+ and nicotinamide adenine dinucleotide phosphate NADP+. The nicotinamide is deaminated in the body to form niacin.
The coenzymes of niacin NAD+ and NADP+ are involved in a variety of oxidation and reduction reactions. They accept hydride ion and undergo reduction in the pyridine ring. This results in the neutralization of positive charges. The nitrogen atom and the fourth carbon atom of the niacinamide ring are involved in this reaction.
This reaction is reversed when NADH is converted into NAD+. A large number of enzymes (about 40) belonging to the class of oxido reductases are dependant on these coenzymes. These coenzymes are loosely bound to the apoenzymes and can be easily separated by dialysis.
These enzymes are very essential for the electron transport chain reactions.
Recommended dietary allowance RDA:
The daily requirement of niacin for an adult is15 – 25 mg and for children it is 10 – 15 mg. the requirement increases in pregnancy and lactation.
The natural sources include liver, yeast, cereals, pulses, whole grains, beans and pea nuts.
Milk, fish, egg and also vegetables contain niacin
The niacin deficiency results in a disease called pellagra. This disease involves skin, gastro intestinal tract, and central nervous system. The symptoms are three D’s namely dermatitis, diarrhea, and dementia and if left untreated it may rarely cause death.
It is mostly seen in individuals whose staple food is corn or maize as they contain low levels of niacin and tryptophan.
Therapeutic uses of niacin:
·Niacin inhibits lipolysis
·Triacyl glycerol synthesis in the liver is decreased.
·The serum LDL and VLDL are lowered
·Glycogen and fat reserves of skeletal and myocardial muscles are depleted
Blood glucose level and uric acid level increases