Nicotinamide– Biochemical Role & Effects of Deficiency

Nicotinic acid and Nicotinamide have similar physiological properties but it is the amide form in which this vitamin occurs in nature. Nicotinic acid, after ingestion, is converted to nicotinamide. Nicotinic acid is a vasodilator and produces flushing which is accompanied by a sensation of burning and itching. When given in large doses nicotinic acid lowers blood cholesterol. Nicotinamide does not possess these properties. Nicotinamide is heat stable. Nicotinic acid and nicotinamide have also been called niacin and niacinamide respectively. These compounds are mostly excreted in urine as their methyl derivatives. Their chemical structure are shown below:

   Occurrence of Nicotinamide

Liver (15 mg per 100 grams) and kidney are the richest sources. Meat, fish, eggs, milk, whole wheat, dried legumes, unpolished rice, peanuts, tomatoes, tea, coffee, green leafy vegetables are also good sources. In the body, it can be derived from tryptophan, 60 mg of which can supply 1 mg of the vitamin. The change, tryptophan à nicotinamide, occurs in many steps and takes place in the liver, gastrointestinal tract and other tissues of the body. Vitamin B6 is needed for the production of nicotinamide of from tryptophan. Intestinal bacteria also synthesize this vitamin.
Biochemical Role of Nicotinamide
Nicotinamide is a part of the structure of two coenzymes NAD and NADP whose roles as coenzymes in biological oxidation have already been discussed.

   Effects of Deficiency of Nicotinamide

Experimentally a nicotinamide deficiency produces symptoms in the dog, pig and monkey. In dogs this results in the condition known as black tongue and the dogs show apathy, pustular lesions in the mouth, severe salivation and bloody diarrhea. The dog stops eating the deficient diet.

In man, Pellagra (means rough skin) occurs; it is endemic in those areas where maize is the main diet and the intake of good quality protein is low. The disease is mostly found in women of child-bearing age and growing children. In India Pellagra has been found to occur in those regions where a lot maize is ingested.
Following body systems are affected:

  1. Skin: There is dermatitis, pigmentation and thickening of the skin. Skin lesions are symmetric and tend to be localized over exposed areas.
  2. Digestive system: Inflammation and smooth atrophy of the mucosa of the tongue and mouth, pain on swallowing, anorexia and diarrhea.
  3. Nervous System: This system is involved quite late. There is myelin degeneration in various regions of the spinal cord and cerebrum which leads to paresthesias and anesthesias. Mental disorders such as general nervousness, confusion, depression and insomnia are seen. Pellagra is most serious deficiency disease met with in the U.S.A.

The dermatitis, diarrhea and dementia which are the three prominent features of Pellagra are abbreviated as 3 Ds. Nicotinic acid and nicotinamide do not cure all the symptoms of Pellagra showing that Pellagra is not due solely to the deficiency of this vitamin; the deficiency of other B vitamin is also involved and in most cases a generalized malnutrition especially a deficiency of good quality proteins is present.

Factors Affecting its Requirement

The dietary requirement of this vitamin is less if more proteins are eaten because proteins have tryptophan which can form nicotinamide. Person mainly living on a maize diet need a higher dietary intake of this vitamin because maize is very poor in tryptophan.