Niacin, another vitamin of B-complex group, is found in the body in two forms, niacin and proniacin. It is readily absorbed in the small intestine but only a meager amount is stored in the body. Thus a day-to-day supply of niacin is needed by the body. Any excess of niacin is excreted in the urine. Milk and wheat protein contain sufficient tryptophan to compensate for a diet which is deficient in niacin. Deficiency of niacin and its precursor tryptophan expresses itself in the form of ‘pellagra’. This deficiency is usually associated with a diet based chiefly on corn and inadequate amounts of tryptophan containing proteins.
People consuming milk rarely show any sign of pellagra because the body converts tryptophan (proniacin) to niacin. On the other hand corn protein is deficient in trytophan and is no protection against pellagra.
Causes of Niacin Deficiency
In olden times the 3 M’s (fatty pork meat, maize and molasses) were considered to be the cause of pellagra. Corn and maize (protein food) have niacin in the bound form thus very little niacin is available. Hence pellagra is common in countries where corn is the staple food.
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(i) Long standing poor dietary habits of individuals are one cause. A low protein diet with the glaring absence of fresh fruits, vegetables, lean meat, eggs and milk leads to niacin deficiency.
(ii) Individuals afflicted with diseases which interfere with appetite or with the absorption and utilization of food. Thus niacin deficiency may be found in chronic diarrhea, malabsorption diseases, tuberculosis and in disease states in which the metabolism is elevated.
(iii) Chronic alcoholism is another causative factor for pellagra. Habitual long standing dietary neglect is very often found in this group.
(iv) The intake of antibiotics interferes with the absorption of niacin from the intestine. Antibiotics further kill the intestinal flora that synthesise B group vitamins. Due to a deficiency of Vitamin B, the body is unable to convert tryptophan into niacin, resulting in pellagra.
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(v) Sunlight and heavy work appear to precipitate pellagra that appears as a rash on exposed parts.
In India pellagra is caused in population groups that consume a large quantity of jowar as well as maize. Jowar has a very high leucine (amino acid) content that interferes with the metabolism of niacin and tryptophan, causing pellagra.