Niacin and Pellagra
Niacin (nicotinic acid and nicotinamide) is also known as vitamin B3. Both nicotinic acid and nicotinamide can serve as the dietary source of vitamin B3. Niacin is a pyridine carboxylic acid that is converted into an amide in the body.
Niacin is not a true vitamin in the strictest definition since it can be derived from the amino acid tryptophan. However, the ability to utilize tryptophan for niacin synthesis is inefficient (60 mg of tryptophan are required to synthesize 1 mg of niacin). Also, synthesis of niacin from tryptophan requires vitamins B1, B2 and B6 which would be limiting in themselves on a marginal diet.
Pellagra is clinically manifested by the 4 D’ s: photosensitive dermatitis, diarrhea, dementia, and death. The full tetrad of symptoms is usually not well-developed in infants and children. Pellagra is the most frequent clinical feature of nutritional deficiency in adults in rural populations in the Third World, whose staple diet is niacin deficient jawar or maize with inadequate animal protein, fruits and vegetables.
Primary pellagra results from inadequate nicotinic acid (i.e., niacin) and/or tryptophan intake in the diet. Secondary pellagra occurs when adequate quantities of niacin are present in the diet, but other diseases or conditions interfere with its absorption and/or processing.
Question of the day
A 56 – year-old male on Isoniazid therapy for tuberculosis has developed rashes on the exposed parts of the body. History is also suggestive of disoriented memory and diarrhea. The patient has been diagnosed with pellagra.
Pellagra is known to manifest in individuals deficient of niacin.
What is the correlation of Isoniazid therapy and niacin deficiency?
A. Isoniazid inhibits biological activation of niacin
B. Isoniazid prevents absorption of niacin
C. Isoniazid promotes excessive excretion of niacin
D. Isoniazid inhibits endogenous synthesis of niacin
E. Isoniazid acts a competitive inhibitor of niacin
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