pellagra, deficiency disease due to a lack of niacin (nicotinic acid), one of the components of the B complex vitamins in the diet. Niacin is plentiful in yeast, organ meats, peanuts, and wheat germ. The disease manifests itself in lesions of the skin and mucous membrane, diarrhea and other gastrointestinal symptoms, neurological derangement, and mental confusion. It is most common in areas where the diet consists mainly of corn, which, unlike other grains, lacks niacin as well as the amino acid tryptophan, which the body uses to synthesize the vitamin. Treatment includes large doses of niacin and the institution of a proper diet to prevent recurrences.

Nutritional disorder caused largely by a deficiency of niacin, marked by skin lesions and digestive and neurological disturbances. Dermatitis usually appears first, with abnormal sensitivity to sunlight. It may look like a severe sunburn, later becoming reddish brown, rough, and scaly. Diarrhea usually alternates with constipation, along with mouth and tongue inflammation and cracking and dry scaling of the lips. Later, mental abnormalities may include nervousness, depression, and delirium. Mild cases of niacin deficiency respond to a well-balanced diet alone. Pellagra still occurs where diets consist mostly of corn, which is low in both niacin and tryptophan (converted to niacin in the body), with little or no protein-rich food. It can also be a side effect of chronic alcoholism.

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