Pellagra is a nutritional deficiency disease caused by lack of niacin (vitamin B3) or its tryptophan precursor. It typically presents with the “three Ds”: dermatitis, diarrhea, and dementia, though advanced cases also involve neurological symptoms. The term originated in the early 20th century as researchers linked the condition to diet and vitamin deficiency. In modern medical usage, pellagra is rare in developed regions but remains a historical example of nutritional disease.
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