A lack of which vitamin leads to symptoms such as glossitis, dementia, rough keratotic skin patches, and gastrointestinal disturbances?

Explanation

Niacin deficiency causes pellagra, which is characterized by the classic triad of dermatitis (rough, keratotic skin), diarrhea (gastrointestinal symptoms), and dementia (neurological symptoms), along with glossitis. Deficiencies of riboflavin, pyridoxine, and pantothenic acid do not typically present with this combination of signs.