Niacin is derived from the amino acid tryptophan.
Vitamin B6 plays a role in the conversion of tryptophan to niacin. Therefore, a deficiency of vitamin B6, which can be caused by isoniazid, can also manifest as a niacin deficiency.
Niacin is an essential component of nicotinamide adenine dinucleotide, NAD+, which is a coenzyme found in all living cells. This coenzyme is commonly used in oxidation reduction reactions.
Hartnup disease is a genetic disease which results in the inability of the kidneys to reabsorb amino acids, including tryptophan. This can cause a niacin deficiency because there is no tryptophan for conversion.
Carcinoid syndrome results from a metastatic carcinoid tumor, which actively secretes serotonin. Serotonin is also a derivative of tryptophan and can cause a niacin deficiency due to depletion of tryptophan.
Pellagra is the constellation of symptoms which is associated with severe niacin deficiency. It includes four D's of diarrhea, dermatitis, dementia, and death.
Diarrhea is a characteristic symptom of niacin deficiency.
Dermatitis is a characteristic symptom of niacin deficiency, and composes one of the "three D's" of pellagra.
Dementia is a characteristic symptom of niacin deficiency, and composes one of the "three-D's" of pellagra.
Glossitis can also be seen in niacin deficiency, as well as other B vitamin deficiencies.
Facial flushing is a common adverse reaction seen with patients taking niacin as medication. The flushing can be prevented with aspirin therapy.
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