Vitamin B3

Function

Mnemonic

Active forms of Niacin are NAD+ and NADP+.

Cofactor for redox reactions (e.g., alcohol dehydrogenase, isocitrate dehydrogenase, G6PD)

Therapeutic use

Dyslipidemia: Niacin lowers VLDL and increases HDL serum levels (See Lipid-lowering agents)

Vitamin B3 deficiency

Etiology

Malnutrition
Heavy drinking
Conditions associated with tryptophan deficiency
- Hartnup disease: decreased renal and intestinal tryptophan absorption
- Carcinoid syndrome (if metabolically active): increased tryptophan metabolism
Vitamin B6 deficiency (e.g., due to treatment with isoniazid): decreased niacin synthesis from tryptophan
Chronic consumption of grains that have not been processed by nixtamalization (common cause in developing countries)

Pathophysiology

Clinical features

Pasted image 20231104103822.png

Glossitis
Pellagra (caused by severe deficiency)
- Characteristic dermatitis
  - Circular broad collar rash on the neck (Casal necklace); affects dermatomes C3 and C4
  - Hyperpigmented skin lesions in sun-exposed areas (especially on the limbs)
- Diarrhea and vomiting
- Neurologic symptoms (e.g, dementia, hallucinations, anxiety, insomnia, encephalopathy)

Mnemonic

3 typical features of severe vitamin B₃ Deficiency: Dermatitis, Diarrhea, and Dementia.
3 for tree: dermatitis, dementia

Diagnostics

Treatment

Vitamin B3 toxicity

Facial flushing: due to prostaglandin release and NOT due to histamine (typically seen when niacin therapy is started, can be avoided by coadministration of aspirin)
Hyperuricemia, podagra
- Niacin decreases renal uric acid excretion.
Hyperglycemia