Niacin (vitamin B3) deficiency (pellagra)

Niacin deficiency (pellagra)

Definition

Niacin (vitamin B3) has two principle forms: nicotinic acid and nicotinamide. Deficiency of niacin causes pellagra.

Aetiology

Niacin is found in plants, meat and fish. It can also be synthesised from tryptophan. Pellagra is seen in people with a predominantly maize diet, low in tryptophan. Other causes include increased tryptophan consumption in the carcinoid syndrome, prolonged use of isoniazid and Hartnup disease, an autosomal recessive congenital disorder with reduced absorption of tryptophan from the gut and reduced amino acid reuptake in the renal tubules.

Pathophysiology

Nicotinic acid is involved in energy utilisation. It is a precursor of nicotinamide, as in NAD and NADP, which are essential to glycolysis and oxidative phosphorylation. It is also used in maintaining skin, especially in sunexposed areas. Deficiency also causes villus atrophy in the small intestine.

Clinical features

Pellagra is due to lack of nicotinic acid, it often occurs as part of a more general nutritional deficiency. Pellagra presents with dermatitis, diarrhoea and dementia. Se vere, chronic deficiency may lead to encephalopathy and spasticity.

Management

Supplementation with nicotinic acid and treatment of other coexisting deficiencies.