Merck Manual

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Niacin Deficiency



Larry E. Johnson

, MD, PhD, University of Arkansas for Medical Sciences

Last full review/revision Oct 2019| Content last modified Oct 2019
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Niacin deficiency (causing pellagra) is uncommon in developed countries. Many people with niacin deficiency also have deficiencies of protein, riboflavin (a B vitamin), and vitamin B6.

  • A distinctive dark red rash appears on the hands, feet, calves, neck, and face, and the tongue and mouth turn dark red.

  • People have digestive tract problems, fatigue, insomnia, apathy, and later confusion and memory loss.

  • The diagnosis is based on the diet history, symptoms, and sometimes urine tests.

  • High doses of nicotinamide or nicotinic acid, taken by mouth, can correct the deficiency.

Niacin, a B vitamin, is essential for the processing (metabolism) of carbohydrates, fats, and many other substances in the body and for the normal functioning of cells.

Good sources of niacin include dried yeast, liver, red meat, poultry, fish, legumes, and whole-grain or enriched cereal products and bread. Foods rich in tryptophan (an amino acid), such as dairy products, can compensate for not consuming enough niacin in the diet because the body can convert tryptophan to niacin.

The term " niacin" is used in two ways: as a synonym for nicotinic acid and as a broader term that includes nicotinamide and nicotinic acid, two forms of this B vitamin.


One form of niacin deficiency results from a deficiency of niacin and tryptophan (an amino acid). This form causes a disorder called pellagra, which affects the skin, digestive tract, and brain. Pellagra develops only if the diet is deficient in niacin and tryptophan because the body can convert tryptophan to niacin. People who live in areas where maize (Indian corn) is the main food source are at risk of developing pellagra because maize is low in niacin and tryptophan. Furthermore, the niacin in maize cannot be absorbed in the intestine unless the maize is treated with alkali (as it is when tortillas are prepared). Pellagra may be a seasonal disorder, appearing each spring and lasting through the summer, when the diet consists mainly of maize products.

Pellagra also develops in people who have one of the following:

  • Hartnup disease, a rare hereditary disorder in which absorption of tryptophan is impaired

  • Carcinoid syndrome, a rare disorder in which tryptophan is not converted to niacin

The following can lead to a deficiency of niacin:


Typically, people with pellagra develop a symmetric, dark red rash that resembles a sunburn and becomes worse when it is exposed to sunlight (a condition called photosensitivity). The rash occurs in areas of sun exposure, and its location is distinctive:

  • On the arms and hands (like gloves)

  • On the feet and calves (like boots)

  • Around the neck (like a necklace)

  • On the face forming a butterfly shape

Skin abnormalities are persistent, and the affected areas may become brown and scaly.

The whole digestive tract is affected. The tongue and mouth may become inflamed and dark red. The tongue may swell, the mouth may burn, and sores may develop on both. The throat and esophagus may also burn. Saliva production may increase. Other symptoms include nausea, vomiting, abdominal discomfort, constipation, and diarrhea (which may be bloody).

Later, fatigue, insomnia, and apathy develop. Malfunction of the brain (encephalopathy) usually follows. It is characterized by confusion, disorientation, hallucinations, and memory loss. People may be overexcited, depressed, extremely elated (manic), delirious, or paranoid (thinking that people intend to harm them).


  • Physical examination

  • Urine tests

  • Relief of symptoms when niacin supplements are taken

The diagnosis of niacin deficiency is based on the diet history and symptoms. Measuring a by-product of niacin in urine can help establish the diagnosis, but this test is not always available.

The diagnosis is confirmed if niacin relieves symptoms.


  • Niacin supplements

  • Other B vitamin supplements

There are two types of niacin supplements: nicotinamide and nicotinic acid. Pellagra is treated with daily doses of nicotinamide taken by mouth. Nicotinamide, unlike nicotinic acid, does not cause flushing, itching, burning, or tingling sensations.

Because people with niacin deficiency often have other nutritional deficiencies, eating a balanced diet is important. Supplements of other B vitamins are also taken.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
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