Niacin – Vitamin B3

A range of foods high in Niacin (or Vitamin B3) including legumes, nuts, seeds, carrots, chicken, avocado, eggs, grains, broccoli

Niacin, or vitamin B3, is a water-soluble B vitamin found naturally in some foods, added to foods, and sold as a supplement. The two most common forms of niacin in food and supplements are nicotinic acid and nicotinamide. The body can also convert tryptophan—an amino acid—to nicotinamide. Niacin is water-soluble so that excess amounts the body does not need are excreted in the urine. Niacin works in the body as a coenzyme, with more than 400 enzymes dependent on it for various reactions. Niacin helps to convert nutrients into energy, create cholesterol and fats, create and repair DNA, and exert antioxidant effects. [1,2] 

Recommended Amounts

RDA:  Niacin is measured in milligrams (mg) of niacin equivalents (NE). One NE equals 1 milligram of niacin or 60 mg of tryptophan. The Recommended Dietary Allowance (RDA) for adults 19+ years is 16 mg NE for men, 14 mg NE for women, 18 mg NE for pregnant women, and 17 mg NE for lactating women.

UL:  The Tolerable Upper Intake Level is the maximum daily intake unlikely to cause harmful effects on health. The UL for niacin for all adults 19+ years is 35 milligrams. 

Niacin and Health

Food Sources

A niacin deficiency is rare because it is found in many foods, both from animals and plants.


Niacin is available as a supplement in the form of nicotinic acid or nicotinamide. Sometimes the amounts in supplements are far beyond the RDA, causing unpleasant side effects of flushing. Niacin supplements are also available as a prescription medicine that is used to treat high cholesterol; this typically comes in an extended release form of nicotinic acid that allows slower, more gradual absorption so that it does not cause flushing. Because of the very high doses of nicotinic acid needed, up to 2,000 mg daily, this supplement should only be used when monitored by a physician. 

Signs of Deficiency and Toxicity


A niacin deficiency is rare in the United States and other industrialized countries because it is well-absorbed from most foods (with the exception of some cereal grains in which niacin is bound to its fibers, decreasing the absorption) and is added to many foods and multivitamins. A severe niacin deficiency leads to pellagra, a condition that causes a dark, sometimes scaly rash to develop on skin areas exposed to sunlight; bright redness of the tongue; and constipation/diarrhea. Other signs of severe niacin deficiency include:

  • Depression
  • Headache
  • Fatigue
  • Memory loss
  • Hallucinations

Groups at risk for deficiency

  • Limited diets. People whose diets are limited in both variety and quantity of foods, such as those living in poverty or who are very ill and cannot eat a balanced diet, are at increased risk. Developing countries that eat corn or maize as a main food source are at risk for pellagra, as these foods are low in both absorbable niacin and tryptophan.
  • Chronic alcoholism. The absorption of several nutrients, particularly water-soluble vitamins including the B family, is decreased with excessive alcohol intake.
  • Carcinoid syndrome. This is a disease of slow-growing cancer cells in the gut that release a chemical called serotonin. The syndrome causes tryptophan in the diet to be converted into serotonin rather than niacin, which increases the risk of decreased niacin.


Toxicity when eating foods containing niacin is rare, but can occur from long-term use of high-dose supplements. A reddened skin flush with itchiness or tingling on the face, arms, and chest is a common sign. Flushing occurs mainly when taking high-dosage supplements in the form of nicotinic acid, rather than nicotinamide. Niacin taken in large doses as supplements may also increase uric acid levels, which is a risk factor for gout.

Other signs:

  • Dizziness
  • Low blood pressure
  • Fatigue
  • Headache
  • Upset stomach
  • Nausea
  • Blurred vision
  • Impaired glucose tolerance and inflammation of liver in severe cases (at very high doses of 3,000-9,000 mg daily for several months/years) [1] 

Did You Know?

  • Many B vitamins are thought to help increase energy, including niacin. Because niacin is water-soluble (less risk of building up in the body to a toxic level), many people don’t think twice about taking a supplement that may contain 100 times the RDA for the vitamin. Although niacin assists several enzymes in converting food into ATP, a form of energy, taking doses well beyond the RDA will not offer a special boost in energy levels. Eating a balanced diet with a variety of foods is often all that is needed to obtain niacin’s energy-boosting benefit.
  • Corn is naturally high in niacin, but it is bound to carbohydrates which makes it difficult for the human body to absorb. However, when corn is nixtamalized (a traditional process in tortilla making where corn is treated with calcium hydroxide, cooked, and ground) the niacin becomes absorbable because of the calcium hydroxide treatment.


B Vitamins
Vitamins and Minerals

Last reviewed March 2023

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