Niacin, or vitamin B3, is a water-soluble B vitamin that occurs naturally in some foods, is added to foods and is sold as food supplements. The two distinct forms of niacin in food and supplements are nicotinic acid and nicotinamide. The body can also convert tryptophan, an amino acid, into nicotinamide. Because niacin is water-soluble, any excess the body does not need is excreted in the urine. Niacin works in the body as a coenzyme, with more than 400 enzymes depending on it for various reactions. Niacin helps convert nutrients into energy, make cholesterol and fats, create and repair DNA, and exert antioxidant effects.
What are the recommended amounts of vitamin B3?
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 aged 19 and over is 16 mg NE for men, 14 mg NE for women, 18 mg NE for pregnant women and 17 mg NE for breastfeeding 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 over 19 is 35 milligrams.
Food sources
Niacin deficiency is rare because niacin is found in many foods, both animal and plant-based.
- Red meat: beef, beef liver, pork
- Poultry
- Fish
- Brown rice
- Fortified cereals and breads
- Nuts and seeds
- Legumes
- Bananas
Food supplements
Niacin is available as a supplement in the form of nicotinic acid or nicotinamide. Sometimes supplements contain amounts well above the RDA, which can cause unpleasant side effects such as flushing. Niacin supplements are also available as a prescription medicine to treat high cholesterol; this is usually an extended-release form of nicotinic acid that is absorbed more slowly and gradually, so it does not cause flushing. Because of the very high doses of nicotinic acid required, up to 2,000 mg a day, this supplement should only be used under medical supervision.
Read also: What is the role of iron?
Signs of deficiency and toxicity
Deficiency
Niacin deficiency is rare in the United States and other industrialised countries, because niacin is well absorbed from most foods (except certain cereal grains, in which niacin is bound to fibre, reducing its absorption) and is added to many foods and multivitamins. Severe niacin deficiency leads to pellagra, a condition that causes a dark, sometimes scaly rash on areas of skin exposed to the sun, a bright red tongue and constipation/diarrhoea. Other signs of severe niacin deficiency include:
- Depression
- Headaches
- Fatigue
- Memory loss
- Hallucinations
Groups at risk of deficiency
Restricted diets. People whose diet is limited in the variety and quantity of foods, such as those living in poverty or who are very ill and cannot eat a balanced diet, are at greater risk. Developing countries whose diets are based mainly on maize are at risk of pellagra, as maize is low in absorbable niacin and tryptophan. Chronic alcoholism. Excessive alcohol consumption reduces the absorption of several nutrients, particularly water-soluble vitamins, including those in the B family.
Carcinoid syndrome. This is a disease involving slow-growing cancer cells in the intestine that release a chemical called serotonin. The syndrome causes tryptophan from food to be converted into serotonin rather than niacin, increasing the risk of low niacin levels.
Toxicity
Toxicity from eating foods that contain niacin is very rare, but it is possible. It can occur with long-term use of high-dose supplements. Reddening of the skin with itching or tingling on the face, arms and chest is a common sign. Flushing occurs mainly when taking high-dose supplements in the form of nicotinic acid rather than nicotinamide.
Other signs:
- Dizziness
- Low blood pressure
- Fatigue
- Headaches
- Stomach ache
- Nausea
- Blurred vision
- Impaired glucose tolerance and liver inflammation in severe cases (at very high doses of 3,000 to 9,000 mg a day for several months or years).
Vitamin B3: did you know?
Many B vitamins, including niacin, are thought to help boost energy. Because niacin is water-soluble (which reduces the risk of it building up to toxic levels in the body), many people readily take supplements containing up to 100 times the RDA for this vitamin. Although niacin helps several enzymes turn food into ATP, a form of energy, taking doses far above the RDA will not give you any extra energy boost. A balanced diet made up of a variety of foods is often all you need to benefit from niacin’s positive effects on energy.
Maize is naturally rich in niacin, but it is bound to carbohydrates, which makes it hard for the human body to absorb. However, when maize is nixtamalised (a traditional tortilla-making process in which the maize is treated with calcium hydroxide, cooked and ground), the calcium hydroxide treatment makes the niacin absorbable.
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