Niacin (vitamin B3) is a type of B vitamin. It is water-soluble vitamin. It is not stored in the body. Water-soluble vitamins dissolve in water. Leftover amounts of the vitamin leave the body through the urine. The body keeps a small reserve of these vitamins. They have to be taken on a regular basis to maintain the reserve. Niacin helps the digestive system, skin, and nerves to function. It is also important for changing food to energy.
Niacin (also known as vitamin B3) is one of the water-soluble B vitamins. Niacin is the generic name for nicotinic acid (pyridine-3-carboxylic acid), nicotinamide (niacinamide or pyridine-3-carboxamide), and related derivatives, such as nicotinamide riboside [1-3]. Niacin is naturally present in many foods, added to some food products, and available as a dietary supplement.
All tissues in the body convert absorbed niacin into its main metabolically active form, the coenzyme nicotinamide adenine dinucleotide (NAD). More than 400 enzymes require NAD to catalyze reactions in the body, which is more than for any other vitamin-derived coenzyme . NAD is also converted into another active form, the coenzyme nicotinamide adenine dinucleotide phosphate (NADP), in all tissues except skeletal muscle .
NAD and NADP are required in most metabolic redox processes in cells where substrates are oxidized or reduced. NAD is primarily involved in catabolic reactions that transfer the potential energy in carbohydrates, fats, and proteins to adenosine triphosphate (ATP), the cell’s primary energy currency . NAD is also required for enzymes involved in critical cellular functions, such as the maintenance of genome integrity, control of gene expression, and cellular communication [3,4]. NADP, in contrast, enables anabolic reactions, such as the synthesis of cholesterol and fatty acids, and plays a citical role in maintaining cellular antioxidant function.
Most dietary niacin is in the form of nicotinic acid and nicotinamide, but some foods contain small amounts of NAD and NADP. The body also converts some tryptophan, an amino acid in protein, to NAD, so tryptophan is considered a dietary source of niacin.
When NAD and NADP are consumed in foods, they are converted to nicotinamide in the gut and then absorbed . Ingested niacin is absorbed primarily in the small intestine, but some is absorbed in the stomach [1-3].
Even when taken in very high doses of 3–4 g, niacin is almost completely absorbed. Once absorbed, physiologic amounts of niacin are metabolized to NAD. Some excess niacin is taken up by red blood cells to form a circulating reserve pool. The liver methylates any remaining excess to N1-methyl-nicotinamide, N1-methyl-2-pyridone-5-carboxamide, and other pyridone oxidation products, which are then excreted in the urine. Unmetabolized nicotinic acid and nicotinamide might be present in the urine as well when niacin intakes are very high.
Levels of niacin in the blood are not reliable indicators of niacin status. The most sensitive and reliable measure of niacin status is the urinary excretion of its two major methylated metabolites, N1-methyl-nicotinamide and N1-methyl-2-pyridone-5-carboxamide . Excretion rates in adults of more than 17.5 micromol/day of these two metabolites reflect adequate niacin status, while excretion rates between 5.8 and 17.5 micromol/day reflect low niacin status. An adult has deficient niacin status when urinary-excretion rates are less than 5.8 micromol/day. Indicators of inadequacy such as this and other biochemical signs (e.g., a 2-pyridone oxidation product of N1-methyl-nicotinamide below detection limits in plasma or low erythrocyte NAD concentrations) occur well before overt clinical signs of deficiency . Another measure of niacin status takes into account the fact that NAD levels decline as niacin status deteriorates, whereas NADP levels remain relatively constant [1,3,5]. A “niacin number” (NAD/[NAD + NADP] concentrations in whole blood x 100) below 130 suggests niacin deficiency [6,7]. A “niacin index” (the ratio of erythrocyte NAD to NADP concentrations) below 1 suggests that an individual is at risk of developing niacin deficiency . No functional biochemical tests that reflect total body stores of niacin are available .
Intake recommendations for niacin and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by an expert committee of the Food and Nutrition Board (FNB) at the National Academies of Sciences, Engineering, and Medicine . DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and sex, include:
- Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals.
- Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA.
- Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals; usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them; can also be used to assess the nutrient intakes of individuals.
- Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.
Table 1 lists the current RDAs for niacin as mg of niacin equivalents (NE) . The FNB defines 1 NE as 1 mg niacin or 60 mg of the amino acid tryptophan (which the body can convert to niacin). Niacin RDAs for adults are based on niacin metabolite excretion data. For children and adolescents, niacin RDAs are extrapolated from adult values on the basis of body weight. The AI for infants from birth to 6 months is for niacin alone, as young infants use almost all the protein they consume for growth and development; it is equivalent to the mean intake of niacin in healthy, breastfed infants. For infants aged 7-12 months, the AI for niacin is in mg NE and is based on amounts consumed from breast milk and solid foods.
|Birth to 6 months*||2 mg||2 mg|
|7–12 months*||4 mg NE||4 mg NE|
|1–3 years||6 mg NE||6 mg NE|
|4–8 years||8 mg NE||8 mg NE|
|9–13 years||12 mg NE||12 mg NE|
|14–18 years||16 mg NE||14 mg NE||18 mg NE||17 mg NE|
|19+ years||16 mg NE||14 mg NE||18 mg NE||17 mg NE|
* Adequate Intake
Am I getting enough niacin?
Most people in the United States get enough niacin from the foods they eat. Niacin deficiency is very rare in the United States. However, some people are more likely than others to have trouble getting enough niacin:
- Undernourished people with AIDS, alcohol use disorder, anorexia, inflammatory bowel disease, or liver cirrhosis
- People whose diet has too little iron, riboflavin, or vitamin B6; these nutrients are needed to convert tryptophan to niacin
- People with Hartnup disease, a rare genetic disorder
- People with carcinoid syndrome, a condition in which slow-growing tumors develop in the gastrointestinal tract
What happens if I don’t get enough niacin?
You can develop niacin deficiency if you don’t get enough niacin or tryptophan from the foods you eat. Severe niacin deficiency leads to a disease called pellagra. Pellagra, which is uncommon in developed countries, can have these effects:
- Rough skin that turns red or brown in the sun
- A bright red tongue
- Vomiting, constipation, or diarrhea
- Extreme tiredness
- Aggressive, paranoid, or suicidal behavior
- Hallucinations, apathy, loss of memory
In its final stages, pellagra leads to loss of appetite followed by death.
What are some effects of niacin on health?
Scientists are studying niacin to better understand how it affects health. Here is an example of what this research has shown.
Scientists have studied the use of large doses of niacin in the form of nicotinic acid to help reduce the risk of heart attack and stroke in people with atherosclerosis. They found that prescription-strength nicotinic acid (more than 100 times the recommended dietary allowance) can lower blood levels of LDL (bad) cholesterol, raise levels of HDL (good) cholesterol, and lower levels of triglycerides. But these favorable effects on blood lipids (fats) don’t affect the risk of having a cardiovascular event, such as heart attack, sudden cardiac death, or stroke. In addition, experts do not recommend high doses of nicotinic acid for people taking a statin medication.
Your healthcare provider should approve and supervise any use of very high doses of nicotinic acid (in the thousands of milligrams) to treat atherosclerosis.
Can niacin be harmful?
The niacin that food naturally contains is safe. However, dietary supplements with 30 mg or more of nicotinic acid can make the skin on your face, arms, and chest turn red and burn, tingle, and itch. These symptoms can also lead to headaches, rashes, and dizziness.
If you take nicotinic acid as a medication in doses of 1,000 or more mg/day, it can cause more severe side effects. These include:
- Low blood pressure (which can increase the risk of falls)
- Extreme tiredness
- High blood sugar levels
- Nausea, heartburn, and abdominal pain
- Blurred or impaired vision and fluid buildup in the eyes
Long-term treatment, especially with extended-release forms of nicotinic acid, can cause liver problems, including hepatitis and liver failure.
Niacin in the form of nicotinamide has fewer side effects than nicotinic acid. However, at high doses of 500 mg/day or more, nicotinamide can cause diarrhea, easy bruising, and can increase bleeding from wounds. Even higher doses of 3,000 mg/day or more can cause nausea, vomiting, and liver damage.
What is the vitamin B3 (Niacin) deficiency symptoms and Signs ?
Primary niacin deficiency results from extremely inadequate intake of both niacin and tryptophan, which usually occurs in areas where maize (Indian corn) constitutes a substantial part of the diet. Bound niacin, found in maize, is not assimilated in the gastrointestinal tract unless it has been previously treated with alkali, as when tortillas are prepared. Corn protein is also deficient in tryptophan.
The high incidence of pellagra in India among people who eat millet with a high leucine content has led to the hypothesis that amino acid imbalance may contribute to deficiency. Deficiencies of protein and many B vitamins commonly accompany primary niacin deficiency.
In the past, niacin deficiency was common, especially in the Southern States of the U.S. Now, however, most people get enough vitamin B-3 in their diet.
According to the Office of Dietary Supplements (ODS), a person who lacks vitamin B-3 may experience:
- a pigmented rash on skin that is exposed to the sun
- rough appearance to the skin
- bright red tongue
- fatigue or apathy
- vomiting, constipation, and diarrhea
- circulatory problems
- memory loss
- in severe cases, hallucinations
A severe lack of vitamin B-3 can result in pellagra. The condition can be fatal.
Pellagra affects the skin, nervous system, digestive system, and mucous membranes, such as the eyes and nose.
Symptoms of pellagra include:
- Symmetrical lesions on both sides of the body. The lesions are most visible at pressure points and on areas of the skin exposed to the sun. Some people develop lesions that cover their entire hands or feet.
- Butterfly-shaped lesions on the face, or a “necklace” of lesions around the neck that develop after spending time in the sun.
- Pain, swelling, and irritation of the mouth or other mucous membranes, such as the vagina or the urethra. Severe deficiency can cause the tongue to turn red or swell. Some people develop sores under the tongue or on their lips.
- Pain and burning in the throat, chest, or stomach.
- Digestive pain, such as swelling, vomiting, nausea, diarrhea, and constipation. Some people develop ulcers in their bowels that cause bloody diarrhea.
- Changes in personality and mental health, including losing contact with reality (psychosis), confusion, memory problems, depression, and paranoia. Sometimes, these symptoms may be incorrectly diagnosed as mental illness.
Less severe cases of vitamin B-3 deficiency may cause less serious symptoms in the skin, nervous system, digestive system, or mucous membranes. Those symptoms might include:
- irritated or red skin
- unexplained digestive problems
- mood issues, such as anxiety or depression
- changes in thinking or the ability to concentrate
- poor circulation
Factors that can lead to low levels of B-3 include:
- having a diet low in tryptophans or a condition that reduces the body’s ability to convert tryptophan to niacin, such as Hartnup disease or carcinoid syndrome
- undernutrition, for example, due to alcohol use disorder, anorexia, and inflammatory bowel disease
- a low intake of vitamin B-2, B-6, or iron, as this can reduce the amount of tryptophan that converts to niacin
Niacin Deficiency Causes
In the 1800s, pellagra was common among poor Americans whose diets consisted mostly of corn, molasses, and salt pork — all poor sources of niacin. Today, most people in the developed world get plenty of niacin in their diets. Niacin deficiency is more likely to be caused by problems that affect absorption of niacin or tryptophan. The most common cause is alcoholism. Other possible causes include disorders of the digestive system and prolonged treatment with the tuberculosis drug isoniazid (Laniazid, Nydrazid).
Niacin Deficiency Treatments
The recommended daily allowance (RDA) for niacin is 16 milligrams per day for men and 14 milligrams per day for women. Good sources of niacin include red meat, fish, poultry, fortified breads and cereals, and enriched pasta and peanuts.
Supplements of niacin such as nicotinic acid or nicotinamide are approved by the FDA for treating and preventing niacin deficiency. Under the supervision of a doctor, high doses of over-the-counter or prescription niacin or nicotinic acid can be used to treat high cholesterol, including high triglycerides.
The most common side effect of niacin supplementation is flushing. Other side effects include nausea, vomiting, pruritus, hives, abnormally high liver enzymes, and constipation. However, too much nicotinic acid or niacin can be harmful. Avoid taking more than your doctor prescribes or recommends. If you are taking doses of more than 100 milligrams per day, doctors recommend periodic liver function tests.
If you have a history of gout, you should be careful with how much niacin you consume because it is also known to elevate serum uric acid concentration.
USANA CellSentials™ contain 20mg Vitamin B3
For more information. Please check:
- Penberthy WT, Kirkland JB. Niacin. In: Erdman JW, Macdonald IA, Zeisel SH, eds. Present Knowledge in Nutrition, 10th ed. Washington, DC: Wiley-Blackwell; 2012:293-306.
- Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes: Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press, 1998.
- Kirkland JB. Niacin. In: Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease, 11th ed. Baltimore, MD: Williams & Wilkins; 2014:331-40.
- Bourgeois C, Moss J. Niacin. In: Coates PM, Betz JM, Blackman MR, Cragg GM, Levine M, Moss J, White JD, eds. Encyclopedia of Dietary Supplements, 2nd ed. New York, NY: Informa Healthcare; 2010:562-9.
- Gibson, RS. Principles of Nutritional Assessment, Second Edition. New York: Oxford University Press. Copyright 2005.