Why niacin

This is a fact sheet intended for health professionals. For a reader-friendly overview of Niacin, see our consumer fact sheet on Niacin.

Niacin also known as vitamin B3 is one of the water-soluble B vitamins. Niacin is the generic name for nicotinic acid pyridinecarboxylic acid , nicotinamide niacinamide or pyridinecarboxamide , and related derivatives, such as nicotinamide riboside [ ]. 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 enzymes require NAD to catalyze reactions in the body, which is more than for any other vitamin-derived coenzyme [ 1 ]. NAD is also converted into another active form, the coenzyme nicotinamide adenine dinucleotide phosphate NADP , in all tissues except skeletal muscle [ 4 ].

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 [ 4 ]. 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. The body also converts some tryptophan, an amino acid in protein, to NAD, so tryptophan is considered a dietary source of niacin. Ingested niacin is absorbed primarily in the small intestine, but some is absorbed in the stomach [ ]. 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-methylpyridonecarboxamide, 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-methylpyridonecarboxamide [ 2 ].

Excretion rates in adults of more than An adult has deficient niacin status when urinary-excretion rates are less than 5. Indicators of inadequacy such as this and other biochemical signs e. 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 index" the ratio of erythrocyte NAD to NADP concentrations below 1 suggests that an individual is at risk of developing niacin deficiency [ 8 ]. No functional biochemical tests that reflect total body stores of niacin are available [ 5 ].

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:. 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 months, the AI for niacin is in mg NE and is based on amounts consumed from breast milk and solid foods.

Food Niacin is present in a wide variety of foods. Many animal-based foods—including poultry, beef, and fish—provide about mg niacin per serving, primarily in the highly bioavailable forms of NAD and NADP [ 3 ].

Plant-based foods, such as nuts, legumes, and grains, provide about mg niacin per serving, mainly as nicotinic acid. Many breads, cereals, and infant formulas in the United States and many other countries contain added niacin. Niacin that is added to enriched and fortified foods is in its free form and therefore highly bioavailable [ 2 ]. Tryptophan is another food source of niacin because this amino acid—when present in amounts beyond that required for protein synthesis—can be converted to NAD, mainly in the liver [ 3 , 5 ].

The most commonly used estimate of efficiency for tryptophan conversion to NAD is i. Turkey is an example of a food high in tryptophan; a 3-oz portion of turkey breast meat provides about mg tryptophan, which could be equivalent to 3 mg niacin [ 9 ]. However, the efficiency of the conversion of tryptophan to NAD varies considerably in different people [ 3 ]. They do not include the contribution of tryptophan, some of which is converted to NAD in the body.

The U. Food and Drug Administration FDA developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for niacin is 16 mg for adults and children aged 4 years and older [ 10 ].

The FDA does not require food labels to list niacin content unless niacin has been added to the food. Department of Agriculture's USDA's FoodData Central lists the nutrient content of many foods and provides a comprehensive list of foods containing niacin arranged by nutrient content. Dietary supplements Niacin is available in multivitamin-mineral products, in supplements containing other B-complex vitamins, and in supplements containing niacin only.

Nicotinic acid and nicotinamide are the two most common forms of niacin in supplements. Some niacin-only supplements contain mg or more per serving, which is much higher than the RDA for this nutrient [ 11 ].

Nicotinic acid in supplemental amounts beyond nutritional needs can cause skin flushing, so some formulations are manufactured and labeled as prolonged, sustained, extended, or timed release to minimize this unpleasant side effect.

Nicotinamide does not produce skin flushing because of its slightly different chemical structure [ 2 , 12 ].

Pellagra, which is uncommon in developed countries, can have these effects:. Scientists are studying niacin to better understand how it affects health. Here is an example of what this research has shown. Cardiovascular disease 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 times the recommended dietary allowance can lower blood levels of LDL bad cholesterol, raise levels of HDL good cholesterol, and lower levels of triglycerides. 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. The niacin that food and beverages naturally contain 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.

These include:. 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. The daily upper limits for niacin from dietary supplements are listed below.

Niacin dietary supplements can interact or interfere with certain medicines that you take, and some medicines can lower niacin levels in your body. Here are some examples:. You may opt-out of e-mail communications at any time by clicking on the Unsubscribe link in the e-mail.

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Products and services. Thank you for Subscribing Our Housecall e-newsletter will keep you up-to-date on the latest health information. Please try again. Something went wrong on our side, please try again. All B vitamins help the body convert food carbohydrates into fuel glucose , which the body uses to produce energy. These B vitamins, often referred to as B-complex vitamins, also help the body use fats and protein.

B-complex vitamins are needed for a healthy liver, healthy skin, hair, and eyes, and to help the nervous system function properly. Niacin also helps the body make various sex and stress-related hormones in the adrenal glands and other parts of the body. Niacin helps improve circulation, and it has been shown to suppress inflammation. You can meet all of your body's needs for B3 through diet. It is rare for anyone in the developed world to have a B3 deficiency.

In the U. Severe deficiency can cause a condition known as pellagra. Pellagra is characterized by cracked, scaly skin, dementia, and diarrhea. It is generally treated with a nutritionally balanced diet and niacin supplements.

Niacin deficiency also causes burning in the mouth and a swollen, bright red tongue. Very high doses of B3, available by prescription, have been studied to prevent or improve symptoms of the following conditions. However, at high doses niacin can be toxic. Researchers are trying to determine if inositol hexanicotinate has similar benefits without serious side effects. But results are inconclusive. Niacin, but not niacinamide, has been used since the s to lower elevated LDL bad cholesterol and triglyceride fat levels in the blood.

However, side effects can be unpleasant and even dangerous. High doses of niacin cause:. A time-release form of niacin reduces flushing. But long-term use is associated with liver damage. In addition, niacin can interact with other cholesterol-lowering medicines. You should not take niacin at high doses without your doctor's supervision. In one study, men with existing heart disease slowed down the progression of atherosclerosis by taking niacin along with colestipol.

They experienced fewer heart attacks and deaths, as well. In another study, people with heart disease and high cholesterol who took niacin along with simvastatin Zocor had a lower risk of having a first heart attack or stroke.

Their risk of death was also lower. In another study, men who took niacin alone seemed to reduce the risk of having a second heart attack, although it did not reduce the risk of death. In type 1 diabetes, the body's immune system mistakenly attacks the cells in the pancreas that make insulin, eventually destroying them. Niacinamide may help protect those cells for a time.

More research is needed. Researchers have also looked at whether high-dose niacinamide might reduce the risk of type 1 diabetes in children at risk for the disease. One study found that it did.

But another, larger study found it did not protect against developing type 1 diabetes. The effect of niacin on type 2 diabetes is more complicated. People with type 2 diabetes often have high levels of fats and cholesterol in the blood.

Niacin, often along with other medications, can lower those levels. However, niacin may also raise blood sugar levels, which is particularly dangerous for someone with diabetes.