Vitamin B3 is one of 8 B vitamins. It is also known as niacin (nicotinic acid) and has 2 other forms, niacinamide (nicotinamide) and inositol hexanicotinate, which have different effects from niacin.

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.

All the B vitamins are water-soluble, meaning that the body does not store them.

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.S., alcoholism is the main cause of vitamin B3 deficiency.

Symptoms of mild B3 deficiency include:

• Indigestion
• Fatigue
• Canker sores
• Vomiting
• Poor circulation
• Depression

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. You should not take doses higher than the Recommended Daily Allowance (RDA) except under your doctor's supervision. Researchers are trying to determine if inositol hexanicotinate has similar benefits without serious side effects. But results are inconclusive.

High cholesterol

Niacin, but not niacinamide, has been used since the 1950s 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:

• Flushing of the skin
• Stomach upset (which usually subsides within a few weeks)
• Headache
• Dizziness
• Blurred vision
• An increased risk of liver damage

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.

Atherosclerosis and heart disease

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.

Diabetes

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. More research is needed.

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. For that reason, if you have diabetes, you should take niacin only under the direction of your doctor, and you should be carefully monitored for high blood sugar.

Osteoarthritis

One preliminary study suggested that niacinamide may improve arthritis symptoms, including increasing joint mobility and reducing the amount of non-steroidal anti-inflammatory drugs (NSAIDs) needed. More research is needed.

Other

Alzheimer disease: Population studies show that people who get higher levels of niacin in their diet have a lower risk of Alzheimer disease. No studies have evaluated niacin supplements, however.

Cataracts: One large population study found that people who got a lot of niacin in their diets had a lower risk of developing cataracts.

Skin conditions: Researchers are studying topical forms of niacin as treatments for rosacea, aging, and prevention of skin cancer, although it is too early to know whether it is effective.

Although there is no evidence that it helps treat any of these conditions, researchers are also studying the use of vitamin B3 in treating:

• ADHD
• Migraines
• Dizziness
• Depression
• Motion sickness
• Alcohol dependence

The best food sources of vitamin B3 are:

• Beets
• Brewer's yeast
• Beef liver
• Beef kidney
• Fish
• Salmon
• Swordfish
• Tuna
• Sunflower seeds
• Peanuts

Bread and cereals are usually fortified with niacin. In addition, foods that contain tryptophan, an amino acid the body coverts into niacin, include poultry, red meat, eggs, and dairy products.

Vitamin B3 is available in several different supplement forms:

• Niacinamide
• Niacin
• Inositol hexaniacinate.

Niacin is available as a tablet or capsule in both regular and timed-release forms. The timed-release tablets and capsules may have fewer side effects than regular niacin. However, the timed-release versions are more likely to cause liver damage. Regardless of which form of niacin you are using, doctors recommend periodic liver function tests when using high doses (above 100 mg per day) of niacin.

Generally, high doses of niacin are used to control specific diseases. Such high doses must be prescribed by a doctor who will increase the amount of niacin slowly, over the course of 4 to 6 weeks. Take niacin with meals to avoid stomach irritation.

Daily recommendations for niacin in the diet of healthy individuals are:

Pediatric

• Infants, birth to 6 months: 2 mg (adequate intake)
• Infants, 7 months to 1 year: 4 mg (adequate intake)
• Children, 1 to 3 years: 6 mg (RDA)
• Children, 4 to 8 years: 8 mg (RDA)
• Children, 9 to 13 years: 12 mg (RDA)
• Boys, 14 to 18 years: 16 mg (RDA)
• Girls, 14 to 18 years: 14 mg (RDA)

Adult

• Men, 19 years and older: 16 mg (RDA)
• Women, 19 years and older: 14 mg (RDA)
• Pregnant women: 18 mg (RDA)
• Breastfeeding women: 17 mg (RDA)

Because of the potential for side effects and interactions with medications, you should take dietary supplements only under the supervision of a knowledgeable health care provider. Side effects may include diarrhea, headache, stomach discomfort, and bloating.

High doses (50 mg or more) of niacin can cause side effects. The most common side effect is called "niacin flush," which is a burning, tingling sensation in the face and chest, and red or flushed skin. Taking an aspirin 30 minutes prior to the niacin may help reduce this symptom.

At very high doses, used to lower cholesterol and treat other conditions, liver damage and stomach ulcers can occur. Your doctor will regularly check your liver function through a blood test.

People with a history of liver disease, kidney disease, or stomach ulcers should not take niacin supplements. Those with diabetes or gallbladder disease should do so only under the close supervision of their doctors.

Stop taking niacin or niacinamide at least 2 weeks before a scheduled surgery.

Niacin and niacinamide may make allergies worse by increasing histamine.

People with low blood pressure should not take niacin or niacinamide because they may cause a dangerous drop in blood pressure. DO NOT take niacin if you have a history of gout.

People with coronary artery disease or unstable angina should not take niacin without their doctor's supervision, as large doses can raise the risk of heart rhythm problems.

Taking any one of the B vitamins for a long period of time can result in an imbalance of other important B vitamins. For this reason, you may want to take a B-complex vitamin, which includes all the B vitamins.

Because of its impact on the liver, vitamin B3 can interact with several medications. If you are currently taking medications, or regularly drink alcohol, you should not use niacin without talking to your health care provider first. Below is a partial list of medications that may interact with vitamin B3.

Antibiotics, tetracycline: Niacin should not be taken at the same time as the antibiotic tetracycline because it interferes with the absorption and effectiveness of this medication. All vitamin B complex supplements act in this way and should be taken at different times from tetracycline.

Aspirin: Taking aspirin before taking niacin may reduce flushing from niacin. But take it only under your doctor's supervision.

Anti-seizure medications: Phenytoin (Dilantin) and valproic acid (Depakote) may cause niacin deficiency in some people. Taking niacin with carbamazepine (Tegretol) or mysoline (Primidone) may increase levels of these medications in the body.

Anticoagulants (blood thinners): Niacin may make the effects of these medications stronger, increasing the risk of bleeding.

Blood pressure medications, alpha-blockers: Niacin can make the effects of medications taken to lower blood pressure stronger, leading to the risk of low blood pressure.

Cholesterol-lowering medications: Niacin binds the cholesterol-lowering medications known as bile-acid sequestrants and may make them less effective. For this reason, niacin and these medications should be taken at different times of the day. Bile-acid sequestrants include colestipol (Colestid), colesevelam (Welchol), and cholestyramine (Questran).

Statins: Some scientific evidence suggests that taking niacin with simvastatin (Zocor) appears to slow the progression of heart disease. However, the combination may also increase the likelihood for serious side effects, such as muscle inflammation or liver damage.

Diabetes medications: Niacin may increase blood sugar levels. People taking insulin, metformin (Glucophage), glyburide (Dibeta, Micronase), glipizide (Glucotrol), or other medications used to treat high blood glucose levels should monitor their blood sugar levels closely when taking niacin supplements.

Isoniazid (INH): INH, a medication used to treat tuberculosis, may cause a niacin deficiency.

Nicotine patches: Using nicotine patches with niacin may worsen or increase the risk of flushing associated with niacin.

These medications may lower levels of niacin in the body:

• Azathioprine (Imuran)
• Chloramphenicol (Chloromycetin)
• Cycloserine (Seromycin)
• Fluorouracil
• Levodopa and carbidopa
• Mercaptopurine (Purinethol)

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