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 to convert food (carbohydrates) into fuel (glucose), which is "burned" to produce energy. These B vitamins, often referred to as B complex vitamins, also help the body metabolize fats and protein. B complex vitamins are necessary for healthy skin, hair, eyes, and liver. They also 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 is effective in improving circulation and reducing cholesterol levels in the blood.

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 United States, alcoholism is the prime cause of vitamin B3 deficiency.

Symptoms of mild deficiency include indigestion, fatigue, canker sores, vomiting, and 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 results in burning in the mouth and a swollen, bright red tongue.

Very high doses of B3 (available by prescription) have been shown to prevent or improve symptoms of the following conditions. However, taken at high doses niacin can be toxic, so you should take doses higher than the Recommended Daily Allowance only under your doctor's supervision. Researchers are trying to determine if inositol hexanicotinate has similar benefits without serious side effects, but so far results are preliminary.

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 and is more effective in increasing HDL ("good") cholesterol levels than other cholesterol-lowering medications. However, side effects can be unpleasant and even dangerous. High doses of niacin cause flushing of the skin (which can be reduced by taking aspirin 30 minutes before the niacin), stomach upset (which usually subsides within a few weeks), headache, dizziness, and blurred vision. There is an increased risk of liver damage. A time-release form of niacin reduces flushing, but its long-term use is associated with liver damage. In addition, niacin can interact with other cholesterol-lowering drugs (see "Possible Interactions"). You should not take niacin at high doses without your doctor's supervision.

Atherosclerosis

Because niacin lowers LDL and triglycerides in the blood, it may help prevent atherosclerosis (hardening of the arteries) and is sometimes prescribed along with other medications. However, niacin also increases levels of homocysteine levels in the blood, which is associated with an increased risk of heart disease. This is another reason you should not take high doses of niacin without your doctor's supervision.

Diabetes

Some evidence suggests that niacinamide (but not niacin) might help delay the onset of insulin dependence (in other words, delay the time that you would need to take insulin) in type 1 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, but more research is needed to tell for sure.

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, and niacin, often in conjunction with other drugs, can lower those levels. However, niacin can also raise blood sugar levels, resulting in hyperglycemia, which is particularly dangerous for someone with diabetes. For that reason, anyone with diabetes should take niacin only when directed to do so by their doctor, and should be carefully monitored for hyperglycemia.

Osteoarthritis

One preliminary study suggested that niacinamide may improve arthritis symptoms, including increasing joint mobility and reducing the amount of nonsteroidal anti-inflammatory drugs (NSAIDs) needed. More research is needed to determine whether there is any real benefit.

Other

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

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

The best dietary sources of vitamin B3 are found in beets, brewer's yeast, beef liver, beef kidney, fish, salmon, swordfish, tuna, sunflower seeds, and 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, and 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're using, doctors recommend periodic liver function tests when using high doses (above 100 mg per day) of niacin.

Daily recommendations for niacin in the diet of healthy individuals are listed below.

Generally, high doses of niacin are used to control specific diseases, such as high cholesterol. Such high doses are considered "pharmacologic" and must be prescribed by a doctor, who will have you increase the amount of niacin slowly, over the course of 4 - 6 weeks, and take the medicine with meals to avoid stomach irritation.

Pediatric

• Infants birth - 6 months: 2 mg (adequate intake)
• Infants 7 months - 1 year: 4 mg (adequate intake)
• Children 1- 3 years: 6 mg (RDA)
• Children 4 - 8 years: 8 mg (RDA)
• Children 9 - 13 years: 12 mg (RDA)
• Males 14 - 18 years: 16 mg (RDA)
• Females 14 - 18 years: 14 mg (RDA)

Adult

• Males 19 years and older: 16 mg (RDA)
• Females 19 years and older: 14 mg (RDA)
• Pregnant females: 18 mg (RDA)
• Breastfeeding females: 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.

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 the very high doses used to lower cholesterol and treat other conditions, liver damage and stomach ulcers can occur. Your health care provider will periodically check your liver function through a blood test.

People with a history of liver 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 doctor.

Niacin should not be used if you have gout.

Taking any one of the B complex vitamins for a long period of time can result in an imbalance of other important B vitamins. For this reason, it is generally important to take a B complex vitamin with any single B vitamin.

If you are currently taking any of the following medications, you should not use niacin without first talking to your health care provider.

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 therefore be taken at different times from tetracycline.)

Aspirin -- Taking aspirin before taking niacin may reduce flushing associated with this vitamin, but should only be done under your doctor's supervision.

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 bile-acid sequestrants (cholesterol-lowering medications such as colestipol, colesevelam, and cholestyramine) and may decrease their effectiveness. For this reason, niacin and these medications should be taken at different times of the day.

Recent scientific evidence suggests that taking niacin with simvastatin (a drug that belongs to a class of cholesterol-lowering medications known as HMG-CoA reductase inhibitors, or statins), appears to slow down 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 glucose (sugar) levels. People taking insulin, metformin, glyburide, glipizide, or other medications used to treat high blood sugar levels should monitor their blood sugar levels closely when taking niacin supplements.

Isoniazid (INH) -- INH, a medication used to treat tuberculosis, may lower levels of niacin in the body and cause a deficiency.

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

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