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.
Available Forms
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.
How to Take It
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)
Precautions
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.
Possible Interactions
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 inc