Vitamin B3 is integral to cell metabolism, particularly in reactions involving the production and use of energy. It occurs in two forms: niacin and nicotinamide. Foods that contain B3 include milk, fish, eggs, green vegetables and yeast. Adverse effects of niacin occur at recommended doses but are less severe than at higher doses. Dosages greater than 3,000 mg per day cause severe toxicity that affects multiple systems in the body.
Benefits
Niacin and nicotinamide treat a variety of disorders including migraine, dizziness and cholera-associated diarrhea. The U.S. Food and Drug Administration has approved niacin to treat high cholesterol and pellagra, or niacin deficiency. Drug stores sell niacin over the counter at a dose of 250 mg. Treating high cholesterol requires a prescription-strength dosage.
Common Effects
Flushing, the most common reaction associated with niacin use, represents the collective dilation of collections of blood vessels in the face, arms and chest that allows increased blood flow to the skin.
Itching occurs because of increased histamine release in the body. Histamine is the same chemical associated with seasonal allergies.
Vitamin B3-related dizziness results when excessive blood vessel dilation leads to a drop in blood pressure and a subsequent decrease in blood flow to the brain.
The histamine response to taking niacin may cause upset stomach. Histamine causes increased acid production in the stomach.
Serious Effects
Liver damage, or hepatotoxicity, commonly occurs at high doses because of the liver's role in detoxification. Too much niacin can overwhelm the liver. A lab test showing elevation of liver enzymes confirms liver toxicity.
Markedly increased acid production in the stomach may increase an individual's risk of developing ulcers.
Visual changes range from blurriness to a total loss of sight.
Increased blood sugar, termed hyperglycemia, may affect kidney function. Niacin itself may affect the kidneys, slowing the excretion of uric acid, which increases the risk of gout.
Interference With Medications
Individuals who take anti-hypertensives, anti-cholesterol medications and anti-gout medications may experience a reduction in effectiveness if they take niacin. These individuals require the supervision of a health care provider if they want to add supplemental vitamin B3.
Warnings
The U.S. National Library of Medicine recommends that individuals who use centrally acting antihypertensives such as clonidine exercise caution when taking niacin because it can cause an unsafe drop in blood pressure.
Alcohol use can worsen the flushing and itchiness associated with the use of niacin.
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