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Riboflavin (vitamin B2)

What is It?

Riboflavin is a water-soluble vitamin which is also known as vitamin B-2 or vitamin G. Riboflavin plays a key role in the metabolism of carbohydrates, fats, and proteins in the body. In the body, riboflavin is converted into flavin mononucleotide (FMN), which is then converted to the coenzyme, flavin adenine dinucleotide (FAD). As part of the electron transport chain in the mitochondria, FAD is central to each cell’s energy production. These two flavoproteins and other enzymes that rely on them are also involved in the metabolism of several other vitamins.

Because of riboflavin’s important roles, deficiency of this vitamin can affect many enzyme systems. Riboflavin deficiency, or ariboflavinosis, shows up as sore throat, redness and swelling of the lining of the mouth and throat, cracks or sores on the outsides of the lips and at the corners of the mouth, anemia, seborrheic dermatitis, and formation of blood vessels in the cornea that interfere with vision.

Risk factors for riboflavin deficiency include excess alcohol consumption, hypothyroidism, adrenal insufficiency, anorexia, lactose intolerance, and light therapy of newborns to treat jaundice.

Taking less than 0.5 to 0.6 milligrams of riboflavin daily can lead to signs of riboflavin deficiency, but more than 25 milligrams of riboflavin daily will probably not be absorbed. The recommended dietary allowance of riboflavin to prevent deficiency ranges from 0.3 mg daily for infants to 1.3 mg daily for adult men. Pregnant women and nursing mothers require slightly more.

Good sources of riboflavin include wheat flour and bread (which have been enriched with riboflavin and other nutrients since 1943 in the U.S.), dairy products, eggs, nuts, green vegetables, and meat.

Riboflavin deficiency can be detected by measuring red blood cell levels of glutathione reductase, an antioxidant enzyme that depends on FAD.

Health Benefits

Riboflavin has a clear role in the prevention and treatment of riboflavin deficiency. Over the years, the use of riboflavin has been suggested for a long list of other reasons, including the prevention of migraine headache, cataracts, and cervical cancer; the treatment of muscle cramps, eye fatigue, carpal tunnel syndrome, glaucoma, acne, and lactic acidosis in patients using anti-HIV drugs; and the promotion of healthy reproductive function and athletic performance. Few of these indications, however, have been studied carefully.

Riboflavin may play a role in preventing migraine headaches. A recent open study showed that 400 mg riboflavin daily could cut the number of migraine headaches a month in half, but the total hours of headache and the intensity of the headaches did not change significantly. An earlier randomized controlled study showed that 3 months of riboflavin 400 mg daily could reduce migraine attack frequency and number of headache days. The researchers in the second study subsequently showed that the mechanism of action of riboflavin differed from that of beta-blockers, another preventive treatment for migraines.

The results have been less clear in the use of riboflavin for preventing cataracts, the leading cause of visual disability in the U.S. and other developed countries. One study looked at riboflavin use and the risk of age-related cataracts, concluding that individuals who consumed the most riboflavin (1.6 to 2.2 mg daily) were about half as likely to develop cataracts as individuals who consumed the least riboflavin (0.08 mg daily). Another study, though, failed to show a difference, though the difference between high riboflavin consumers and low riboflavin consumers was much smaller (1.5 mg/day versus 1.2 mg/day).

Preliminary clinical evidence suggested that riboflavin might be useful in treating lactic acidosis associated with nucleoside-analog treatment of HIV infection, but there have not been careful clinical trials. Similarly, one survey suggested that women who consumed more foods high in riboflavin were less likely to develop precancerous lesions of the cervix, but formal studies have not been reported.


  • tablet
  • capsule

Riboflavin is often combined with other vitamins in a multivitamin or with other B vitamins in a B complex.

Dosage Information

  • For migraine prevention: take 400 mg riboflavin daily. This was the dose in the clinical studies, but other evidence suggests that only 25 mg riboflavin can be absorbed daily. It may take 3 months for maximum benefits.
  • For cataract prevention: take riboflavin 3 mg daily. One study suggests that adding niacin 40 mg daily can contribute to the preventive effects.

Be sure to check out our Dosage Recommendations Chart for riboflavin, which lists therapeutic dosages for specific ailments at a glance.

Guidelines for Use

  • Some experts recommend regularly consuming a diet with foods high in riboflavin as an alternative to taking supplements.
  • For migraine headache prevention, regular use of riboflavin for 3 months may be required before realizing the maximum benefits.

General Interaction

  • Riboflavin absorption can be reduced when it is taken along with blond psyllium, anticholinergic drugs like propantheline (Pro-Banthine), and oral contraceptives.
  • Phenobarbital (and possibly other drugs) can increase the breakdown of riboflavin in the liver.
  • Several drugs (chlorpromazine, doxorubicin, tricyclic antidepressants, quinacrine, and oral contraceptives) can interfere with the conversion of riboflavin to its active form (FAD).
  • Riboflavin can also interact with several lab tests, partly directly and partly because of its discoloration of the urine. Large doses of riboflavin (200 mg twice daily) can cause errors in some urine tests for drugs of abuse.

Possible Side Effects

  • Riboflavin can cause a yellow discoloration of the urine, although this discoloration does not seem to be harmful.
  • High daily doses of riboflavin (400 mg) can cause diarrhea and excess urination.


  • Riboflavin can cause a yellow discoloration of the urine, although this discoloration does not seem to be harmful.
  • High daily doses of riboflavin (400 mg) can cause diarrhea and excess urination.


Cataracts – 25 mg a day

Migraine – 400 mg every morning

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