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Riboflavin (also known as vitamin B2) is one of the B vitamins, which are all water soluble. Riboflavin is naturally present in some foods, added to some food products, and available as a dietary supplement. This vitamin is an essential component of two major coenzymes, flavin mononucleotide (FMN; also known as riboflavin-5’-phosphate) and flavin adenine dinucleotide (FAD). These coenzymes play major roles in energy production; cellular function, growth, and development; and metabolism of fats, drugs, and steroids. The conversion of the amino acid tryptophan to niacin (sometimes referred to as vitamin B3) requires FAD. Similarly, the conversion of vitamin B6 to the coenzyme pyridoxal 5’-phosphate needs FMN. In addition, riboflavin helps maintain normal levels of homocysteine, an amino acid in the blood.
More than 90% of dietary riboflavin is in the form of FAD or FMN; the remaining 10% is comprised of the free form and glycosides or esters. Most riboflavin is absorbed in the proximal small intestine. The body absorbs little riboflavin from single doses beyond 27 mg and stores only small amounts of riboflavin in the liver, heart, and kidneys. When excess amounts are consumed, they are either not absorbed or the small amount that is absorbed is excreted in urine.
Bacteria in the large intestine produce free riboflavin that can be absorbed by the large intestine in amounts that depend on the diet. More riboflavin is produced after ingestion of vegetable-based than meat-based foods.
Riboflavin is yellow and naturally fluorescent when exposed to ultraviolet light. Moreover, ultraviolet and visible light can rapidly inactivate riboflavin and its derivatives. Because of this sensitivity, lengthy light therapy to treat jaundice in newborns or skin disorders can lead to riboflavin deficiency. The risk of riboflavin loss from exposure to light is the reason why milk is not typically stored in glass containers.
Riboflavin status is not routinely measured in healthy people. A stable and sensitive measure of riboflavin deficiency is the erythrocyte glutathione reductase activity coefficient (EGRAC), which is based on the ratio between this enzyme’s in vitro activity in the presence of FAD to that without added FAD. The most appropriate EGRAC thresholds for indicating normal or abnormal riboflavin status are uncertain. An EGRAC of 1.2 or less is usually used to indicate adequate riboflavin status, 1.2–1.4 to indicate marginal deficiency, and greater than 1.4 to indicate riboflavin deficiency. However, a higher EGRAC does not necessarily correlate with degree of riboflavin deficiency. Furthermore, the EGRAC cannot be used in people with glucose-6-phosphate dehydrogenase deficiency, which is present in about 10% of African Americans.
Another widely used measure of riboflavin status is fluorometric measurement of urinary excretion over 24 hours (expressed as total amount of riboflavin excreted or in relation to the amount of creatinine excreted). Because the body can store only small amounts of riboflavin, urinary excretion reflects dietary intake until tissues are saturated. Total riboflavin excretion in healthy, riboflavin-replete adults is at least 120 mcg/day; a rate of less than 40 mcg/day indicates deficiency. This technique is less accurate for reflecting long-term riboflavin status than EGRAC. Also, urinary excretion levels can decrease with age and increase with exposure to stress and certain drugs, and the amount excreted strongly reflects recent intake.
Recommended Intakes
Intake recommendations for riboflavin and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies. DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and sex, include:
- Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals.
- Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA.
- Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals; usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them; can also be used to assess the nutrient intakes of individuals.
- Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.
Table 1 lists the current RDAs for riboflavin. For infants from birth to 12 months, the FNB established an AI for riboflavin that is equivalent to the mean intake of riboflavin in healthy, breastfed infants.
Table 1: Recommended Dietary Allowances for Riboflavin
Age |
Male |
Female |
Pregnancy |
Lactation |
Birth to 6 months* |
0.3 mg |
0.3 mg |
|
|
7–12 months* |
0.4 mg |
0.4 mg |
|
|
1–3 years |
0.5 mg |
0.5 mg |
|
|
4–8 years |
0.6 mg |
0.6 mg |
|
|
9–13 years |
0.9 mg |
0.9 mg |
|
|
14–18 years |
1.3 mg |
1.0 mg |
1.4 mg |
1.6 mg |
19-50 years |
1.3 mg |
1.1 mg |
1.4 mg |
1.6 mg |
51+ years |
1.3 mg |
1.1 mg |
|
|
Sources of Riboflavin
Food
Foods that are particularly rich in riboflavin include eggs, organ meats (kidneys and liver), lean meats, and milk. Green vegetables also contain riboflavin. Grains and cereals are fortified with riboflavin in the United States and many other countries. The largest dietary contributors of total riboflavin intake in U.S. men and women are milk and milk drinks, bread and bread products, mixed foods whose main ingredient is meat, ready-to-eat cereals, and mixed foods whose main ingredient is grain. The riboflavin in most foods is in the form of FAD, although the main form in eggs and milk is free riboflavin.
About 95% of riboflavin in the form of FAD or FMN from food is bioavailable up to a maximum of about 27 mg of riboflavin per meal or dose. The bioavailability of free riboflavin is similar to that of FAD and FMN. Because riboflavin is soluble in water, about twice as much riboflavin content is lost in cooking water when foods are boiled as when they are prepared in other ways, such as by steaming or microwaving.
Dietary supplements
Riboflavin is available in many dietary supplements. Multivitamin/multimineral supplements with riboflavin commonly provide 1.3 mg riboflavin (100% of the DV). Supplements containing riboflavin only or B-complex vitamins (that include riboflavin) are also available. In most supplements, riboflavin is in the free form, but some supplements have riboflavin 5’-phosphate.
Riboflavin Intakes and Status
Most people in the United States consume the recommended amounts of riboflavin. An analysis of data from the 2003-2006 National Health and Nutrition Examination Survey (NHANES) showed that less than 6% of the U.S. population has an intake of riboflavin from foods and supplements below the EAR. An analysis of self-reported data from the 1999–2004 NHANES found that intakes of riboflavin were higher in lacto-ovo vegetarians (2.3 mg/day) than nonvegetarians (2.1 mg/day).
Among children and teens, the average daily riboflavin intake from foods is 1.8 mg for ages 2–5 years, 1.9 mg for ages 6–11, and 2.1 mg for ages 12–19. In adults, the average daily riboflavin intake from foods is 2.5 mg in men and 1.8 mg in women. The average daily riboflavin intake from foods and supplements in children and teens is 2.1 mg for ages 2–5 years, 2.2 mg for ages 6–11, and 2.3 mg for ages 12–19. In adults aged 20 and older, the average daily riboflavin intake from foods and supplements is 4.5 mg in men and 4.7 mg in women.
Riboflavin Deficiency
Riboflavin deficiency is extremely rare in the United States. In addition to inadequate intake, causes of riboflavin deficiency can include endocrine abnormalities (such as thyroid hormone insufficiency) and some diseases. The signs and symptoms of riboflavin deficiency (also known as ariboflavinosis) include skin disorders, hyperemia (excess blood) and edema of the mouth and throat, angular stomatitis (lesions at the corners of the mouth), cheilosis (swollen, cracked lips), hair loss, reproductive problems, sore throat, itchy and red eyes, and degeneration of the liver and nervous system. People with riboflavin deficiency typically have deficiencies of other nutrients, so some of these signs and symptoms might reflect these other deficiencies. Severe riboflavin deficiency can impair the metabolism of other nutrients, especially other B vitamins, through diminished levels of flavin coenzymes. Anemia and cataracts can develop if riboflavin deficiency is severe and prolonged.
The earlier changes associated with riboflavin deficiency are easily reversed. However, riboflavin supplements rarely reverse later anatomical changes (such as formation of cataracts).
Groups at Risk of Riboflavin Inadequacy
The following groups are among those most likely to have inadequate riboflavin status.
Vegetarian athletes
Exercise produces stress in the metabolic pathways that use riboflavin. The Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine state that vegetarian athletes are at risk of riboflavin deficiency because of their increased need for this nutrient and because some vegetarians exclude all animal products (including milk, yogurt, cheese, and eggs), which tend to be good sources of riboflavin, from their diets. These associations recommend that vegetarian athletes consult a sports dietitian to avoid this potential problem.
Pregnant and lactating women and their infants
Pregnant or lactating women who rarely consume meats or dairy products (such as those living in developing countries and some vegetarians in the United States) are at risk of riboflavin deficiency, which can have adverse effects on the health of both mothers and their infants. Riboflavin deficiency during pregnancy, for example, can increase the risk of preeclampsia. The limited evidence on the benefits of riboflavin supplements during pregnancy in both developed and developing countries is mixed.
Riboflavin intakes during pregnancy have a positive association with infant birth weight and length. Infants of mothers with riboflavin deficiency or low dietary intakes (less than 1.2 mg/day) during pregnancy have a higher risk of deficiency and of certain birth defects (such as outflow tract defects of the heart). However, maternal riboflavin intake has no association with the risk of orofacial clefts in infants.
In well-nourished women, riboflavin concentrations in breast milk range from 180 to 800 mcg/L and concentrations of riboflavin in breast milk increase over time. In developing countries, in contrast, riboflavin levels in breast milk range from 160 to 220 mcg/L.
People who are vegan and/or consume little milk
In people who eat meat and dairy products, these foods contribute a substantial proportion of riboflavin in the diet. For this reason, people who live in developing countries and have limited intakes of meat and dairy products have an increased risk of riboflavin deficiency. Vegans and those who consume little milk in developed countries are also at risk of riboflavin inadequacy.
People with infantile Brown-Vialetto-Van Laere syndrome
Infantile Brown-Vialetto-Van Laere syndrome is a very rare neurological disorder that can begin at any age and is associated with deafness, bulbar palsy (a motor-neuron disease), and respiratory difficulties. The disease is caused by mutations in the SLC52A3 gene, which encodes the intestinal riboflavin transporter. As a result, these patients have riboflavin deficiency. Riboflavin supplementation can be a life-saving treatment in this population.
Riboflavin and Health
Migraine headaches
Migraine headaches typically produce intense pulsing or throbbing pain in one area of the head. These headaches are sometimes preceded or accompanied by aura (transient focal neurological symptoms before or during the headaches). Mitochondrial dysfunction is thought to play a causal role in some types of migraine. Because riboflavin is required for mitochondrial function, researchers are studying the potential use of riboflavin to prevent or treat migraine headaches.
Some, but not all, of the few small studies conducted to date have found evidence of a beneficial effect of riboflavin supplements on migraine headaches in adults and children. In a randomized trial in 55 adults with migraine, 400 mg/day riboflavin reduced the frequency of migraine attacks by two per month compared to placebo. In a retrospective study in 41 children (mean age 13 years) in Italy, 200 or 400 mg/day riboflavin for 3 to 6 months significantly reduced the frequency (from 21.7 ± 13.7 to 13.2 ± 11.8 migraine attacks over a 3-month period) and intensity of migraine headaches during treatment. The beneficial effects lasted throughout the 1.5-year follow-up period after treatment ended. However, two small randomized studies in children found that 50 to 200 mg/day riboflavin did not reduce the number of migraine headaches or headache severity compared to placebo.
The Quality Standards Subcommittee of the American Academy of Neurology and the American Headache Society concluded that riboflavin is probably effective for preventing migraine headaches and recommended offering it for this purpose. The Canadian Headache Society recommends 400 mg/day riboflavin for migraine headache prevention, noting that although the evidence supporting this recommendation is of low quality, there is some evidence for benefit and side effects (such as discolored urine) are minimal.
Cancer prevention
Experts have theorized that riboflavin might help prevent the DNA damage caused by many carcinogens by acting as a coenzyme with several different cytochrome P450 enzymes. However, data on the relationship between riboflavin and cancer prevention or treatment are limited and study findings are mixed.
A few large observational studies have produced conflicting results on the relationship between riboflavin intakes and lung cancer risk. A prospective study followed 41,514 current, former, and never smokers in the Melbourne Collaborative Cohort Study for 15 years, on average. The average riboflavin intake among all participants was 2.5 mg/day. The results showed a significant inverse association between dietary riboflavin intake and lung cancer risk in current smokers (fifth versus first quintile) but not former or never smokers. However, another cohort study in 385,747 current, former, and never smokers who were followed for up to 12 years in the European Prospective Investigation into Cancer and Nutrition found no association between riboflavin intakes and colorectal cancer risk in any of the three groups. Moreover, the prospective Canadian National Breast Screening Study showed no association between dietary intakes or serum levels of riboflavin and lung cancer risk in 89,835 women aged 40-59 from the general population over 16.3 years, on average.
Observational studies on the relationship between riboflavin intakes and colorectal cancer risk have not yielded conclusive results either. An analysis of data on 88,045 postmenopausal women in the Women’s Health Initiative Observational Study showed that total intakes of riboflavin from both foods and supplements were associated with a lower risk of colorectal cancer. A study that followed 2,349 individuals with cancer and 4,168 individuals without cancer participating in the Netherlands Cohort Study on Diet and Cancer for 13 years found no significant association between riboflavin and proximal colon cancer risk among women.
Future studies, including clinical trials, are needed to clarify the relationship between riboflavin intakes and various types of cancer and determine whether riboflavin supplements might reduce cancer risk.