Riboflavin
Riboflavin, also known as vitamin B2, is a vitamin found in food and used as a dietary supplement. It is required by the body for cellular respiration.
Food sources include eggs, green vegetables, milk and other dairy product, meat, mushrooms, and almonds. Some countries require its addition to grains.
As a supplement it is used to prevent and treat riboflavin deficiency. At amounts far in excess of what is needed to meet dietary needs as a nutrient, riboflavin may prevent migraines. Riboflavin may be given by mouth or injection. It is nearly always well tolerated. Normal doses are safe during pregnancy. Riboflavin was discovered in 1920, isolated in 1933, and first synthesized in 1935.
Definition
Riboflavin, also known as vitamin B2, is a vitamin found in food, sold as a dietary supplement, and used in food fortification programs in countries where deficiency is common.Deficiency
Signs and symptoms
Mild deficiencies can exceed 50% of the population in Third World countries and in refugee situations. Deficiency is uncommon in the United States and in other countries that have wheat flour, bread, pasta, corn meal or rice enrichment regulations. In the U.S., starting in the 1940s, flour, corn meal and rice have been fortified with B vitamins as a means of restoring some of what is lost in milling, bleaching and other processing. For adults 20 and older, average intake from food and beverages is 1.8 mg/day for women and 2.5 mg/day for men. An estimated 23% consume a riboflavin-containing dietary supplement that provides on average 10 mg. The U.S. Department of Health and Human Services conducts National Health and Nutrition Examination Survey every two years and reports food results in a series of reports referred to as "What We Eat In America." From NHANES 2011–2012, estimates were that 8% of women and 3% of men consumed less than the RDA. When compared to the lower Estimated Average Requirements, fewer than 3% did not achieve the EAR level.Riboflavin deficiency results in stomatitis including painful red tongue with sore throat, chapped and fissured lips, and inflammation of the corners of the mouth. There can be oily scaly skin rashes on the scrotum, vulva, philtrum of the lip, or the nasolabial folds. The eyes can become itchy, watery, bloodshot and sensitive to light. Due to interference with iron absorption, even mild to moderate riboflavin deficiency results in an anemia with normal cell size and normal hemoglobin content. This is distinct from anemia caused by deficiency of folic acid or cyanocobalamin, which causes anemia with large blood cells. Deficiency of riboflavin during pregnancy can result in birth defects including congenital heart defects and limb deformities. Prolonged riboflavin insufficiency is also known to cause degeneration of the liver and nervous system.
The stomatitis symptoms are similar to those seen in pellagra, which is caused by niacin deficiency. Therefore, riboflavin deficiency is sometimes called "pellagra sine pellagra", because it causes stomatitis but not widespread peripheral skin lesions characteristic of niacin deficiency.
Riboflavin deficiency prolongs recovery from malaria, despite preventing growth of plasmodium.
Causes
Riboflavin is continuously excreted in the urine of healthy individuals, making deficiency relatively common when dietary intake is insufficient. Riboflavin deficiency is usually found together with other nutrient deficiencies, particularly of other water-soluble vitamins.A deficiency of riboflavin can be primary – poor vitamin sources in one's daily diet – or secondary, which may be a result of conditions that affect absorption in the intestine, the body not being able to use the vitamin, or an increase in the excretion of the vitamin from the body.
Subclinical deficiency has also been observed in women taking oral contraceptives, in the elderly, in people with eating disorders, chronic alcoholism and in diseases such as HIV, inflammatory bowel disease, diabetes and chronic heart disease. The Celiac Disease Foundation points out that a gluten-free diet may be low in riboflavin as enriched wheat flour and wheat foods is a major dietary contribution to total riboflavin intake.
Diagnosis
Overt clinical signs are rarely seen among inhabitants of the developed countries. The assessment of riboflavin status is essential for confirming cases with unspecific symptoms where deficiency is suspected.- Glutathione reductase is a nicotinamide adenine dinucleotide phosphate and FAD-dependent enzyme, and the major flavoprotein in erythrocytes. The measurement of the activity coefficient of erythrocyte glutathione reductase is the preferred method for assessing riboflavin status. It provides a measure of tissue saturation and long-term riboflavin status. In vitro enzyme activity in terms of activity coefficients is determined both with and without the addition of FAD to the medium. ACs represent a ratio of the enzyme's activity with FAD to the enzyme's activity without FAD. An AC of 1.2 to 1.4, riboflavin status is considered low when FAD is added to stimulate enzyme activity. An AC > 1.4 suggests riboflavin deficiency. On the other hand, if FAD is added and AC is < 1.2, then riboflavin status is considered acceptable. Tillotson and Bashor reported that a decrease in the intakes of riboflavin was associated with increase in EGR AC. In the UK study of Norwich elderly, initial EGR AC values for both males and females were significantly correlated with those measured 2 years later, suggesting that EGR AC may be a reliable measure of long-term biochemical riboflavin status of individuals. These findings are consistent with earlier studies.
- Experimental balance studies indicate that urinary riboflavin excretion rates increase slowly with increasing intakes, until intake level approach 1.0 mg/d, when tissue saturation occurs. At higher intakes, the rate of excretion increases dramatically. Once intakes of 2.5 mg/d are reached, excretion becomes approximately equal to the rate of absorption At such high intake a significant proportion of the riboflavin intake is not absorbed. If urinary riboflavin excretion is <19 µg/g creatinine or < 40 µg per day are indicative of deficiency.
Treatment
Medical uses
is a progressive thinning of the cornea; the most common form of this condition is keratoconus. Collagen cross-linking by applying riboflavin topically then shining UV light is a method to slow progression of corneal ectasia by strengthening corneal tissue.A 2017 review found that riboflavin taken daily in amounts roughly 200 to 400 times the Recommended Dietary Allowance may be useful to prevent migraines in adults, but found that clinical trials in adolescents and children had mixed outcomes. A hypothesis has been proposed that riboflavin improves mitochondrial energy production.
Pharmacokinetics
The body absorbs little riboflavin from single doses beyond 27 mg. When excess amounts are consumed, they are either not absorbed or the small amount that is absorbed is excreted in urine.After a single oral dose, biologic half-life is about 66 to 84 minutes in healthy people.
Side effects
In humans, there is no evidence for riboflavin toxicity produced by excessive intakes, in part because it has lower water solubility than other B vitamins, because absorption becomes less efficient as doses increase, and because what exceeds the absorption is excreted via the kidneys into urine. Even when 400 mg of riboflavin per day was given orally to subjects in one study for three months to investigate the efficacy of riboflavin in the prevention of migraine headache, no short-term side effects were reported. Any excess at nutritionally relevant doses is excreted in the urine, imparting a bright yellow color when in large quantities. The limited data available on riboflavin's adverse effects do not mean, however, that high intakes have no adverse effects, and the Food and Nutrition Board urges people to be cautious about consuming excessive amounts of riboflavin.Function
and flavin adenine dinucleotide function as cofactors for a variety of flavoprotein enzyme reactions:- Flavoproteins of electron transport chain, including FMN in Complex I and FAD in Complex II
- FAD is required for the production of pyridoxic acid from pyridoxal by pyridoxine 5'-phosphate oxidase
- The primary coenzyme form of vitamin B6 is FMN dependent
- Oxidation of pyruvate, α-ketoglutarate, and branched-chain amino acids requires FAD in the shared E3 portion of their respective dehydrogenase complexes
- Fatty acyl CoA dehydrogenase requires FAD in fatty acid oxidation
- FAD is required to convert retinol to retinoic acid via cytosolic retinal dehydrogenase
- Synthesis of an active form of folate from 5,10-methylenetetrahydrofolate by methylenetetrahydrofolate reductase is FADH2 dependent
- FAD is required to convert tryptophan to niacin
- Reduction of the oxidized form of glutathione to its reduced form by glutathione reductase is FAD dependent
Dietary recommendations
The National Academy of Medicine updated Estimated Average Requirements and Recommended Dietary Allowances for riboflavin in 1998. The current EARs for riboflavin for women and men ages 14 and up are 0.9 mg/day and 1.1 mg/day, respectively; the RDAs are 1.1 and 1.3 mg/day, respectively. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy is 1.4 mg/day. RDA for lactation is 1.6 mg/day. For infants up to 12 months the Adequate Intake is 0.3–0.4 mg/day. and for children ages 1–13 years the RDA increases with age from 0.5 to 0.9 mg/day. As for safety, the IOM sets Tolerable upper intake levels for vitamins and minerals when evidence is sufficient. In the case of riboflavin there is no UL, as there is no human data for adverse effects from high doses. Collectively the EARs, RDAs, AIs and ULs are referred to as Dietary Reference Intakes.The European Food Safety Authority refers to the collective set of information as Dietary Reference Values, with Population Reference Intake instead of RDA, and Average Requirement instead of EAR. AI and UL defined the same as in United States. For women and men ages 15 and older the PRI is set at 1.6 mg/day. PRI for pregnancy is 1.9 mg/day, for lactation 2.0 mg/day. For children ages 1–14 years the PRIs increase with age from 0.6 to 1.4 mg/day. These PRIs are higher than the U.S. RDAs. The EFSA also reviewed the safety question and like the U.S., decided that there was not sufficient information to set an UL.
For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value. For riboflavin labeling purposes 100% of the Daily Value was 1.7 mg, but as of May 27, 2016, it was revised to 1.3 mg to bring it into agreement with the RDA. Compliance with the updated labeling regulations was required by 1 January 2020, for manufacturers with $10 million or more in annual food sales, and by 1 January 2021 for manufacturers with less than $10 million in annual food sales. During the first six months following the 1 January 2020 compliance date, the FDA plans to work cooperatively with manufacturers to meet the new Nutrition Facts label requirements and will not focus on enforcement actions regarding these requirements during that time. A table of the old and new adult Daily Values is provided at Reference Daily Intake.
Other animals
In other animals, riboflavin deficiency results in lack of growth, failure to thrive, and eventual death. Experimental riboflavin deficiency in dogs results in growth failure, weakness, ataxia, and inability to stand. The animals collapse, become comatose, and die. During the deficiency state, dermatitis develops together with hair loss. Other signs include corneal opacity, lenticular cataracts, hemorrhagic adrenals, fatty degeneration of the kidney and liver, and inflammation of the mucous membrane of the gastrointestinal tract. Post-mortem studies in rhesus monkeys fed a riboflavin-deficient diet revealed about one-third the normal amount of riboflavin was present in the liver, which is the main storage organ for riboflavin in mammals. Riboflavin deficiency in birds results in low egg hatch rates.Chemistry
As a chemical compound, riboflavin is a yellow-orange solid substance with poor solubility in water compared to other B vitamins. Visually, it imparts color to vitamin supplements.Industrial uses
Because riboflavin is fluorescent under UV light, dilute solutions are often used to detect leaks or to demonstrate coverage in an industrial system such a chemical blend tank or bioreactor.Industrial synthesis
The industrial scale production of riboflavin using diverse microorganisms, including filamentous fungi such as Ashbya gossypii, Candida famata and Candida flaveri, as well as the bacteria Corynebacterium ammoniagenes and Bacillus subtilis. The latter organism, genetically modified to both increase the production of riboflavin and to introduce an antibiotic resistance marker, is employed at a commercial scale to produce riboflavin for feed and food fortification. The chemical company BASF has installed a plant in South Korea, which is specialized on riboflavin production using Ashbya gossypii. The concentrations of riboflavin in their modified strain are so high that the mycelium has a reddish/brownish color and accumulates riboflavin crystals in the vacuoles, which will eventually burst the mycelium. Riboflavin is sometimes overproduced, possibly as a protective mechanism, by some bacteria in the presence of high concentrations of hydrocarbons or aromatic compounds. One such organism is Micrococcus luteus, which develops a yellow color due to production of riboflavin while growing on pyridine, but not when grown on other substrates, such as succinic acid.History
The name "riboflavin" comes from "ribose" and "flavin", the ring-moiety which imparts the yellow color to the oxidized molecule. The reduced form, which occurs in metabolism along with the oxidized form, is colorless."Vitamin B" was originally considered to have two components, a heat-labile vitamin B1 and a heat-stable vitamin B2. In the 1920s, vitamin B2 was initially thought to be the factor necessary for preventing pellagra. In 1923, Paul Gyorgy in Heidelberg was investigating egg-white injury in rats; the curative factor for this condition was called vitamin H, which is now called biotin. Since both pellagra and vitamin H deficiency were associated with dermatitis, Gyorgy decided to test the effect of vitamin B2 on vitamin H deficiency in rats. He enlisted the service of Wagner-Jauregg in Kuhn's laboratory. In 1933, Kuhn, Gyorgy, and Wagner found that thiamin-free extracts of yeast, liver, or rice bran prevented the growth failure of rats fed a thiamin-supplemented diet.
Further, the researchers noted that a yellow-green fluorescence in each extract promoted rat growth, and that the intensity of fluorescence was proportional to the effect on growth. This observation enabled them to develop a rapid chemical and bioassay to isolate the factor from egg white in 1933. The same group then isolated the same preparation from whey using the same procedure. In 1934, Kuhn's group identified the structure of so-called flavin and synthesized vitamin B2, leading to evidence in 1939 that riboflavin was essential for human health.