OREGON STATE UNIVERSITY
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Riboflavin is a water-soluble B vitamin, also known as vitamin B2. Riboflavin is primarily found as an integral component of the coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) (1). Coenzymes derived from riboflavin are termed flavocoenzymes, and enzymes that use a flavocoenzyme are called flavoproteins (2).
Living organisms derive most of their energy from redox reactions, which are processes that involve the transfer of electrons. Flavocoenzymes participate in redox reactions in numerous metabolic pathways (3). They are critical for the metabolism of carbohydrates, lipids, and proteins. FAD is part of the electron transport (respiratory) chain, which is central to energy production. In conjunction with cytochrome P-450, flavocoenzymes also participate in the metabolism of drugs and toxins (4).
Glutathione reductase is a FAD-dependent enzyme that participates in the redox cycle of glutathione. The glutathione redox cycle plays a major role in protecting organisms from reactive oxygen species, such as hydroperoxides. Glutathione reductase requires FAD to regenerate two molecules of reduced glutathione from oxidized glutathione. Riboflavin deficiency has been associated with increased oxidative stress (4) Measurement of glutathione reductase activity in red blood cells is commonly used to assess riboflavin nutritional status (5).
Glutathione peroxidases (GPx), selenium-containing enzymes, require two molecules of reduced glutathione to break down hydroperoxides. GPx are involved in the glutathione oxidation-reduction (redox) cycle (Figure 1).
Xanthine oxidase, another FAD-dependent enzyme, catalyzes the oxidation of hypoxanthine and xanthine to uric acid. Uric acid is one of the most effective water-soluble antioxidants in the blood. Riboflavin deficiency can result in decreased xanthine oxidase activity, reducing blood uric acid levels (6).
Riboflavin (as FAD or FMN) is required for the synthesis of niacin from tryptophan, and in the metabolism of vitamin B6 and iron. It is also essential for folate and related one-carbon metabolism, where FAD is required as a cofactor for methylenetetrahydrofolate reductase (MTHFR), a key folate-metabolizing enzyme.
Flavoproteins are involved in the metabolism of several other vitamins: vitamin B6, niacin, vitamin B12, and folate. Therefore, low and deficient riboflavin status can affect several enzyme systems. The conversion of vitamin B6 to its active coenzyme form in tissues, pyridoxal 5'-phosphate (PLP), requires the FMN-dependent enzyme, pyridoxine 5'-phosphate oxidase (PPO) (7). Human studies have provided evidence of the metabolic dependency of vitamin B6 on riboflavin status in older (8-10) and younger (10) adults. The synthesis of the niacin-containing coenzymes, NAD and NADP, from the amino acid tryptophan, requires the FAD-dependent enzyme, kynurenine 3-monooxygenase. Severe riboflavin deficiency can thus decrease the conversion of tryptophan to NAD and NADP, increasing the risk of niacin deficiency (3).
Methylenetetrahydrofolate reductase (MTHFR) is an FAD-dependent enzyme that plays a key role in one-carbon metabolism by catalyzing the reduction of 5,10 methyleneTHF to 5 methylTHF. Once formed, 5 methylTHF is used by methionine synthase for the vitamin B12-dependent conversion of homocysteine to methionine and the formation of THF (Figure 2). Both FMN and FAD are coenzymes for the enzyme methionine synthase reductase, which is responsible for the regeneration of methylcobalamin, the biologically active form of vitamin B12 acting as a coenzyme for methionine synthase (11). Along with other B vitamins (folate, vitamin B12, and vitamin B6), higher dietary riboflavin intakes have been associated with lower plasma concentrations of homocysteine (12). In individuals homozygous for the C677T polymorphism in the MTHFR gene, low riboflavin status is associated with elevated plasma homocysteine, and in turn linked with a higher risk of cardiovascular disease and other chronic diseases (13, 14). Furthermore, supplementation with riboflavin results in marked lowering of homocysteine concentrations specifically in individuals with the variant MTHFR 677TT genotype (15). Such results illustrate that chronic disease risk may be influenced by complex interactions between genetic and dietary factors.
Riboflavin deficiency alters iron metabolism. Although the mechanism is not clear, research in animals suggests that riboflavin deficiency may impair iron absorption, increase intestinal loss of iron, and/or impair iron utilization for the synthesis of hemoglobin (16). In humans, low dietary intake of riboflavin has been associated with an increased risk for anemia (17), and improving riboflavin nutritional status has been found to increase circulating hemoglobin levels (18). Correction of riboflavin deficiency in individuals who are both riboflavin and iron deficient improves the response of iron-deficiency anemia to iron therapy (19). Anemia during pregnancy, a worldwide public health problem, is responsible for considerable perinatal morbidity and mortality (20, 21). The management of maternal anemia typically involves supplementation with iron alone or iron in combination with folic acid (22). It is possible that the inclusion of riboflavin could enhance the effects of iron-folic acid supplementation in treating maternal anemia, but the evidence is limited. There are, however, randomized, double-blind intervention trials conducted in pregnant women with anemia in Southeast Asia showing that a combination of folic acid, iron, vitamin A, and riboflavin improved hemoglobin levels and decreased anemia prevalence compared to iron-folic acid supplementation alone (23, 24).
Ariboflavinosis is the medical name for clinical riboflavin deficiency, which occurs commonly in low- and middle-income countries. Riboflavin deficiency is rarely found in isolation; it typically occurs in combination with deficiencies of other water-soluble vitamins. Clinical signs of riboflavin deficiency include sore throat, redness and swelling of the lining of the mouth and throat, cracks or sores on the outsides of the lips (cheliosis) and at the corners of the mouth (angular stomatitis), inflammation and redness of the tongue (magenta tongue), and a moist, scaly skin inflammation (seborrheic dermatitis). Other signs may involve the formation of blood vessels in the clear covering of the eye (vascularization of the cornea) and decreased red blood cell count in which the existing red blood cells contain normal levels of hemoglobin and are of normal size (normochromic normocytic anemia) (1, 3). Subclinical deficiency (low status) of riboflavin without clinical signs may be widespread, including in high-income countries, but usually goes undetected because riboflavin biomarkers are very rarely measured in human studies. Low or deficient riboflavin status may result in decreased conversion of vitamin B6 to its active coenzyme form (PLP) and decreased conversion of tryptophan to niacin (see Nutrient interactions).
Preeclampsia is defined as the presence of elevated blood pressure, protein in the urine, and edema (significant swelling) during pregnancy. About 5% of women with preeclampsia progress to eclampsia, a significant cause of maternal and fetal death. Eclampsia is characterized by seizures, in addition to high blood pressure and increased risk of hemorrhage (severe bleeding) (25). A study in 154 pregnant women at increased risk of preeclampsia found that those who were riboflavin deficient were 4.7 times more likely to develop preeclampsia than those who had adequate riboflavin nutritional status (26). The cause of preeclampsia-eclampsia is not known. Decreased intracellular levels of flavocoenzymes could cause mitochondrial dysfunction, increase oxidative stress, and interfere with nitric oxide release and thus blood vessel dilation – all of these changes have been associated with preeclampsia (26).
A 2015 meta-analysis of 54 case-control studies found that the MTHFR C677T polymorphism was associated with an increased risk of preeclampsia, especially in Caucasian and Asian populations (27). The reduction in the flavoprotein MTHFR activity observed in individuals with the variant MTHFR 677TT genotype leads to an increase in plasma homocysteine (14); higher homocysteine concentrations have been associated with preeclampsia (28). One small randomized controlled trial in 450 pregnant women in West Africa, without specified MTHFR genotype but at high risk for preeclampsia, found that supplementation with 15 mg of riboflavin daily was not effective in preventing the condition (29), but the study was likely underpowered to detect a significant effect. Further studies are needed to assess the potential benefit of riboflavin supplementation in reducing perinatal complications generally and specifically in preeclamptic women with the MTHFR 677TT genotype.
Alcoholics are at an increased risk of riboflavin deficiency, likely due to decreased dietary intake, decreased absorption, and/or impaired utilization of riboflavin. Interestingly, the elevated blood homocysteine concentrations associated with riboflavin deficiency rapidly decline during alcohol withdrawal (30). Additionally, people with anorexia rarely consume adequate dietary riboflavin, and those who are lactose intolerant are unlikely to meet requirements due to the avoidance of dairy products, the major dietary sources of riboflavin. The conversion of riboflavin into the active cofactor forms FAD and FMN is impaired in hypothyroidism and adrenal insufficiency (3, 4). Further, people who are very active physically (athletes, laborers) may have slightly increased riboflavin requirements. However, riboflavin supplementation has not generally been found to increase exercise tolerance or performance (31) unless the individuals are riboflavin deficient (32).
The RDA for riboflavin, revised in 1998, is based on the prevention of deficiency (Table 1). Clinical signs of deficiency in humans appear at intakes of less than 0.5 to 0.6 milligrams (mg)/day, and urinary excretion of riboflavin is seen at intake levels of approximately 1 mg/day (1).
| Life Stage | Age | Males (mg/day) | Females (mg/day) |
|---|---|---|---|
| Infants | 0-6 months | 0.3 (AI) | 0.3 (AI) |
| Infants | 7-12 months | 0.4 (AI) | 0.4 (AI) |
| Children | 1-3 years | 0.5 | 0.5 |
| Children | 4-8 years | 0.6 | 0.6 |
| Children | 9-13 years | 0.9 | 0.9 |
| Adolescents | 14-18 years | 1.3 | 1.0 |
| Adults | 19 years and older | 1.3 | 1.1 |
| Pregnancy | all ages | - | 1.4 |
| Breast-feeding | all ages | - | 1.6 |
Age-related cataracts are the leading cause of visual disability in the US and other developed countries. Research has focused on the role of nutritional antioxidants because of evidence that light-induced oxidative damage of lens proteins may lead to the development of age-related cataracts. A case-control study found significantly decreased risk of age-related cataracts (33% to 51%) in men and women in the highest quintile of dietary riboflavin intake (median of 1.6 to 2.2 mg/day) compared to those in the lowest quintile (median of 0.08 mg/day in both men and women) (33). Another case-control study reported that individuals in the highest quintile of riboflavin status, as measured by red blood cell glutathione reductase activity, had approximately one-half the occurrence of age-related cataract as those in the lowest quintile of riboflavin status, though the results were not statistically significant (34). A cross-sectional study of 2,900 Australian men and women, 49 years of age and older, found that those in the highest quintile of riboflavin intake were 50% less likely to have cataracts than those in the lowest quintile (35). A prospective cohort study of more than 50,000 women did not observe a difference between rates of cataract extraction between women in the highest quintile of riboflavin intake (median of 1.5 mg/day) and women in the lowest quintile (median of 1.2 mg/day) (36). However, the range between the highest and lowest quintiles was small, and median intake levels for both quintiles were above the RDA for riboflavin. A study in 408 women found that higher dietary intakes of riboflavin were inversely associated with a five-year change in lens opacification (37). A randomized controlled trial using a fractional factorial design showed that compared with placebo, the combined supplementation with riboflavin (3 mg/day) and niacin (40 mg/day) for five to six years reduced the prevalence of nuclear cataract but increased the progression of posterior subcapsular cataracts in population affected by multiple nutrient deficiency living in rural China (38). Of note is that the results of this trial are somewhat conflicting, and the study design does not allow the effects of riboflavin and niacin to be differentiated. In summary, there is some evidence predominantly from observational studies, that suggests higher riboflavin status might be beneficial; however, more evidence from well-designed, randomized controlled trials is needed to confirm a role for riboflavin in the prevention of cataracts.
The flavoprotein, methylenetetrahydrofolate reductase (MTHFR), plays a pivotal role in folate-mediated one-carbon metabolism. MTHFR converts 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, the cofactor form necessary for the re-methylation of homocysteine to methionine (see Figure 2 above). The conversion of homocysteine to methionine is of importance for homocysteine detoxification and for the production of S-adenosylmethionine (SAM), the methyl donor for the methylation of DNA and histones. Folate deficiency and elevated homocysteine concentrations may increase cancer risk (see the article on Folate). Aberrant methylation changes are also known to alter the structure and function of DNA and histones during cancer development (39). Since MTHFR controls the detoxification of homocysteine and the supply of methyl groups for SAM synthesis, a reduction in its activity can affect homocysteine metabolism and disturb cellular methylation processes. The substitution of a cytosine by a thymine in position 677 (c.677C>T) in the MTHFR gene is a polymorphism that affects the binding of FAD and leads to an increased propensity for MTHFR to lose its flavin coenzyme (40). Subjects homozygous for this mutation (MTHFR 677TT genotype) exhibit reduced MTHFR activity and increased risk for a wide variety of cancers (41-43), but the evidence of an association between this polymorphism and cancer is inconsistent, with some reports suggesting a reduction in colorectal cancer risk with the T allele (44).
As mentioned above (see B-complex vitamins), riboflavin intake is a determinant of homocysteine concentration. This suggests that riboflavin status can influence MTHFR activity and the metabolism of folate, thereby affecting cancer risk (43). In a randomized, double-blind, placebo-controlled study, 93 subjects with colorectal polyps and 86 healthy subjects were given a placebo, folic acid (400 or 1,200 μg/day), or folic acid (400 μg/day) plus riboflavin (5 mg/day) for 45 days. These interventions significantly improved folate and riboflavin status in vitamin-supplemented individuals compared to those taking the placebo. Interestingly, riboflavin enhanced the effect of 400 μg folic acid on circulating 5-methyltetrahydrofolate (5-MTHF) specifically in the polyp patients with the C677T genetic variant (45). This suggests that riboflavin may improve the response to folic acid supplementation in individuals with a reduced MTHFR activity. Additionally, a prospective cohort study of 88,045 postmenopausal women found total (dietary plus supplemental) intake of riboflavin to be inversely correlated with colorectal cancer risk when comparing the highest (>3.97 mg) and lowest (<1.80 mg) quartiles of daily intake (46); intake in the reference group was well above the RDA for riboflavin of 1.1 mg/day. The subjects in this study were not prescreened to identify those with the variant MTHFR 677TT genotype, and the association between this polymorphism and colorectal cancer remains unclear, with some reports suggesting a reduction in cancer risk with the T allele (44). Two meta-analyses have found inverse associations between riboflavin intake and risk of colorectal cancer (47, 48). The most recent of these was a dose-response meta-analysis that pooled results from five prospective cohort studies, nine case-control studies, and two studies reporting blood concentrations of riboflavin. This analysis found that higher intakes of riboflavin were associated with a significantly lower risk of colorectal cancer (RR=0.87; 95% CI, 0.81-0.93); inverse associations were observed for both dietary riboflavin intake and total daily intake from the diet and supplements (48).
Associations between riboflavin intake and cancer risk have also been evaluated in other types of cancer. A seven-year intervention study evaluated the use of riboflavin-fortified salt in 22,093 individuals at high risk for esophageal cancer in China. Riboflavin status and esophageal pathology (percent normal, dysplastic, and cancerous tissues) improved in the intervention group compared to the control group, but the lower incidence of esophageal cancer found in the intervention group was not statistically significant (49). Additionally, a 25-year follow up of an intervention trial in patients at high risk for gastric cancer found that dietary supplementation with riboflavin (3.2 mg/day) and niacin (40 mg/day) for five years decreased the risk of mortality from esophageal cancer by 8% but had no effect on mortality from gastric cancer (50). In the Melbourne Collaborative Cohort Study, which followed 41,514 men and women over a 15-year period, weak inverse associations were found between riboflavin intake and lung cancer (51) and breast cancer (52); no association of riboflavin intake with prostate cancer was observed in this cohort (53). A 2017 meta-analysis of 10 observational studies found an overall inverse association of riboflavin intake and breast cancer incidence and reported a 6% lower risk with each 1 mg/day increment of riboflavin intake (54). Further, studies to date have not found riboflavin intake or measures of riboflavin status to be associated with renal cell carcinoma, as reviewed in a recent meta-analysis (55).
Some evidence indicates that impaired mitochondrial oxygen metabolism in the brain may play a role in the pathology of migraine headaches. Since riboflavin is the precursor of the two flavocoenzymes (FAD and FMN) required by the flavoproteins of the mitochondrial electron transport chain, supplemental riboflavin has been investigated as a treatment for migraine. A randomized controlled trial examined the effect of very high dose riboflavin (400 mg/day) for three months on migraine prevention in 54 men and women with a history of recurrent migraine headaches (56). Riboflavin compared to placebo reduced attack frequency and the number of headache days, though the beneficial effect was most pronounced during the third month of treatment (56). Another study by the same investigators found that treatment with either a β-blocker drug or high-dose riboflavin (400 mg/day) for four months resulted in clinical improvement, but each therapy appeared to act on a distinct pathological mechanism: β-blockers on abnormal cortical information processing and riboflavin on decreased brain mitochondrial energy reserve (57). A small study in 23 patients reported a reduction in median migraine attack frequency after supplementation with 400 mg of riboflavin daily for three months (58). A single-blinded, randomized, parallel group trial in 85 patients with migraine headaches (ages 15-55 years), high-dose riboflavin supplementation (400 mg/day) for 12 weeks decreased migraine frequency, duration, and severity compared to baseline and was as effective as sodium valproate (500 mg/day) (59), a medication with established efficacy in migraine preventative therapy (60). Riboflavin elicited significantly fewer adverse effects compared to the drug (59). Thus, although the available trials have been small and short term, most studies to date suggest that high-dose riboflavin supplementation might be a useful adjunct therapy in adults with migraine headaches.
A few randomized controlled trials have investigated the effect of riboflavin supplementation on the frequency and severity of headache attacks in children with migraines. An initial study evaluated riboflavin at 200 mg/day for 12 weeks in 48 children of ages 5 to 15 years old (61). A second study was a cross-over trial with half of the 42 children, ages 6 to 13, receiving 50 mg/day riboflavin for 16 weeks then placebo (100 mg/day carotene) for 16 weeks (with a four-week washout period in between each), while the other half were first given the placebo then riboflavin (62). Neither study showed differences in the frequency, duration, or intensity of migraines between treatments. However, a more recent trial found a benefit of intervention with higher dose riboflavin: children with migraine treated with 400 mg/day of riboflavin for 12 weeks (n=30) had reductions in migraine frequency and duration, but not intensity, compared to placebo (n=30), yet no benefit was seen in children taking 200 mg/day for 12 weeks in this study (63). Additionally, a randomized controlled trial in 98 adolescents, ages 12 to 19 years, found that 400 mg/day of riboflavin for three months decreased both headache frequency and duration and improved migraine-related disability compared to placebo (64). Retrospective studies of children and adolescents suffering from migraine have also suggested some benefit associated with supplemental riboflavin (65-67). Thus, studies to date are somewhat conflicting, and more research is needed to understand whether riboflavin supplementation might have utility in the treatment of childhood migraine and the most effective dose required for any beneficial effects.
Increasing evidence from case reports indicates that patients with autosomal recessive disorders caused by defective FAD-dependent enzymes could benefit from riboflavin supplementation.
MADD, also known as type II glutaric aciduria (or acidemia), is a fatty acid metabolism disorder characterized by the accumulation of short-, medium-, and long-chain acyl-carnitines in various tissues. MADD is classified into three separate types based on age of onset and clinical symptoms: type I MADD is evident in the neonatal period and is characterized by the presence of congenital anomalies; type II MADD is present in the neonatal period but lacks congenital defects; and type III is characterized by late onset, from infancy through adulthood (68), and even as late as the seventh decade of life (69). Clinical symptoms of type I and II MADD present shortly after birth and include hypoglycemia, hyperammonemia, metabolic acidosis, hepatomegaly, and respiratory distress (68, 70); these forms of MADD are often fatal in infancy, even if treated. Type III MADD usually presents later in life and includes milder symptoms, varying from periodic vomiting, rhabdomyolysis, muscle pain and weakness, and exercise intolerance (68, 70). Peripheral neuropathy has also recently been reported as a symptom of adult-onset MADD (71).
MADD is caused by autosomal recessive mutations in genes that impair the activity of enzymes involved in the transfer of electrons from acyl-coenzyme A (acyl-CoA) to coenzyme Q10/ubiquinone inside the mitochondria (Figure 3). ETFA, ETFB, and ETFDH code for the two subunits of the electron transfer flavoprotein (ETF-A and -B) and for ETF dehydrogenase/ubiquinone oxidoreductase (ETFDH/ETFQO), respectively. Deficiencies in these enzymes (ETF or ETFDH) lead to a decrease in oxidized FAD, which becomes unavailable for FAD-dependent dehydrogenation reactions, including the first step in β-oxidation – a major fatty acid catabolic process that takes place in the mitochondria. A defect in fatty acid β-oxidation causes lipid accumulation in skeletal muscles, leading to lipid storage myopathy characterized by muscle pain and weakness and exercise intolerance.
Together with a low-fat, high-carbohydrate diet, riboflavin supplementation has led to significant clinical improvements in patients with ETFDH mutations. The specific type of the mutation in ETF/ETFDH contributes to age of onset, severity, and responsiveness to riboflavin treatment (70, 72). Additionally, the report of a 20-year-old man with riboflavin-responsive MADD failed to find mutations in ETF and ETFDH genes, suggesting that other sites of mutation should not be excluded (73). Finally, secondary deficiencies in the respiratory chain are observed in MADD and appear to respond favorably to riboflavin supplementation (72, 74).
Acyl-CoA dehydrogenase family member 9 (ACAD9) is an FAD-dependent enzyme with important roles in both the electron transport chain and β-oxidation of fatty acids in the mitochondria. Recessive mutations in the ACAD9 gene coding for ACAD9 have been found in patients with mitochondrial complex I deficiency, a respiratory chain disorder (75). Complex I carries electrons from NADH to coenzyme Q10 in the electron transport chain. Defective oxidative phosphorylation (ATP synthesis by the respiratory chain) due to complex I deficiency has been linked to a broad variety of clinical manifestations, from neonatal death to late-onset neurodegenerative diseases. The clinical symptoms of complex I deficiency due to ACAD9 mutations typically include muscle weakness, exercise intolerance, lactic acidosis, and hypertrophic cardiomyopathy (76). However, symptoms can be of varying severity, likely due to the remaining functional activity of ACAD9. For example, affected patients have been reported to exhibit a spectrum of cardiac deficits, including isolated, mild ventricular hypertrophy to severe hypertrophic cardiomyopathy (77).
Riboflavin supplementation (100-300 mg/day) has been shown to increase complex I activity in patients with childhood-onset clinical forms of ACAD9 deficiency. Improvements in muscle strength and exercise tolerance have also been associated with riboflavin supplementation (78-80). A review of cases of ACAD9 deficiency presenting in infancy (i.e., cases with severe symptoms) found riboflavin treatment to be associated with improved survival: 7 of 22 patients treated with riboflavin succumbed to the illness compared to 16 out of 17 untreated patients (76).
SLC52A1, SLC52A2, and SLC52A3 genes code for the human riboflavin transporters RFVT1, RFVT2, and RFVT3, respectively. Mutations in these genes lead to riboflavin transporter deficiency, a rare neurodegenerative condition with variable age of onset, from infancy to early stages of adulthood. Autosomal recessive mutations in SLC52A2 or SLC52A3 respectively cause disorders known as riboflavin transporter deficiency type 2 (RFVT2 deficiency) and riboflavin transporter deficiency type 3 (RFVT3 deficiency). These genetic disorders were formerly called Brown-Vialetto-Van Laere syndrome and Fazio-Londe syndrome (81). Riboflavin transporter deficiency caused by mutation of SLC52A1 is exceedingly rare and has been reported in only three cases (reviewed in 82).
Clinical features of riboflavin transporter deficiency can include muscle weakness in the arms and legs, sensory ataxia, bulbar palsy with hypotonia and facial weakness, sensorineural deafness, and respiratory insufficiency (83, 84). High-dose, oral supplementation with riboflavin improves many of these symptoms in the majority of affected patients; such treatment should be given at the time of suspected riboflavin transporter deficiency for a better prognosis (84). A 2016 review of the published literature found that oral supplementation with riboflavin – at doses ranging from 7 to 60 mg/kg/day – led to improved symptoms in 71% of the patients (n=39) and to no deaths (83). In contrast, all of the untreated patients (n=31) had a progression of the disease and a mortality rate of at least 48% (83).
Primary trimethylaminuria is caused by defective oxidation of trimethylamine by a liver flavoprotein called flavin containing mono-oxygenase 3 (FMO3). Individuals with FMO3 deficiency have increased levels of trimethylamine in urine, sweat, and breath (85). This socially distressing condition is known as "fish odor syndrome" due to the fishy odor and volatile nature of trimethylamine. FMO3 gene mutations are usually associated with mild or intermittent trimethylaminuria; the condition is sometimes limited to peri-menstrual periods in female subjects or to the consumption of trimethylamine-rich food. The clinical management of the condition includes dietary restriction of trimethylamine and its precursors, such as foods rich in choline and seafood, as well as cruciferous vegetables that contain both trimethylamine precursors and FMO3 antagonists (86). The use of riboflavin supplements was reported in a 17-year-old female patient affected by pyridoxine non-responsive homocystinuria (87). The disease was initially treated with betaine (a choline derivative), which caused body odor secondary to FMO3 deficiency. Riboflavin supplementation (200 mg/day) reduced trimethylamine excretion and the betaine treatment-related body odor. Similar effects were seen with riboflavin supplementation in two pediatric patients (88). The data suggest that riboflavin might help maximize residual FMO3 enzyme activity in patients with primary trimethylaminuria. Moreover, a recent case report in a 35-year-old male with HIV described supplemental riboflavin as an effective treatment for secondary trimethylaminuria caused by antiretroviral therapy (89).
Hypertension in adulthood is recognized as the leading risk factor contributing to mortality worldwide primarily from cardiovascular disease, while hypertension in pregnancy leads to serious adverse fetal and maternal outcomes. A number of risk factors are recognized to contribute to the development of hypertension. In recent years, evidence has emerged from genetic and clinical studies pointing to the role of one-carbon metabolism in blood pressure (90). The common MTHFR C677T polymorphism, affecting 1 in 10 adults globally, is associated with higher blood pressure, although this is much less well recognized compared with the phenotype of elevated homocysteine concentrations that was established at the time of discovery of this polymorphism and its link with cardiovascular disease (91). Meta-analyses show that this polymorphism is associated with an increased risk of hypertension by up to 87% and of heart disease and stroke by up to 40% (92). The MTHFR C677T polymorphism is also associated with a significantly higher risk of hypertension in pregnancy (93) and with preeclampsia (27).
Since FAD is required as a cofactor for the MTHFR enzyme and the MTHFR C677T polymorphism results in decreased MTHFR activity, studies have investigated whether affected individuals may benefit from riboflavin supplementation. In an initial randomized controlled trial in 77 healthy young adults stratified by MTHFR genotype, riboflavin supplementation at dietary levels (1.6 mg/day for 12 weeks) resulted in marked lowering of homocysteine concentrations in the MTHFR 677TT genotype group, but not in the 677CC or 677CT genotype groups who exhibited normal plasma homocysteine at baseline (15). Three randomized controlled trials subsequently investigated the effect of riboflavin on blood pressure in patients with hypertension with or without overt cardiovascular disease (91, 94, 95). The results of these trials showed that supplementation with low-dose riboflavin (1.6 mg/day for 16 weeks) resulted in significant lowering of blood pressure and reduction in incidence of hypertension specifically in those patients with the variant MTHFR 677TT genotype. Riboflavin intervention reduced mean systolic/diastolic blood pressure in those with the TT genotype from 144/87 to 131/80 mm Hg, with no response observed in those without the genetic variant (i.e., the CT or CC genotypes) (89). Notably, the 13 mm Hg decrease in systolic blood pressure occurred even though over 80% of the patients were taking one or more antihypertensive drugs at recruitment, and the addition of supplemental riboflavin was shown to greatly enhance the achievement of goal blood pressure with routine antihypertensive drugs (89, 91). Furthermore, the magnitude of blood pressure response achieved with riboflavin in these trials compares very favorably with typical decreases from other interventions, such as dietary salt reductions of 3 g/day (3.6/1.9 mm Hg) and 6 g/day (7.1/3.9 mm Hg). The trial findings therefore suggest that the excess risk of hypertension linked to this genetic polymorphism can be overcome by low-dose riboflavin supplementation. Also, analysis of plasma samples from individuals participating in these trials showed lower concentrations of S-adenosylmethionine (SAM), an important methyl group donor for methylation reactions, in those with the MTHFR 677TT genotype versus the CC genotype (96). However, riboflavin supplementation (1.6 mg/day) for 12 weeks was shown to increase plasma concentrations of SAM and another one-carbon metabolite, cystathionine (96), and thus may have potential in correcting the altered one-carbon metabolism arising with the variant TT genotype.
Thus, studies to date indicate that riboflavin supplementation may have benefits in lowering blood pressure and reducing hypertension in individuals (and sub-populations) affected by the common MTHFR C677T polymorphism. However, the mechanisms explaining the blood pressure phenotype and its responsiveness to riboflavin remain unclear. Future studies examining the effects of riboflavin supplementation on one-carbon metabolism may help to elucidate the biological mechanisms involved. Interestingly, a recent randomized controlled trial found that riboflavin supplementation in those with the variant MTHFR 677TT genotype resulted in altered DNA methylation of certain genes known to be involved in blood pressure regulation (97).
Anticancer agents often display various side effects that may force patients to limit the dose or to discontinue the treatment. The antioxidant effect of co-administering riboflavin (10 mg/day), niacin (50 mg/day), and coenzyme Q10 (100 mg/day) was evaluated in 78 postmenopausal patients with breast cancer treated with tamoxifen for 90 days. This supplementation effectively prevented the oxidative stress associated with tamoxifen treatment (98).
Riboflavin can also act as a photosensitizer, and this property may have value in photodynamic therapy of cancer. A mouse model was used to assess the effect of riboflavin in combination with cisplatin, one of the most effective anticancer agents. Under light exposure, riboflavin administration reduced cisplatin-induced DNA damage in the liver and kidneys (99). These results are promising, but human studies are needed to examine whether riboflavin is an effective adjunct to chemotherapy.
Corneal ectasia is an eye condition characterized by irregularities of the cornea that affect vision. Corneal cross-linking – a fairly new procedure used by professionals to limit the progression of corneal damage –involves the use of topical riboflavin in conjunction with ultraviolet-A irradiation. Riboflavin functions as a photosensitizer in the reaction. Cross-linking modifies the properties of the cornea and strengthens its architecture (100, 101).
Multiple sclerosis (MS) is an autoimmune disease of unknown etiology that is characterized by the progressive destruction of myelin and nerve fibers in the central nervous system, causing neurological symptoms in affected individuals (102). Riboflavin appears to have a role in the formation of myelin (103), and oxidative stress has been implicated in the pathogenesis of MS; thus, riboflavin may be helpful in treatment of the disease. A strong inverse association between dietary riboflavin intake and risk for MS was initially observed in a case-control study (104). In a mouse model of MS (i.e., experimental autoimmune encephalomyelitis), riboflavin supplementation improved clinical measures of the disease (105). However, a randomized, double-blind, placebo-controlled pilot study in 29 patients with MS found that supplementation with 10 mg/day of riboflavin for six months had no effect on MS-related disability, assessed by the Expanded Disability Status Scale (106). Large-scale randomized, placebo-controlled trials are needed to determine whether riboflavin supplementation has a beneficial effect in the treatment of MS.
Most plant- and animal-derived foods contain at least small quantities of riboflavin. In the US, wheat flour and bread have been enriched with riboflavin (as well as thiamin, niacin, and iron) since 1943. Data from a US national survey indicate that the average dietary intake of riboflavin is 2.5 mg/day for men and 1.8 mg/day for women (107); these intakes are well above the RDA values of 1.3 mg/day for men and 1.1 mg/day for women. Surveys of adults of ages 70 years or older showed similar intakes: 2.2 mg/day for older men and 1.8 mg day for older women (107).
Riboflavin is heat-stable, but it is easily destroyed upon exposure to light. For instance, up to 50% of the riboflavin in milk contained in a clear glass bottle can be destroyed after two hours of exposure to bright sunlight 6. Nationally representative surveys from the US, Ireland, and the UK showed that milk and other dairy products were the main dietary contributors to riboflavin intake, followed by meat and ready-to-eat breakfast cereals (108-110). Some foods with substantial amounts of riboflavin are listed in Table 2, along with their riboflavin content in milligrams (mg). For more information on the nutrient content of food, search USDA's FoodData Central.
The bioavailability of riboflavin from food is reported to be very high, nearly 95% (108). Limited data exist for the relative bioavailability of riboflavin from different food sources, however a cross-over study in healthy women using stable isotopes and kinetic modeling did not find significant differences in riboflavin absorption from milk and spinach (111).
The most common forms of riboflavin available in supplements are riboflavin and riboflavin 5'-monophosphate. Riboflavin is commonly found in multivitamin and vitamin B-complex preparations (112).
No toxic or adverse effects of high riboflavin intake in humans are known. Studies in cell culture indicate that excess riboflavin may increase the risk of DNA strand breaks in the presence of chromium (VI), a known carcinogen (113). This may be of concern to workers exposed to chrome, yet no data in humans are available. High-dose riboflavin therapy has been found to intensify urine color to a bright yellow (flavinuria), but this is a harmless side effect. The Food and Nutrition Board did not establish a tolerable upper intake level (UL) when the RDA was revised in 1998 (1).
Several early reports indicated that women taking high-dose oral contraceptives had diminished riboflavin biomarker status. However, when investigators controlled for dietary riboflavin intake, no differences between users of oral contraceptives and non-users were found (1). Phenothiazine derivatives like the anti-psychotic medication, chlorpromazine (Thorazine), and tricyclic antidepressants inhibit the conversion of riboflavin to FAD and FMN, as do the anti-malarial medication, quinacrine, and the cancer chemotherapy agent, adriamycin (4). Long-term use of the anticonvulsant, phenobarbitol, may increase destruction of riboflavin by liver enzymes, increasing the risk of deficiency (3). Additionally, chronic alcohol consumption has been associated with riboflavin deficiency. In rats chronically fed alcohol, the inhibition of riboflavin transporters caused impairment in intestinal absorption and renal re-uptake of the vitamin (114).
The RDA for riboflavin (1.3 mg/day for men and 1.1 mg/day for women), which should prevent deficiency in most individuals, is easily met by eating a varied diet. Consuming a varied diet should supply 1.5 mg to 2 mg of riboflavin a day. Following the Linus Pauling Institute recommendation to take a multivitamin/mineral supplement containing 100% of the Daily Values (DV) will ensure an intake of at least 1.3 mg/day of riboflavin.
Some experts in nutrition and aging feel that the RDA (1.3 mg/day for men and 1.1 mg/day for women) leaves little margin for error in people over 50 years of age (115, 116). A study of independently living people between 65 and 90 years of age found that almost 25% consumed less than the recommended riboflavin intake, and 10% had biochemical evidence of deficiency (117). Epidemiological studies of cataract prevalence indicate that riboflavin intakes of 1.6 to 2.2 mg/day may reduce the risk of developing age-related cataracts. Additionally, older people suffering from acute ischemic stroke were found to be deficient for riboflavin (118), and riboflavin deficiency has been linked to a higher risk of fracture in postmenopausal women with the MTHFR 677T variant (119). Individuals whose diets may not supply adequate riboflavin, especially those over 50 years of age, should consider taking a multivitamin/mineral supplement, which generally provides at least 1.3 mg/day of riboflavin.
Originally written in 2000 by:
Jane Higdon, Ph.D.
Linus Pauling Institute
Oregon State University
Updated in September 2002 by:
Jane Higdon, Ph.D.
Linus Pauling Institute
Oregon State University
Updated in June 2007 by:
Victoria J. Drake, Ph.D.
Linus Pauling Institute
Oregon State University
Updated in July 2013 by:
Barbara Delage, Ph.D.
Linus Pauling Institute
Oregon State University
Updated in August 2021 by:
Victoria J. Drake, Ph.D.
Linus Pauling Institute
Oregon State University
Reviewed in July 2022 by:
Kristina Pentieva, MD, Ph.D. and Helene McNulty, RD, Ph.D.
Nutrition Innovation Centre for Food and Health (NICHE)
Ulster University, Coleraine, Northern Ireland
Copyright 2000-2023 Linus Pauling Institute
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