Short answer. Adults need 1.1 to 1.3 mg of riboflavin (vitamin B2) a day, and children aged 1 to 13 need 0.5 to 0.9 mg, according to the NIH Office of Dietary Supplements. No upper limit has been set. The body absorbs little beyond about 27 mg at once, and the extra leaves in bright yellow urine.
Riboflavin and riboflavin 5'-phosphate at a glance
| Riboflavin (free form) | Riboflavin 5'-phosphate (R5P, FMN) | |
|---|---|---|
| What it is | The form in most supplements, and the main form in milk and eggs | One of the two coenzyme forms cells use; found in some supplements |
| In food | More than 90% of riboflavin in food is bound as FMN or FAD (NIH ODS) | |
| Absorption | Free riboflavin is about as bioavailable as FMN and FAD (NIH ODS); about 95% of food riboflavin is absorbed, up to about 27 mg per meal or dose | |
| Upper limit | None set for either form; the Food and Nutrition Board still urges caution with very large amounts | |
Source: NIH Office of Dietary Supplements; PubMed records under Sources.
What does vitamin B2 do in the body?
Riboflavin is one of the water-soluble B vitamins. Cells turn it into two coenzymes: flavin mononucleotide (FMN, also called riboflavin 5'-phosphate) and flavin adenine dinucleotide (FAD). These helper molecules take part in energy production, in normal cell function, growth and development, and in the metabolism of fats, drugs and steroids (NIH Office of Dietary Supplements).
Riboflavin also keeps other B vitamins working. FMN is needed to turn vitamin B6 into its active form, pyridoxal 5'-phosphate, and FAD is needed to make niacin from the amino acid tryptophan. Riboflavin helps maintain normal blood levels of homocysteine, together with folate and vitamin B12. When riboflavin runs seriously low, the metabolism of these other B vitamins can suffer too (NIH ODS).
The body keeps only small stores, mostly in the liver, heart and kidneys (NIH ODS).
How much vitamin B2 do children and adults need?
The Food and Nutrition Board sets a Recommended Dietary Allowance (RDA) for riboflavin from age 1. For babies it sets an Adequate Intake (AI) equal to what healthy breastfed infants take in. The Daily Value on US labels is 1.3 mg for adults and children aged 4 and older.
| Age | Male | Female | Pregnancy | Lactation | Upper limit (UL) |
|---|---|---|---|---|---|
| Birth to 6 months (AI) | 0.3 mg | 0.3 mg | Not set | ||
| 7 to 12 months (AI) | 0.4 mg | 0.4 mg | Not set | ||
| 1 to 3 years | 0.5 mg | 0.5 mg | Not set | ||
| 4 to 8 years | 0.6 mg | 0.6 mg | Not set | ||
| 9 to 13 years | 0.9 mg | 0.9 mg | Not set | ||
| 14 to 18 years | 1.3 mg | 1.0 mg | 1.4 mg | 1.6 mg | Not set |
| 19 to 50 years | 1.3 mg | 1.1 mg | 1.4 mg | 1.6 mg | Not set |
| 51 years and older | 1.3 mg | 1.1 mg | Not set |
Source: NIH Office of Dietary Supplements, Riboflavin fact sheet for health professionals (Table 1).
Most people in the United States already get enough. In national survey data from 2003 to 2006, fewer than 6% of people had a riboflavin intake from food and supplements below the average requirement. Children aged 2 to 5 average 1.8 mg a day from food alone, children aged 6 to 11 average 1.9 mg, and teens 2.1 mg. Adult men average 2.5 mg and women 1.8 mg from food (NIH ODS). If your child takes a supplement, the dose belongs to their pediatrician, who can weigh it against what your child already eats.
Which foods have the most riboflavin?
Eggs, organ meats, lean meats and milk are the richest sources, and grains and cereals are fortified with riboflavin in the United States. Milk and milk drinks, bread and ready-to-eat cereals are the largest contributors to what Americans eat (NIH ODS). Some examples from the NIH food table:
- Beef liver, pan fried, 3 ounces: 2.9 mg
- Breakfast cereal fortified with 100% of the Daily Value, 1 serving: 1.3 mg
- Instant oats, fortified, 1 cup cooked: 1.1 mg
- Plain fat-free yogurt, 1 cup: 0.6 mg
- Milk, 2%, 1 cup: 0.5 mg
- Almonds, dry roasted, 1 ounce: 0.3 mg
- Egg, 1 large: 0.2 mg
- Raw spinach, 1 cup: 0.1 mg
Plant sources count. In a crossover study of 20 healthy women aged 18 to 65 using labeled riboflavin, absorption from spinach (60%) and from milk (67%) was not significantly different by urinary monitoring (Dainty 2007).
Boiling loses about twice as much riboflavin as steaming or microwaving, and light breaks it down, which is why milk is rarely sold in clear glass (NIH ODS).
Is riboflavin 5'-phosphate better than regular riboflavin?
For meeting your daily needs, the evidence does not favor one over the other. Most riboflavin in food arrives as FMN or FAD, and the NIH notes that free riboflavin is about as bioavailable as FMN and FAD. Most supplements use the free form, and some use riboflavin 5'-phosphate (NIH ODS).
A label that says "R5P" is a choice of form, not a stronger dose. The amount per serving matters more, because of the absorption ceiling described below.
Can you take too much vitamin B2, and why does it turn urine yellow?
No Tolerable Upper Intake Level has been set for riboflavin. Intakes from food many times the RDA have shown no toxicity, possibly because riboflavin dissolves poorly and the gut can only absorb so much. The Food and Nutrition Board found no reports of harm from high intakes, including 400 mg a day for at least 3 months, but it also stressed that limited data do not prove large intakes are free of risk, and it urges caution (NIH ODS).
At 400 mg a day, side effects in studies were minor. In a 3-month randomized trial in which 55 adults took 400 mg of riboflavin or a placebo, two people in the riboflavin group reported diarrhea or more frequent urination, and one person in the placebo group reported stomach cramps; none of these events was serious (Schoenen 1998). Doses that high are far above the RDA and are a decision for a doctor, not a default.
The bright yellow, almost neon, urine many people notice after a B-complex is riboflavin the body did not need. Riboflavin is naturally yellow, the body stores little, and the extra goes out in urine (NIH ODS). It is expected and harmless. The absorption ceiling is measurable: when 9 healthy adults took single oral doses of 20, 40 and 60 mg, the most that could be absorbed from one dose was about 27 mg, and urine accounted for about half of the riboflavin cleared from the blood (Zempleni 1996).
Does vitamin B2 interact with medicines?
According to the NIH Office of Dietary Supplements, riboflavin is not known to have any clinically relevant interactions with medications. It is still worth telling your doctor and pharmacist about every supplement you take.
Light is the one practical exception to note. Long sessions of light therapy, such as phototherapy for newborn jaundice, can deplete riboflavin, because light breaks it down (NIH ODS).
Who is more likely to run low on riboflavin?
Riboflavin deficiency is extremely rare in the United States. The NIH lists these groups as more likely to have low status (NIH ODS):
- Vegans and people who drink little milk, because dairy and eggs supply much of the riboflavin in Western diets.
- Vegetarian athletes, since exercise increases demand on riboflavin-dependent pathways.
- Pregnant or breastfeeding women who rarely eat meat or dairy.
- People with riboflavin transporter deficiency, a rare inherited condition managed by specialists.
Signs that can point to low riboflavin include cracks or sores at the corners of the mouth, swollen and cracked lips, a sore, red throat, itchy and red eyes, skin changes and hair loss. People who are low in riboflavin are usually low in other nutrients too (NIH ODS). These signs are reasons to see a doctor and get tested, not to start a high dose on your own.
The usual lab test is the erythrocyte glutathione reductase activity coefficient (EGRAC). A value of 1.2 or less usually means adequate status, 1.2 to 1.4 marginal, and above 1.4 deficient, although the exact cutoffs are debated and the test does not work in people with G6PD deficiency (NIH ODS). A systematic review of 18 supplementation studies found EGRAC was an effective marker of changes in riboflavin intake (Hoey 2009).
What do the studies show about riboflavin, iron and MTHFR?
Iron status. In the RIBOFEM trial, 123 women aged 19 to 25 in the United Kingdom with low riboflavin status (EGRAC above 1.40) took 2 mg or 4 mg of riboflavin or a placebo for 8 weeks; 119 finished. Riboflavin status improved with dose, and rises in hemoglobin tracked the improvement in riboflavin status. Women who started lowest (EGRAC above 1.65) saw the largest hemoglobin change. Iron intake and iron absorption did not change (Powers 2011). The authors concluded that moderately poor riboflavin status can affect iron status.
The MTHFR 677TT variant. The MTHFR enzyme, which makes the active form of folate, uses FAD as its cofactor. In people with two copies of the common 677C→T variant (the TT genotype), the enzyme tends to lose that cofactor. In a 12-week trial in healthy adults aged 18 to 65 (35 TT, 26 CT and 28 CC), 1.6 mg of riboflavin a day improved riboflavin status in every group, but homocysteine fell only in the TT group: by as much as 22% overall, and by 40% in those whose riboflavin status was lower at the start (McNulty 2006). The dose here was close to the RDA, not a megadose. If you know your MTHFR result, ask your doctor whether your riboflavin intake is worth checking alongside folate.
Which ASDHelp products contain riboflavin?
Doses are copied from each label. There is no upper limit for riboflavin, but every product below gives several times the RDA, and the body absorbs only about 27 mg from a single dose, so a larger single serving mostly ends up in urine. If you use more than one product, add up the total.
- Spectrum B Complex + Benfotiamine: 20 mg of riboflavin (as riboflavin 5'-phosphate sodium) per capsule, with the other B vitamins. Label directions: 1 capsule once or twice daily; no children's dose.
- Formula C: 15 mg of riboflavin per 6 capsules, in a broad multivitamin and mineral formula. Label directions: adults and children 4 years and older, 6 capsules daily with food; under 4, as directed by a healthcare professional.
- Spectrum Formula Chewable + Iron: 5 mg of riboflavin (as riboflavin and riboflavin 5'-phosphate sodium) per 4 chewable tablets, in a multivitamin with 3 mg of iron. Label directions: ages 1 to 3, 1 to 2 tablets twice daily; 4 and older, 2 to 4 tablets twice daily. Keep it out of children's reach because it contains iron.
- MITOboost Protein Powder Strawberry: 15 mg of riboflavin per scoop (29.6 g), with rice protein and other nutrients. Label directions: 1 scoop once daily in 8 to 10 ounces of liquid; no children's dose; ask a physician first if pregnant or nursing.
For a child, the pediatrician should choose the product and the dose.
Questions to take to your doctor
- Based on what we eat, especially dairy, eggs and fortified grains, are we likely to fall short of the riboflavin RDA?
- Do any signs such as cracks at the corners of the mouth or sore lips justify an EGRAC test or other labs?
- If I take a B-complex and a multivitamin, how much riboflavin am I getting in total, and is that amount useful?
- Given my MTHFR result, should my riboflavin intake be reviewed together with folate?
Sources
- NIH Office of Dietary Supplements. Riboflavin: Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/Riboflavin-HealthProfessional/
- Zempleni J, Galloway JR, McCormick DB. Pharmacokinetics of orally and intravenously administered riboflavin in healthy humans. Am J Clin Nutr. 1996. PubMed 8604671
- Dainty JR, et al. Quantification of the bioavailability of riboflavin from foods by use of stable-isotope labels and kinetic modeling. Am J Clin Nutr. 2007. PubMed 17556693
- Schoenen J, Jacquy J, Lenaerts M. Randomized controlled trial of high-dose riboflavin, 400 mg a day for 3 months. Neurology. 1998. PubMed 9484373
- Hoey L, McNulty H, Strain JJ. Studies of biomarker responses to intervention with riboflavin: a systematic review. Am J Clin Nutr. 2009. PubMed 19403631
- Powers HJ, et al. Correcting a marginal riboflavin deficiency improves hematologic status in young women in the United Kingdom (RIBOFEM). Am J Clin Nutr. 2011. PubMed 21525198
- McNulty H, et al. Riboflavin lowers homocysteine in individuals homozygous for the MTHFR 677C→T polymorphism. Circulation. 2006. PubMed 16380544
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease. This article is educational and is not medical advice.