What is the daily limit for riboflavin?

January 9, 2026 •

3 min read

A Tolerable Upper Intake Level (UL) has not been established for riboflavin, or vitamin B2, because no toxic level has been observed from food or long-term high-dose supplements. This means there is no official daily limit for riboflavin.

Quick Summary

There is no official Tolerable Upper Intake Level (UL) for riboflavin, as toxicity from dietary or supplemental intake is rare. Excess is naturally excreted through urine, but caution is advised with very high doses.

Key Points

No UL Established: No official Tolerable Upper Intake Level (UL) exists for riboflavin, as scientific data have not identified a toxic dose.
Limited Absorption: The body has a finite capacity to absorb riboflavin from a single dose, limiting the amount that can enter the bloodstream.
Rapid Excretion: Excess riboflavin is water-soluble and is rapidly excreted in the urine, preventing toxic buildup.
Benign Side Effects: The most common and harmless side effect of high-dose intake is bright yellow urine (flavinuria).
High-Dose Therapeutic Use: Doses of up to 400 mg per day have been used safely under medical supervision to help prevent migraines.
Distinguish from RDA: The lack of a UL does not negate the importance of adhering to the Recommended Dietary Allowance (RDA) for optimal nutrition.

Understanding Riboflavin: Vitamin B2

Riboflavin, also known as vitamin B2, is a water-soluble vitamin that plays a crucial role in the body's energy production. It is an essential component of two major coenzymes, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which are involved in cellular function, growth, development, and the metabolism of fats, drugs, and steroids. As a water-soluble vitamin, any excess amount that the body does not need is not stored and is instead flushed out through the urine. This unique property is the primary reason behind the vitamin's low toxicity and the lack of a formal upper intake level.

Why There Is No Tolerable Upper Intake Level (UL) for Riboflavin

The Food and Nutrition Board (FNB) at the Institute of Medicine did not establish a Tolerable Upper Intake Level (UL) for riboflavin. A UL is the maximum daily nutrient intake level that is unlikely to cause adverse health effects in almost all individuals in a population. For riboflavin, there is insufficient evidence to suggest that high intake poses a risk of toxicity. Several factors contribute to its remarkable safety profile:

Limited Absorption and Rapid Excretion

The human body has a limited capacity to absorb riboflavin from the gastrointestinal tract. Studies show that the maximum amount absorbed from a single oral dose is around 27 mg. Beyond this point, any excess is poorly absorbed and rapidly excreted in the urine. This rapid elimination mechanism prevents a toxic buildup of the vitamin in tissues and organs. While it is virtually impossible to overdose on riboflavin, some mild side effects can occur at very high doses.

Use in High-Dose Therapeutic Applications

Paradoxically, the safety of riboflavin at high doses is demonstrated by its use in certain medical treatments. For instance, high-dose riboflavin supplementation (e.g., 400 mg/day) has been studied and used under medical supervision for the prophylactic treatment of migraine headaches. This is thought to be due to its role in mitochondrial function, which is sometimes implicated in migraines. Clinical trials for this purpose have generally reported no significant adverse effects, supporting the high-tolerance profile of the vitamin.

Recommended Dietary Allowances (RDA) vs. Daily Limit

It is important not to confuse the absence of an official UL with having no recommended daily amount. The RDA is the average daily level of intake sufficient to meet the nutrient requirements of nearly all healthy individuals. These figures are determined to prevent deficiency, not to define a maximum safe limit. The specific RDA varies by age, sex, and life stage.


Life Stage	Age	Male RDA (mg/day)	Female RDA (mg/day)	Pregnancy RDA (mg/day)	Lactation RDA (mg/day)
Infants	0–6 months	0.3 (AI)	0.3 (AI)	N/A	N/A
Infants	7–12 months	0.4 (AI)	0.4 (AI)	N/A	N/A
Children	1–3 years	0.5	0.5	N/A	N/A
Children	4–8 years	0.6	0.6	N/A	N/A
Children	9–13 years	0.9	0.9	N/A	N/A
Adolescents	14–18 years	1.3	1.0	1.4	1.6
Adults	19+ years	1.3	1.1	1.4	1.6

*AI = Adequate Intake, used when an RDA cannot be determined.

Potential Effects of High Riboflavin Intake

While not toxic, some side effects have been noted with extremely high supplemental doses of riboflavin, including:

Bright yellow urine (known as flavinuria)
Mild gastrointestinal upset or diarrhea
Possible increased photosensitivity to ultraviolet radiation in theory (mostly noted in in vitro studies)

These effects are generally considered harmless and reversible upon reducing the dosage. For healthy individuals, the amount of riboflavin from a balanced diet and standard multivitamin supplements is far below levels that might cause concern. Food sources rich in riboflavin include:

Organ meats (liver, kidney)
Dairy products (milk, yogurt, cheese)
Fortified breakfast cereals and bread
Eggs
Lean beef and pork
Fish (salmon, clams)
Green leafy vegetables (spinach, kale)
Mushrooms

Conclusion

In conclusion, there is no official daily limit for riboflavin because scientific evidence does not indicate a risk of toxicity from high intakes, either from food or supplements. The vitamin's water-soluble nature ensures that any excess is efficiently excreted by the body. While mild side effects like yellow urine may occur with large supplemental doses, serious health risks are not associated with its consumption. For most people, meeting the Recommended Dietary Allowance (RDA) through a balanced diet is sufficient to prevent deficiency and ensure optimal health. For specific high-dose therapeutic uses, it is crucial to do so under the guidance of a healthcare professional. To learn more about nutrient recommendations, consult authoritative sources like the NIH Office of Dietary Supplements.

Frequently Asked Questions

An overdose of riboflavin is highly unlikely. Since it is a water-soluble vitamin, any amount the body cannot use is simply excreted through urine, which naturally prevents it from reaching toxic levels in the body.

The most common and harmless side effect of high supplemental riboflavin intake is bright yellow urine. In some cases, high doses might cause mild stomach upset, but serious adverse effects are not known.

The Recommended Dietary Allowance (RDA) for adult men is 1.3 mg per day, while for adult women it is 1.1 mg per day. Requirements increase during pregnancy (1.4 mg) and lactation (1.6 mg).

Yes, it is common for oral riboflavin supplements, especially in higher doses, to cause your urine to turn a bright, fluorescent yellow or yellow-orange color. This effect is temporary and not a cause for concern.

For most healthy people in developed countries, a balanced diet that includes dairy products, eggs, fortified grains, and lean meats provides sufficient riboflavin to meet the RDA. Dietary deficiency is rare in such populations.

Aside from minor side effects like discolored urine, there are no known toxic effects associated with high oral doses of riboflavin, even for long-term use. The limited absorption and efficient excretion prevent toxicity.

Certain groups, such as vegan athletes, pregnant and lactating women, and individuals with a rare genetic disorder called riboflavin transporter deficiency, may require higher riboflavin intake.