What riboflavin does
Riboflavin (vitamin B2) is a water-soluble B vitamin that helps convert food into energy and supports the function of other B vitamins. The NIH Office of Dietary Supplements sets the adult RDA at 1.3 mg/day for men and 1.1 mg/day for women (higher in pregnancy and lactation) [1].
No upper limit
The Food and Nutrition Board did not establish a Tolerable Upper Intake Level for riboflavin, because adverse effects from high intakes — even 400 mg/day for at least three months — have not been reported [1]. As a water-soluble vitamin, the surplus is excreted, and a high dose can turn urine a harmless bright yellow.
Food sources
Riboflavin is widespread in the food supply [1]:
- Milk, yogurt, and cheese
- Eggs and lean meats
- Fortified breakfast cereals and grains
- Almonds and mushrooms
Deficiency and who's at risk
Deficiency (ariboflavinosis) is uncommon in well-fed populations but can cause sore throat, cracks at the corners of the mouth, inflammation of the lips and tongue, and skin changes [1]. People more likely to fall short include [1]:
- Vegan or vegetarian athletes with limited dairy intake
- People who consume little or no milk and dairy
- Pregnant and lactating women with limited meat and dairy
- People with a rare riboflavin transporter disorder
Practical guidance
Most people meeting the RDA through a normal diet do not need a riboflavin supplement; it is also a standard part of any B-complex. Because there is no toxicity concern, the main point is simply ensuring adequate intake if you're in an at-risk group — bright yellow urine after a B-complex is expected and harmless.