Also known as: Riboflavin, Riboflavin-5-phosphate, R5P, Vitamin G
VitaminsStrong evidence
A water-soluble vitamin that forms the backbone of two coenzymes used throughout energy metabolism. Also the reason your urine turns bright yellow after taking a multivitamin.
Typical dose
1.0–100.0 mg per day
With food; any time of day
What it is
Riboflavin is a water-soluble vitamin, named from the Latin for yellow because of its intense colour. That colour is not incidental — it is also used as a food colouring, listed as E101.
Good sources include dairy, eggs, liver, almonds and green vegetables. It is notably sensitive to light, which is why milk in glass bottles loses riboflavin and why supplements are usually in opaque packaging.
The bright yellow urine that follows a B-complex or multivitamin is riboflavin being excreted, and it is completely harmless. It is also a useful signal: it tells you the tablet dissolved and was absorbed. Riboflavin-5-phosphate is the active form and is marketed as better absorbed, though the evidence for a practical difference is limited.
How it works
Riboflavin is converted into two coenzymes, FAD and FMN, which act as electron carriers in a very large number of reactions, including those of the electron transport chain that generates most of the body's ATP.
It is also required for the enzyme that regenerates glutathione, which links riboflavin status to antioxidant capacity in a way that is often overlooked.
Riboflavin is additionally needed to activate vitamin B6 and to convert folate into its usable forms, meaning poor riboflavin status can create functional shortfalls in other B vitamins even when their intake looks adequate.
What the evidence shows
Riboflavin's essentiality is well established, and shortfall is uncommon in the UK given how much comes from dairy, though intake can be marginal in people who avoid dairy without replacing it.
There is a body of research on high-dose riboflavin and the frequency of recurrent headaches, with several trials reporting reductions at doses far above nutritional requirement. This is one of the few areas where a B vitamin at pharmacological doses has shown a specific effect, and it is worth knowing about even though it sits outside the sports nutrition framing.
For exercise performance or energy in people with adequate status, there is no meaningful evidence of benefit. Riboflavin supports energy metabolism, but supporting it and enhancing it are different things.
Dosing
Reference intakes are around 1.1-1.3 mg daily, which most UK diets cover through dairy alone.
Supplements commonly supply 25-100 mg. The research on headache frequency used considerably higher doses, in the region of 400 mg daily over several months, and anyone considering that should be doing so with medical guidance rather than off a label.
Absorption is limited per dose, so very large single amounts are largely excreted. Take with food. Expect bright yellow urine within hours — it is riboflavin doing exactly what it should.
At a glance
Common forms
Riboflavin, Riboflavin-5-phosphate (R5P), Within B-complex, Within multivitamins
Half-life / duration
Excess cleared in urine within hours; body stores are limited
Timing
With food; any time of day
Competition status
Permitted — not on the WADA Prohibited List
Category
Vitamins
Safety and side effects
Riboflavin has an excellent safety record. No tolerable upper intake level has been established, since absorption is limited and excess is efficiently excreted.
The bright yellow urine is the only universal effect and is entirely harmless. Occasional digestive upset is reported at very high doses.
Speak to your doctor before use if you take regular medication, as some medicines affect riboflavin status.
Who should avoid it
Speak to your doctor before use if you take regular medication or are under medical care. Expect harmless bright yellow urine. No significant interactions established at ordinary supplemental doses.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
