How the body handles it
After ingestion, intestinal enzymes rapidly convert riboflavin-5'-phosphate into free riboflavin, which the body absorbs and uses as vitamin B2. Excess riboflavin is excreted in urine, causing it to appear bright yellow at higher intakes. The body's ability to absorb riboflavin saturates at higher doses, limiting how much can accumulate from any single exposure.
Riboflavin-5'-phosphate sodium is rapidly dephosphorylated to free riboflavin in the intestinal mucosa and then metabolised through standard vitamin B2 pathways, with no unique toxic properties introduced by the phosphate salt form.
2013Regulatory reviewEFSA ANS Panel, Scientific Opinion on the re-evaluation of riboflavin (E101(i)) and riboflavin-5'-phosphate sodium (E101(ii)) as food additives, EFSA Journal 11(10):3357
Data gaps identified by regulators
When EFSA re-evaluated this additive in 2013, it noted that long-term carcinogenicity studies and reproductive and developmental toxicity studies were absent from the database. Because of those gaps, EFSA considered it inappropriate to set a numerical ADI for riboflavin used as a food additive, despite concluding that use at currently authorised levels is unlikely to raise concern. This is a procedural position reflecting incomplete data, not an identified hazard.
Due to the absence of carcinogenicity and chronic toxicity studies, and the lack of relevant reproductive and developmental toxicity studies, the EFSA Panel considered it not appropriate to allocate an ADI for riboflavin food additives, while noting the database was insufficient to assess potential effects of high intakes from all combined sources.
2013Regulatory reviewEFSA ANS Panel, Scientific Opinion on the re-evaluation of riboflavin (E101(i)) and riboflavin-5'-phosphate sodium (E101(ii)) as food additives, EFSA Journal 11(10):3357
JECFA at its 92nd meeting (2021) established a group ADI of 'not specified' for riboflavin and riboflavin-5'-phosphate, withdrawing the previous numerical group ADI of 0-0.5 mg/kg body weight, indicating the committee considered a numerical limit unnecessary at intended use levels.
2021RegulatoryJECFA, 92nd meeting, WHO/FAO
Genotoxicity
Laboratory studies found no evidence that riboflavin or its phosphate form damages DNA. EFSA's 2013 review of available in vitro and in vivo data concluded that neither substance raises concern for genotoxicity.
Riboflavin and riboflavin-5'-phosphate do not raise concern with respect to genotoxicity based on available in vitro and in vivo data.
2013Lab + animalEFSA ANS Panel, Scientific Opinion on the re-evaluation of riboflavin (E101(i)) and riboflavin-5'-phosphate sodium (E101(ii)) as food additives, EFSA Journal 11(10):3357
Rare allergy
A small number of case reports describe allergy to riboflavin, including one case of anaphylaxis in an adolescent after exposure from both a soft drink and a multivitamin. These reactions are uncommon and not a general population risk, but anyone who has experienced a reaction to riboflavin or vitamin B2 supplements should check ingredient labels carefully.
A case report described recurrent anaphylaxis in a 15-year-old boy linked to riboflavin in a soft drink and a multivitamin, confirmed by positive intradermal skin tests; this was described as the first reported case of anaphylaxis to riboflavin at the time.
2001ObservationalAnnals of Allergy, Asthma and Immunology, vol. 87, pp. 430-433
