Riboflavin
Vitamin B2, used as a yellow food colour and to fortify foods. An essential nutrient your body needs for energy and cell growth.
What is it?
Riboflavin is vitamin B2, a water-soluble B vitamin that occurs naturally in milk, eggs, liver, meat, fish, and leafy vegetables. As a food additive it is produced commercially by microbial fermentation, using fungi or bacteria such as Ashbya gossypii or Bacillus subtilis grown on plant-based media, or by chemical synthesis. It comes in two forms: riboflavin (E101i) and riboflavin-5-phosphate sodium (E101ii), a water-soluble salt form. Both forms are chemically identical in nutritional function.
What does it do?
In the body, riboflavin is converted into two coenzymes, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These act as electron carriers in the mitochondrial electron transport chain, enabling cells to generate energy from carbohydrates, fats and proteins. FAD is also required for the activity of methylenetetrahydrofolate reductase (MTHFR), a key enzyme in folate and one-carbon metabolism, and plays roles in metabolising iron, vitamin B6, and converting tryptophan to niacin. As a food additive, riboflavin also imparts a yellow to orange-yellow colour, though its low water solubility limits its colouring application compared with other approved dyes.
Where you will see it
Breakfast cereals (where it is added for nutritional fortification), energy drinks and vitamin-enriched beverages, processed cheese and cheese spreads, confectionery fillings, bakery mixes, instant soups and sauces, drink powders, and some meat products and snack coatings. Also found in food supplements and multivitamin preparations. On a UK label it appears as 'riboflavin', 'riboflavin-5-phosphate', 'E101', 'E101(i)', or 'E101(ii)'.
What the science says
Riboflavin and migraine prevention
High-dose riboflavin supplements (400mg per day, far above any food additive exposure) have been studied as a preventive treatment for migraine. The main randomised controlled trial found that 59% of riboflavin takers had at least 50% fewer attacks after three months, compared with 15% on placebo. The proposed mechanism is that riboflavin supports mitochondrial energy production, which is thought to be impaired in people who get migraines. This is a therapeutic supplement effect, not a concern from riboflavin in food.
Riboflavin 400mg/day reduced migraine attack frequency and headache days significantly compared with placebo over three months (59% of riboflavin takers were responders vs 15% on placebo).
A systematic review of published trials found riboflavin at high supplemental doses reduces migraine frequency, supporting its use as a low-cost prophylactic option.
Safety at food additive levels
The EFSA Panel on Food Additives and Nutrient Sources re-evaluated riboflavin and riboflavin-5-phosphate sodium in 2013 and found no concerns about genotoxicity or toxicity at the levels found in food. No numerical acceptable daily intake was set, because riboflavin is an essential nutrient at ordinary intake levels and no adverse effects were seen even at very high experimental doses. JECFA (the WHO/FAO joint committee) similarly concluded 'ADI not specified', meaning no numerical limit is considered necessary when used as intended.
EFSA concluded riboflavin (E101i) and riboflavin-5-phosphate sodium (E101ii) are unlikely to be of safety concern at currently authorised uses and use levels; no numerical ADI was set.
JECFA found riboflavin from fermentation substantially equivalent to synthetic riboflavin; genotoxicity tests were negative; NOEL in rats was 200mg/kg body weight per day; group ADI set as 'not specified'.
Riboflavin is water-soluble and the gut can only absorb a limited amount at one time; excess is rapidly excreted in urine. No tolerable upper intake level has been established because no toxic effects from food or typical supplements have been identified.
Riboflavin as a photosensitiser
Riboflavin is a known photosensitiser: when exposed to UV or blue light it can generate reactive oxygen species through two chemical pathways, causing oxidative damage to nearby proteins and fats. This property is well documented in food science, where it causes riboflavin-containing products such as milk to degrade when stored in light. It is also being explored therapeutically in eye treatment and pathogen inactivation. The photosensitising effect is relevant to food quality and to direct high-intensity light exposure to skin or eyes, not to dietary consumption of riboflavin in normal food.
Riboflavin acts as a photosensitiser via both Type I (electron transfer, protein radical formation) and Type II (singlet oxygen generation) pathways when exposed to UV or blue light, causing oxidative damage to food proteins, lipids and vitamins.
Where it stands with the regulators
Who should be careful
No population group needs to avoid riboflavin in food. Those with very rare riboflavin sensitivity or flavin-related metabolic disorders should follow medical advice. For people checking for vitamin B2 on a label, it appears as 'riboflavin', 'riboflavin-5-phosphate', or 'E101'.
The honest read
Riboflavin has been in the food supply as a colour and fortification nutrient for well over half a century. It is an essential vitamin with a clearly established biological role. Both EFSA (2013) and JECFA concluded that no numerical safe-intake limit was needed because the evidence from animal and human studies produced no adverse effects at realistic exposure levels, and because riboflavin that the body does not need is excreted in urine. The only documented high-dose effect is bright yellow urine, which occurs with supplemental doses (around 400mg/day, prescribed for migraine prevention) many times higher than any food additive exposure. At food additive levels, the established science does not point to any risk signal. The photosensitising property of riboflavin is a real chemical phenomenon but relates to food quality and direct light exposure, not to eating riboflavin-containing food.
Related additives
Common questions
Is E101 banned in the UK?
No. E101 riboflavin is approved for use in the UK under the assimilated EU Regulation 1333/2008. It appears on the UK FSA approved additives list as a permitted colour.
Does E101 cause any health effects?
No adverse health effects have been identified at the levels used in food. At very high supplemental doses (around 400mg/day, prescribed for migraine prevention), the main known effect is that urine turns bright yellow because excess riboflavin is excreted. No tolerable upper intake level has been set because no toxic effects have been found.
What foods contain E101?
Breakfast cereals, energy and vitamin-enriched drinks, processed cheese, confectionery fillings, instant soups and sauces, bakery mixes, and food supplements. It can also appear in meat products and snack coatings. On the label it reads as 'riboflavin', 'riboflavin-5-phosphate', 'E101', 'E101(i)', or 'E101(ii)'.
Is E101 vegan?
Most commercial riboflavin is produced by microbial fermentation using plant-based growth media, or by chemical synthesis, making it vegan. A small number of manufacturers extract riboflavin from animal sources such as beef liver; products labelled 'natural riboflavin' could theoretically use this route. Contacting the food manufacturer is the only way to confirm the source for a specific product.
Sources
- EFSA ANS Panel: Scientific Opinion on the re-evaluation of riboflavin (E101i) and riboflavin-5-phosphate sodium (E101ii) as food additives, EFSA Journal 11(10):3357
- JECFA: Food colour riboflavin from genetically modified Bacillus subtilis, WHO Food Additives Series 42
- UK Food Standards Agency: Approved additives and E numbers
- Schoenen J et al., Effectiveness of high-dose riboflavin in migraine prophylaxis. A randomized controlled trial, Neurology 50(2):466-470
- Thompson DF, Saluja HS. Prophylaxis of migraine headaches with riboflavin: a systematic review, Journal of Clinical Pharmacy and Therapeutics 42(4):394-403
- Cardoso DR et al., Riboflavin as a photosensitizer: effects on human health and food quality, Food and Function (RSC Publishing)
- International Association of Color Manufacturers: Riboflavins colour profile
- Vegetarian Resource Group: Riboflavin (Vitamin B-2) typically vegan
- EU Regulation (EC) No 1333/2008 on food additives (consolidated text)
- Regulation 1333/2008 Annex II: UK assimilated version
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