E-numbers / Other additives / E101
also: Vitamin B2 · Lactoflavin · Riboflavin (i) · E101(i)
Vitamin B2, which your cells need to make energy, used to colour food yellow and to add the vitamin to cereals. Large doses turn urine bright yellow.
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Maize, sugar, salt, barley malt extract, niacin, iron, pantothenic acid (B5), vitamin B6, thiamin (B1), riboflavin, folic acid, vitamin D, vitamin B12
Riboflavin is vitamin B2, a vitamin found naturally in milk, eggs, liver, meat, fish and leafy vegetables.
728
of the 43,325 UK supermarket foods we checked declare E101 in their ingredients
That is 1.7%, counted by its code or its name. The count includes every form of E101 (E101a).
Counted by NutraSafe from UK supermarket ingredient lists, September 2026. How we counted
Riboflavin is vitamin B2, a vitamin found naturally in milk, eggs, liver, meat, fish and leafy vegetables. For food it is mostly made by fermentation, with fungi or bacteria grown on plant-based feed, or made chemically. It comes as riboflavin (E101i) or riboflavin-5-phosphate sodium (E101ii), a form that dissolves more easily in water.
In the body, riboflavin is turned into two helper molecules that cells need to get energy from carbohydrates, fats and proteins. They are also needed to use folate, iron and vitamin B6. As an additive, it gives food a yellow to orange-yellow colour, though it does not dissolve well, which limits how much it is used as a colour.
Breakfast cereals (where it is added as a vitamin), energy drinks and vitamin drinks, processed cheese and cheese spreads, sweet fillings, baking mixes, instant soups and sauces, drink powders, and some meat products and snack coatings. Also in supplements and multivitamins. UK labels call it riboflavin, riboflavin-5-phosphate, E101, E101(i) or E101(ii).
Riboflavin supplements at 400mg a day, far more than any food additive supplies, have been tested for preventing migraine. In the main randomised trial, 59% of people taking riboflavin had at least half as many attacks after three months, against 15% on a dummy pill. One idea is that it helps the cells' energy production, which may work less well in people who get migraines.
Riboflavin at 400mg a day clearly cut migraine attacks and headache days compared with a dummy pill over three months. 59% of those taking it responded, against 15% on the dummy pill.
A review of published trials found high-dose riboflavin supplements reduce how often migraines happen.
European reviewers looked at both forms of riboflavin in 2013 and found no DNA-damage or toxicity issue at the amounts in food. They set no numerical daily limit, because riboflavin is a vitamin people need and no harm was seen even at very high test doses. The international committee reached the same view. The body absorbs only a limited amount at once and passes the rest out in urine.
Reviewers judged riboflavin (E101i) and riboflavin-5-phosphate sodium (E101ii) unlikely to be a safety issue at current uses and levels, and set no numerical daily limit.
The international committee found riboflavin made by fermentation equivalent to the chemically made kind, found DNA-damage tests negative, noted no effect in rats at 200mg per kg of body weight a day, and set the daily limit as not specified.
The gut absorbs only a limited amount of riboflavin at once, and the excess leaves quickly in urine. No upper intake limit has been set, because no toxic effects from food or normal supplements have been found.
When riboflavin is exposed to UV or blue light it produces reactive oxygen, which damages nearby proteins and fats. That is why milk kept in the light loses flavour and vitamins. It matters for food quality and for strong light on skin or eyes, not for eating food that contains riboflavin.
In UV or blue light, riboflavin produces reactive oxygen by two chemical routes, damaging proteins, fats and vitamins in food.
Daily limit. None set, by European reviewers (2013) or the international committee.
No group is told to avoid riboflavin in food. People with rare disorders of how the body handles flavins should follow medical advice. On a label it appears as riboflavin, riboflavin-5-phosphate or E101.
Riboflavin has been used as a colour and added vitamin for more than half a century, and it is a vitamin the body needs. European reviewers and the international committee set no numerical limit, because studies in animals and people found no harm at realistic amounts and the body passes out what it does not need. The one well-known effect of high doses, around 400mg a day as used for migraine, is bright yellow urine. Its reaction to light is real chemistry, but it concerns food quality and strong light, not eating it.
No. Riboflavin is approved in the UK and is on the Food Standards Agency's list as a permitted colour.
Reviewers have not found harm at the amounts used in food. At very high supplement doses, around 400mg a day as used to prevent migraine, the main known effect is bright yellow urine, as the body passes out the excess. No upper intake limit has been set, because no toxic effects have been found.
Breakfast cereals, energy and vitamin drinks, processed cheese, sweet fillings, instant soups and sauces, baking mixes and supplements. It can also appear in meat products and snack coatings. Labels call it riboflavin, riboflavin-5-phosphate, E101, E101(i) or E101(ii).
Usually. Most commercial riboflavin is made by fermentation on plant-based feed or chemically. A few makers extract it from animal sources such as liver, so a product labelled "natural riboflavin" could in theory use that route. Ask the maker if it matters to you.
Last reviewed: 20 June 2026
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