Vitamin C
The same vitamin C found naturally in fruit and vegetables, added to food to slow oxidation, prevent browning, and preserve colour.
What is it?
Ascorbic acid is a water-soluble vitamin that occurs naturally in citrus fruit, berries, and green vegetables. When used as a food additive it is either extracted from plant sources or synthesised from glucose, typically via the Reichstein or Gluconobacter fermentation process. The result is chemically identical to the vitamin C in food.
What does it do?
Ascorbic acid acts as an antioxidant by donating electrons to reactive oxygen species before they can oxidise fats, pigments, or flavour compounds. It effectively sacrifices itself to preserve other molecules. In dough, it also acts as a flour-treatment agent: it oxidises briefly during mixing, strengthening gluten networks so bread rises more evenly.
Where you will see it
Fruit juices, squashes, and soft drinks (to maintain colour and flavour); cured and processed meats (slows fat rancidity and helps fix the pink colour from nitrites); jams and preserves; tinned and frozen fruit; breakfast cereals; baby foods; bread and baked goods (as a dough improver). On a label it appears as 'ascorbic acid', 'L-ascorbic acid', or 'E300'.
What the science says
Role as an essential vitamin at food additive levels
The amount of ascorbic acid added as a food additive is generally small relative to the reference nutrient intake of 40mg per day for adults in the UK (SACN/COMA). At those levels it contributes to normal vitamin C intake rather than representing an unusual exposure. The body excretes any excess in urine once plasma is saturated, typically above around 200mg per day.
The UK reference nutrient intake for vitamin C is 40mg per day for adults; amounts added as a food additive fall well within normal dietary ranges.
High-dose supplementation and kidney stones
At gram-level supplemental doses (not food-additive quantities), ascorbic acid is partly metabolised to oxalate, and very high intakes have been associated with an increased risk of kidney stones in people predisposed to them. The NHS advises keeping supplement doses below 1000mg per day to avoid this. Food-additive quantities are orders of magnitude lower and do not carry this risk for the general population.
Supplemental vitamin C above 1000mg per day can raise urinary oxalate levels and increase the risk of oxalate kidney stones, particularly in those with a prior history.
The European Food Safety Authority set a tolerable upper intake level of 1000mg per day from all sources combined, based on the risk of gastrointestinal effects and oxalate formation at higher doses.
Interaction with sodium benzoate (E211) in acidic drinks
When ascorbic acid is present alongside sodium benzoate in acidic, low-oxygen conditions (common in fizzy drinks), the two can react to form small amounts of benzene, a known human carcinogen. UK and EU regulations do not prohibit the combination, but the Food Standards Agency and the food industry have worked with manufacturers to reformulate drinks where benzene levels above 10 micrograms per litre were detected. The concern here is with the co-additive E211, not with E300 alone.
Benzene can form in soft drinks containing both benzoic acid (E210/E211) and ascorbic acid (E300) under heat and light exposure; the FSA has monitored benzene levels in UK soft drinks and worked with industry to reduce them.
Benzene is classified as a Group 1 human carcinogen (sufficient evidence of carcinogenicity in humans). Benzene was first classified Group 1 in IARC Monograph Volume 29 (1982) and most recently re-evaluated in Volume 120 (2018).
Where it stands with the regulators
Who should be careful
People with a history of kidney stones (particularly calcium oxalate stones) may be advised by their doctor to limit high-dose vitamin C supplements, though food-additive quantities are not implicated. People avoiding E211 (sodium benzoate) in acidic drinks will incidentally also avoid the combination that can form benzene. Look for 'ascorbic acid' or 'E300' alongside 'sodium benzoate' or 'E211' on the same label.
The honest read
E300 is the same molecule as the vitamin C in an orange. It is one of the most extensively studied compounds in human nutrition, with decades of clinical and epidemiological research. The kidney stone signal exists only at gram-level supplement doses, far above anything encountered from food additives. The one genuine complexity is not about E300 itself but about what it can do when combined with sodium benzoate preservatives in acidic drinks: that reaction can produce trace benzene. The FSA investigated this in the mid-2000s and most manufacturers reformulated. Check the label if you drink a lot of fizzy drinks and want to avoid the combination.
Related additives
Common questions
Is E300 banned in the UK?
No. E300 (ascorbic acid) is approved for use as a food additive in the UK and EU. It appears on the UK FSA approved-additives list and is authorised under assimilated EU Regulation 1333/2008.
Can E300 form benzene in drinks?
E300 can react with sodium benzoate (E211) in acidic, low-oxygen conditions to form small amounts of benzene. The FSA found elevated benzene in some UK soft drinks in 2006 and worked with manufacturers to reduce them. The concern only applies when E300 and E211 appear together on the same label.
What foods contain E300?
Fruit juices, soft drinks, jams, processed and cured meats, tinned fruit, breakfast cereals, bread, and baby foods commonly contain E300. It appears on labels as 'ascorbic acid', 'L-ascorbic acid', or 'E300'.
Is E300 vegan?
Yes. Ascorbic acid used as a food additive is produced by fermenting plant-derived glucose or by synthesis from glucose. It does not involve animal products and is suitable for vegans.
Sources
- UK FSA Approved Additives and E Numbers
- EU Regulation 1333/2008 on food additives (Annex II)
- EFSA Panel on Dietetic Products, Nutrition and Allergies: tolerable upper intake levels for vitamins and minerals
- FSA Survey of benzene in soft drinks (2006)
- IARC Monographs on the Identification of Carcinogenic Hazards to Humans, Volume 120: Benzene (2018)
- IARC Monographs Volume 29: Benzene (first Group 1 classification, 1982)
- NHS: Vitamins and minerals - Vitamin C
Aaron Keen is the founder of NutraSafe. He researches and writes every additive entry himself, from the primary sources. About the research →
This is a guide, not medical advice. If an additive affects you, speak to your GP or a dietitian.
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