Phosphoric acid
A strong acid used to sharpen and preserve the sharp, tangy taste in colas and other fizzy drinks. Also controls acidity in processed foods.
High regular intake, especially from colas, is linked to lower bone mineral density and a higher risk of kidney stones. Toddlers and children who eat a lot of processed foods can exceed the phosphate safety limit when multiple phosphate additives combine.
What is it?
Phosphoric acid (also called orthophosphoric acid) is a mineral acid derived from phosphate rock. It is a clear, colourless, odourless liquid with a sharp sour taste. In food, it provides acidic sharpness and acts as a preservative against microbial growth.
What does it do?
Lowers the pH of drinks and foods, giving them a clean, sharp tartness and slowing bacterial and fungal growth. In cola, it also reacts with carbon dioxide to help hold carbonation and balances the sweetness of sugar or sweeteners. It is more shelf-stable and cheaper than citric acid for high-volume soft drink production.
Where you will see it
Most commonly in cola drinks, where it is the primary acidulant. Also in some other carbonated soft drinks, processed cheese products, jams and marmalades, canned vegetables, and certain meat products. On a label it appears as 'phosphoric acid' or 'E338'.
What the science says
Bone mineral density and cola intake
Several observational studies have found an association between high cola consumption and lower bone mineral density, particularly in women. The proposed mechanism is that cola's phosphoric acid increases urinary calcium excretion and may disturb the calcium-to-phosphorus ratio in the body. However, it is difficult to separate the effect of phosphoric acid from other features of cola drinking, such as low milk intake and high caffeine intake.
In a large observational study, women who drank cola daily had significantly lower bone mineral density at the hip compared with those who did not drink cola, regardless of calcium or vitamin D intake.
EFSA's 2019 re-evaluation noted that the bioavailability of inorganic phosphate from food additives is around 80 to 90 percent, higher than from natural food sources, and that this raises phosphorus load on the kidneys.
Kidney stones
Phosphoric acid makes urine more acidic. An acidic urinary environment promotes the formation of uric acid kidney stones and, in some people, calcium oxalate stones. Epidemiological studies have reported higher kidney stone risk in people with high cola intake, though the overall dietary pattern confounds the picture.
A prospective cohort study found that people who drank two or more cola drinks per day had a higher risk of kidney stones compared with those who drank less than one per week.
Phosphate overload and children
EFSA's 2019 group evaluation of phosphoric acid and all phosphate food additives (E338 to E452) set a group acceptable daily intake of 40 mg phosphorus per kg of body weight per day. Exposure modelling found that a proportion of toddlers and children with high processed-food consumption were at risk of exceeding this limit when the effects of multiple phosphate additives stack up. The 2019 opinion did not find evidence of harm at current mean exposure in adults.
EFSA set a group ADI of 40 mg phosphorus/kg body weight/day for phosphate food additives. High-end dietary exposure estimates in toddlers and children exceeded this ADI, raising a concern in those age groups.
Dental erosion
Phosphoric acid is corrosive to tooth enamel at the concentrations used in cola drinks, which typically have a pH of around 2.4. Regular exposure of enamel to this pH causes measurable erosion over time. This is a well-established direct effect, separate from sugar-driven decay.
Laboratory studies measuring enamel hardness before and after cola exposure consistently show surface softening and erosion at cola pH levels, with phosphoric acid identified as the primary causative agent.
Chronic kidney disease
People with chronic kidney disease already have impaired phosphate excretion. Dietary phosphate from food additives is absorbed at a much higher rate than phosphate from natural food sources, and nephrologists routinely advise CKD patients to limit foods containing added phosphates, including colas.
EFSA noted that inorganic phosphate from additives is approximately 80 to 90 percent bioavailable, compared with 40 to 60 percent from natural food. In people with impaired kidney function, this elevated absorption meaningfully increases phosphate load.
Where it stands with the regulators
Who should be careful
People with chronic kidney disease should limit foods with added phosphates because the kidneys cannot clear excess phosphate. Children who eat a lot of processed food may exceed the phosphate group limit when several phosphate additives accumulate across their diet. People prone to kidney stones may want to reduce cola intake. Look for 'phosphoric acid' or 'E338' on the label.
The honest read
The science distinguishes between phosphate naturally present in foods (absorbed at 40 to 60 percent) and phosphate from food additives such as E338 (absorbed at 80 to 90 percent). Regulators treat them separately for that reason. The EFSA 2019 re-evaluation is the most thorough review to date and found the additive acceptable at current mean exposure in adults, while raising a specific concern about cumulative phosphate intake in young children eating highly processed diets. The bone density literature is largely observational and tangled with confounders: people who drink a lot of cola tend to drink less milk and more caffeine, both of which affect bone independently. The kidney-stone association is more consistent. For most adults the practical question is total phosphate load across a whole processed-food diet, not E338 in isolation.
Related additives
Common questions
Is E338 banned in the UK?
No. Phosphoric acid is an approved food additive in the UK under the assimilated EU Regulation 1333/2008, authorised across a range of food categories including soft drinks.
Does the phosphoric acid in cola weaken your bones?
Observational studies have found an association between regular cola drinking and lower bone mineral density, particularly in women. The picture is complicated by the fact that heavy cola drinkers often drink less milk and more caffeine, both of which also affect bone. A causal link specifically to phosphoric acid has not been established in humans, but the concern is not dismissed by regulators.
What foods contain E338?
Cola drinks are by far the largest source. E338 is also used in some other carbonated drinks, processed cheese, jams, canned vegetables and certain meat products. Check the ingredients list for 'phosphoric acid' or 'E338'.
Is E338 vegan?
Yes. Phosphoric acid is a mineral acid derived from inorganic phosphate rock and contains no animal-derived ingredients.
Sources
- UK FSA Register of Food Additive Authorisations: E338 Phosphoric acid
- EFSA 2019 re-evaluation of phosphoric acid and phosphates (E338-341, E343, E450-452), EFSA Journal 5674
- Tucker et al. (2006) Colas, but not other carbonated beverages, are associated with low bone mineral density in older women. American Journal of Clinical Nutrition
- Curhan et al. (1996) Prospective study of beverage use and risk of kidney stones. Epidemiology
- EFSA press release: EFSA issues new advice on phosphates (June 2019)
- UK FSA Approved additives and E numbers
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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