Last reviewed: 11 May 2026
The acidulant in cola drinks. A bone-density question, and a dental-erosion mechanism.
E338 is phosphoric acid (also called orthophosphoric acid) — the acidulant used in cola drinks and some processed foods to give them their characteristic sharp, acidic flavour and lower their pH. The EFSA acceptable daily intake is 40mg/kg body weight per day expressed as phosphorus, set as a group ADI across phosphates. Two published health questions sit on this molecule: (1) some observational studies link cola consumption to lower bone mineral density, particularly in women, though the causal mechanism is contested in the literature; and (2) like citric acid and other beverage acids, phosphoric acid erodes tooth enamel — the same dental advice as for any acidic drink applies (use a straw, rinse afterwards, don't sip slowly).
Phosphoric acid is a simple inorganic acid — three hydrogens around a central phosphate group (H₃PO₄). At the dilute concentrations used in soft drinks, it provides a sharp, clean acid taste without the citrus character of citric acid (E330), which is why cola formulators choose it: the acid backbone needs to disappear behind the caramel-and-spice flavour profile of cola, not add a fruit note. Phosphoric acid is also a more "linear" acid than citric — it doesn't buffer pH in the same way — so a cola drink ends up at a pH of around 2.5, similar in acidity to gastric juice.
On a UK ingredients list it appears as phosphoric acid, E338, or acidity regulator (E338).
Several observational studies have found an association between cola consumption (specifically cola, not other soft drinks) and lower bone mineral density. The most-cited is the Framingham Osteoporosis Study (Tucker et al., American Journal of Clinical Nutrition, 2006), which observed reduced hip bone mineral density in women drinking three or more colas a day, but not in women drinking comparable amounts of non-cola soft drinks. Because the bone-density signal showed up for cola and not for citric-acid soft drinks at similar volumes, the proposed mechanism centres on phosphoric acid disturbing calcium-phosphorus balance — high dietary phosphate intake influencing parathyroid hormone, which mobilises calcium from bone.
The causal evidence is contested. Confounding is difficult to disentangle: heavy cola drinkers tend to drink less milk, exercise less and have lower overall dietary calcium intakes. Subsequent reviews — including a 2019 systematic review in Bone Reports — find a consistent but modest association without being able to isolate phosphoric acid as the causal agent. The honest summary is that observational evidence repeatedly flags cola consumption as a marker of lower bone density in women, but the literature has not resolved how much of that is the phosphoric acid itself versus displacement of milk and other calcium sources from the diet.
The dental-erosion mechanism is well-established. Cola has a pH of around 2.5; tooth enamel begins to demineralise below pH 5.5. Regular cola consumption, especially the slow-sipping pattern common with a desk drink or a bar measure, gives the acid prolonged contact with enamel and produces measurable erosion over time. The British Dental Association advice for any acidic drink (cola, fruit juice, sports drinks, sparkling water, wine) is consistent: drink in one sitting rather than sipping over hours, rinse with plain water afterwards, use a straw to bypass the front teeth, and don't brush for at least 30 minutes after an acidic drink (brushing softened enamel accelerates erosion).
People with chronic kidney disease are advised to limit dietary phosphate (from both additives and naturally occurring sources such as dairy, meat and pulses), because impaired kidneys can't excrete excess phosphorus and elevated serum phosphate drives complications including vascular calcification and renal bone disease. This is a population-specific clinical concern handled by a renal dietitian — it is not the same situation as a person with normal kidneys. For the general UK population with healthy kidneys, dietary phosphoric acid from cola is one contributor to a total daily phosphorus intake that already includes dairy and protein foods; total phosphorus in the typical UK diet sits comfortably within the EFSA group ADI in the general case, but additive phosphate is more readily absorbed than the phosphate naturally bound up in foods, so it disproportionately raises serum phosphate spikes.
EFSA reviewed the phosphate additive group (E338, E339, E340, E341, E343 and the E450 series) in 2019 and revised the group acceptable daily intake to 40mg/kg body weight per day, expressed as phosphorus. EFSA noted that for some population groups — high consumers of soft drinks and infants on phosphate-containing formula — habitual dietary intake may approach or exceed the ADI, and recommended monitoring.
Phosphoric acid is named in the ingredients list as phosphoric acid or E338, typically near other acidity regulators. The single largest dietary source for most UK adults is cola — citric-acid soft drinks (orange, lemon, lime sodas) use E330 instead and don't carry the cola-specific bone-density observational signal. If you're watching dietary phosphate for kidney reasons, scanning ingredients for the phosphate family (E338, E339, E340, E341, E450 series) is the practical step; renal dietetics guidance covers the specifics.
UK and EU: authorised as E338. EFSA group ADI 40mg/kg body weight per day expressed as phosphorus, across the phosphate additives group (2019 re-evaluation).
United States: FDA Generally Recognized as Safe (GRAS). No equivalent ADI is set in US food law.
Scan any UK pack in NutraSafe and we surface phosphoric acid alongside the rest of the additives, so you can spot the cola acidulant — and the wider phosphate family — before it's in the trolley.
Get NutraSafe on the App StoreLast updated: 11 May 2026
Free to log up to 25 foods/day · NutraSafe Pro £3.99/month for AI Coach, allergen warning detail and full reaction history.