Phosphoric Acid

Phosphoric acid (E338) is a mineral acid widely used in the food and beverage industry as an acidity regulator, flavouring agent, and pH adjuster. It is best known as an ingredient in cola-type soft drinks, where it provides the characteristic sharp, tangy note that distinguishes cola flavor from other carbonated beverages. As a clear, colourless, syrupy liquid or crystalline solid, it is highly water-soluble and non-volatile under normal food-processing conditions.

Food-grade phosphoric acid is produced industrially by the wet-acid or thermal (furnace) process from phosphate rock. The thermal route yields a higher-purity product that meets food and pharmaceutical standards. Its use is tightly regulated by food safety authorities worldwide, each of which has established an Acceptable Daily Intake (ADI) or 'not specified' designation based on decades of toxicological data.

Phosphoric acid contributes phosphate ions when ingested, joining the large pool of dietary phosphorus obtained from foods such as dairy, meat, and legumes. At moderate dietary intakes this is not considered harmful for healthy individuals; however, research continues into whether chronically high phosphate intake—particularly from additive sources—may adversely affect bone mineral density, cardiovascular function, or kidney health in susceptible populations.

Public discourse around phosphoric acid has at times been disproportionate to the scientific evidence, with some sources conflating industrial-concentration acid hazards with the far-lower concentrations present in beverages. This entry presents the current scientific and regulatory consensus, notes areas of genuine uncertainty, and distinguishes well-supported conclusions from emerging or contested findings.

Phosphoric acid (H₃PO₄) is a triprotic inorganic oxoacid belonging to the phosphorus oxyacid family. Its central phosphorus atom (oxidation state +5) is tetrahedrally coordinated by four oxygen atoms: one double-bonded phosphoryl oxygen (P=O) and three hydroxyl groups (P–OH). This arrangement gives the molecule three ionisable protons with successive pKa values of approximately 2.15, 7.20, and 12.35, making it a weak-to-moderate acid at the first dissociation step and very weak at the second and third. In aqueous food systems at typical use-pH, phosphoric acid exists primarily as a mixture of the undissociated form (H₃PO₄) and the dihydrogen phosphate anion (H₂PO₄⁻). This stepwise dissociation behavior provides useful buffering capacity in acidic food and beverage matrices. Phosphoric acid is closely related to other food-relevant phosphate salts—sodium, potassium, and calcium phosphates—which are derived from the same parent acid by progressive neutralisation.

Two principal industrial routes exist for manufacturing phosphoric acid. The wet-process route treats phosphate rock (primarily fluorapatite, Ca₅(PO₄)₃F) with sulfuric acid, producing phosphoric acid and calcium sulfate (gypsum) as a by-product. Wet-process acid typically contains impurities such as fluorides, heavy metals, and organic matter and requires extensive purification—including solvent extraction, activated-carbon treatment, and ion-exchange steps—before it can meet food-grade specifications. The thermal (furnace) process produces higher-purity acid: elemental phosphorus, obtained by reducing phosphate rock with coke and silica in an electric arc furnace, is burned in air to form phosphorus pentoxide (P₂O₅), which is then hydrated to yield food- and pharmaceutical-grade H₃PO₄ (typically ≥75–85% concentration). Food-grade phosphoric acid must conform to strict purity specifications, including limits on arsenic, lead, fluoride, and other contaminants, as set out by bodies such as the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and the Food Chemicals Codex (FCC).

Phosphoric acid was first isolated and characterised in the early 18th century; the Swedish chemist Carl Wilhelm Scheele demonstrated its presence in bone ash around 1770–1780. Johann Gottlieb Gahn and others subsequently established its elemental composition. Industrial-scale production began in the mid-19th century alongside the growth of the fertiliser industry, which remains the dominant consumer of phosphoric acid globally. Its introduction into food and beverage manufacturing is closely linked to the history of carbonated soft drinks: Coca-Cola's formula, developed in 1886 by John Stith Pemberton, incorporated phosphoric acid to balance sweetness and deliver tartness, and many cola competitors adopted the same approach. By the early 20th century, food-grade phosphoric acid was a standardized commercial product. JECFA first evaluated phosphoric acid and phosphate salts in 1961, and subsequent reviews have consistently maintained a 'not specified' ADI for food-grade phosphate additives used according to Good Manufacturing Practice, indicating low acute toxicological concern. The 1980s and 1990s saw growing research into dietary phosphate and bone health, and early-2000s epidemiological studies on cola consumption and bone density reinvigorated scientific and media interest in the ingredient.

• Acidity regulation: Adjusts and stabilises pH in soft drinks, jams, jellies, and processed foods, ensuring consistent flavor and inhibiting microbial growth.
• Flavor contribution: Provides the characteristic sharp, clean tartness of cola beverages that citric or other organic acids do not fully replicate.
• Preservative synergy: Low pH created by phosphoric acid enhances the effectiveness of other preservatives and reduces spoilage organism viability.
• Chelating / sequestrant activity: Binds metal ions that would otherwise catalyse oxidative rancidity or color degradation in food products.
• Leavening acid: Used in combination with sodium bicarbonate in some baking powders and self-raising flours as a fast-acting leavening acid (though more commonly as its calcium or sodium salt).
• Processing aid: Employed to adjust pH during sugar refining, starch processing, and edible oil refining, then removed or reduced to permitted residual levels.
• Cost-effectiveness: Compared with citric or malic acid, phosphoric acid delivers equivalent acidification at lower cost per unit, a significant factor for high-volume beverage production.

Phosphate as an essential nutrient: Phosphoric acid contributes inorganic phosphate to the diet. Phosphorus is an essential mineral required for bone and tooth mineralisation (approximately 85% of body phosphorus resides in bone as hydroxyapatite), energy metabolism (ATP synthesis), cell membrane integrity (phospholipids), and intracellular signaling. In this narrow sense, phosphoric acid in food provides a bioavailable source of dietary phosphorus.

Dental erosion offset at population level: At sub-threshold concentrations used in beverages, there is no established direct health benefit from phosphoric acid itself beyond its nutritional phosphate contribution. Any benefit is primarily attributable to the phosphate ion, not the acid per se.

Note on evidence quality: No clinical or dietary intervention studies have been conducted specifically to evaluate health benefits of phosphoric acid as a food additive. Nutritional benefits of phosphorus are well-established from broader dietary research, but additive-specific benefits are not independently documented.

Dental erosion (established): Acidic beverages, including cola drinks containing phosphoric acid (pH ~2.5–3.0), are well-documented contributors to dental erosion (erosive tooth wear). Repeated, prolonged contact of acidic beverages with tooth enamel demineralises the hydroxyapatite surface. This is the most consistently documented adverse effect at typical consumer exposure levels and is considered an established risk by dental and regulatory bodies. The risk is related to frequency and pattern of consumption, not to phosphoric acid specifically versus other food acids.

Bone mineral density and fracture risk (limited evidence, ongoing research): Several observational studies, including a widely cited 2006 cross-sectional study by Tucker et al. in the American Journal of Clinical Nutrition, found associations between cola consumption and lower bone mineral density in women. The proposed mechanism involves displacement of calcium-rich beverages and possibly an unfavourable calcium-to-phosphorus dietary ratio. However, meta-analyses and systematic reviews have not established that phosphoric acid itself, independent of overall diet and lifestyle, causes clinically significant bone loss. Evidence is currently characterised as limited and inconsistent.

Kidney function (ongoing research): Higher dietary phosphate intake has been associated in some observational studies with markers of kidney disease progression in individuals with chronic kidney disease (CKD). In healthy individuals, kidneys efficiently regulate phosphate excretion; however, individuals with CKD, hypoparathyroidism, or other phosphate-handling disorders may be at risk from excessive phosphate intake including from food additives. The distinction between organic (naturally occurring) and inorganic (additive) phosphate bioavailability is an active area of research.

Cardiovascular associations (ongoing research): Elevated serum phosphate within or above the normal range has been associated epidemiologically with cardiovascular events in general-population cohorts. Whether additive phosphate intake contributes meaningfully to serum phosphate levels in healthy individuals is not established.

Corrosivity at high concentrations (established, industrial context): Concentrated phosphoric acid (≥75%) is corrosive to skin, eyes, and mucous membranes. This risk is occupational and industrial, not relevant to food-grade concentrations in finished products.

ADI (JECFA/Codex): JECFA has assigned an ADI of 'not specified' to phosphoric acid and phosphate salts (as a group, expressed as phosphorus), indicating that available toxicological data do not identify a safety concern at levels used in food under Good Manufacturing Practice. This designation does not mean unlimited consumption is recommended; it reflects that no specific numerical limit is considered necessary for the general population.

Dietary Reference Intakes (DRI) for phosphorus (USA/Canada): The Recommended Dietary Allowance (RDA) for phosphorus is 700 mg/day for adults (≥19 years). The Tolerable Upper Intake Level (UL) is 4,000 mg/day for adults aged 19–70 and 3,000 mg/day for those over 70. Adolescents (9–18 years) have a UL of 4,000 mg/day. These ULs encompass all dietary and additive phosphate sources combined.

Children: No specific ADI restriction exists for children; however, the UL for phosphorus is lower in young children (1–3 years: 3,000 mg/day; 4–8 years: 3,000 mg/day), and regulatory guidance (particularly EFSA for infant formula) establishes strict upper limits for phosphate additives in foods intended for infants.

Individuals with kidney disease: Phosphate restriction is a standard clinical recommendation for patients with advanced CKD or on dialysis. These individuals should monitor total dietary phosphate, including additive sources.

Pregnancy: No specific restriction beyond standard dietary phosphate guidance; the RDA during pregnancy is 700 mg/day for adults.

The scientific literature on phosphoric acid as a food additive spans nutritional biochemistry, dental science, nephrology, and cardiovascular epidemiology. Dental erosion is the best-evidenced adverse effect at consumer exposure levels. Systematic reviews published in Caries Research and the Journal of Dentistry consistently confirm that frequent consumption of acidic beverages—regardless of whether the acid is phosphoric, citric, or carbonic—is a leading cause of erosive tooth wear. Critically, however, the erosive potential of phosphoric acid is considered somewhat lower than that of citric acid at equivalent pH, partly due to phosphate's buffering capacity on enamel surfaces.

The bone health question gained prominence following Tucker et al. (2006, AJCN), which found lower femoral bone mineral density in women consuming ≥3 cola drinks per week. Subsequent prospective studies and meta-analyses have produced inconsistent results, with some finding no independent effect of cola after controlling for calcium and vitamin D intake, physical activity, and total diet. A 2014 systematic review in Osteoporosis International concluded that evidence for a causal link between cola consumption and fracture risk was insufficient. EFSA's 2019 re-evaluation of phosphate additives acknowledged potential concern at high aggregate phosphate intake but noted substantial uncertainties in the evidence base.

In renal physiology, research by Noori et al. (2010, Clinical Journal of the American Society of Nephrology) and others has highlighted that inorganic phosphate from food additives may be more readily absorbed (up to 100% bioavailability) than organic phosphate from naturally occurring food sources (40–60% bioavailability). This distinction has informed clinical recommendations for CKD patients but has not yet led to changes in additive-specific regulatory limits for the general population. Cardiovascular research, including work by Dhingra et al. (2007, Circulation) on soft drink consumption and metabolic syndrome, faces well-recognized confounding challenges inherent in dietary epidemiology. EFSA's 2019 group ADI of 40 mg/kg body weight per day (as phosphorus) represents a significant regulatory development, though the authority noted that current estimated intakes from phosphate additives alone are generally below this level in most European population groups.

Phosphoric acid has been subject to recurring media attention and advocacy campaigns, particularly in the context of carbonated soft drinks. A number of popular claims circulate online, including that cola beverages dissolve bone, teeth, or metal, often supported by dramatic but methodologically uncontrolled demonstrations (e.g., submerging a tooth or nail in undiluted cola for extended periods). These demonstrations do not reflect physiological exposure conditions—saliva, normal food intake, and oral clearance substantially mitigate acid contact time—and systematically overstate risk at realistic consumption patterns.

A persistent misconception conflates the industrial hazards of concentrated phosphoric acid (a corrosive substance at ≥75% concentration) with the safe, highly diluted concentrations present in finished food products (typically 0.05–0.08% in cola). These are toxicologically distinct situations. Critics of cola companies have also argued that the industry has lobbied against regulatory restrictions on phosphate additives; while documented industry engagement with regulatory processes is normal and transparent in most jurisdictions, claims of undue influence on scientific conclusions require specific evidence and should not be assumed.

The EFSA 2019 re-evaluation attracted media attention for establishing a numerical group ADI for phosphates where JECFA had maintained 'not specified' status. Some reporting characterised this as a finding of harm; in reality, EFSA's conclusion was that while current intakes are likely below the new ADI for most consumers, accumulation from multiple additive sources warrants monitoring—a precautionary, not alarming, position. Responsible science communication requires accurately conveying this distinction between a regulatory refinement and a public health crisis.

The environmental footprint of phosphoric acid is most significant at the mining and primary production stage. Phosphate rock is a finite, non-renewable mineral resource; at current extraction rates, economically accessible reserves are projected to face increasing scarcity over coming decades, raising long-term concerns about phosphorus sustainability across agriculture and industry. Phosphate rock mining generates large quantities of phosphogypsum as a by-product, which contains low levels of naturally occurring radioactive materials (NORM) and fluoride; its disposal and potential reuse are active environmental policy issues in mining regions such as Florida (USA), Morocco, and China.

Within the food and beverage sector, phosphoric acid's environmental impact is relatively modest compared with agricultural ingredients. However, phosphate-laden wastewater from food processing facilities can contribute to eutrophication of receiving water bodies if not properly treated, as phosphorus is a primary limiting nutrient for algal growth. Food-grade manufacturing facilities are subject to wastewater treatment regulations in most jurisdictions that limit phosphorus discharge. Life-cycle assessment data specific to food-grade phosphoric acid production are not widely published, but the thermal-process route is more energy-intensive than wet-process production due to electric arc furnace requirements.

Workers involved in the manufacture, handling, and transport of concentrated phosphoric acid (typically 75–85% solutions) face risks of chemical burns to skin, eyes, and respiratory mucous membranes. At high concentrations, phosphoric acid is classified as a corrosive substance under the GHS (Globally Harmonized System of Classification and Labeling of Chemicals). Regulatory agencies including OSHA (USA) and the European Chemicals Agency (ECHA) have established occupational exposure limits (OELs) and require appropriate personal protective equipment (PPE), including acid-resistant gloves, eye protection, and in misting scenarios, respiratory protection.

In food and beverage manufacturing settings, workers typically handle phosphoric acid as a dilute solution during beverage formulation. At these working concentrations the corrosivity risk is substantially reduced, though good industrial hygiene practices—including splash guards, eye wash stations, and appropriate PPE—remain standard requirements. Chronic low-level occupational inhalation of phosphoric acid mist has been studied; animal data suggest potential respiratory irritation, but human occupational epidemiology data are limited. The American Conference of Governmental Industrial Hygienists (ACGIH) has established a Threshold Limit Value–Ceiling (TLV-C) of 1 mg/m³ for phosphoric acid mist.

Preclinical animal studies have informed the toxicological database underpinning regulatory decisions on phosphoric acid and phosphate additives. Subchronic and chronic feeding studies in rodents at high dietary phosphate levels have demonstrated adverse effects on the kidneys (including tubular calcification and nephrocalcinosis) and on calcium-phosphorus homeostasis, particularly when dietary calcium is concurrently low. These effects are dose-dependent and typically occur at intakes far exceeding estimated human dietary exposure from food additives. Long-term high-phosphate diets in rat models have been associated with accelerated aging phenotypes and reduced lifespan in some experimental protocols, though the mechanistic and extrapolation relevance to human health at normal dietary phosphate levels remains a subject of research. Genotoxicity studies (Ames test, chromosomal aberration assays) have not demonstrated mutagenic or clastogenic activity for food-grade phosphoric acid. Reproductive and developmental toxicity studies in animals have not revealed teratogenic effects at relevant exposure levels. JECFA reviewed the full animal toxicology database across multiple evaluations and concluded that the data support the existing safety designations for food-grade use.

Human studies on phosphoric acid as a food additive are predominantly observational (cross-sectional, cohort, and case-control designs) rather than controlled intervention trials, reflecting the practical and ethical challenges of isolating a single dietary acid. Key areas of human research include:

Dental erosion: Clinical studies and systematic reviews confirm that frequent acidic beverage consumption—across acid types—is strongly associated with erosive tooth wear. Laboratory enamel dissolution studies rank phosphoric acid as moderately erosive (less than citric acid at equivalent pH), and clinical evidence supports the dental advisory consensus to limit frequency of acidic drink consumption.

Bone mineral density: Multiple cross-sectional and prospective cohort studies have examined cola consumption and BMD or fracture risk. Results are mixed; some report modest inverse associations (particularly for cola in women), while others find no independent effect after covariate adjustment. Controlled phosphate supplementation trials in healthy adults generally do not show adverse bone effects at intakes within the UL.

Renal outcomes: In healthy individuals, phosphate loading studies confirm efficient renal excretion and no sustained elevation in serum phosphate at dietary intakes within the UL. Observational data in CKD populations consistently support dietary phosphate restriction, including from additive sources, as part of disease management.

Cardiovascular markers: Some intervention studies have examined the effect of dietary phosphate loading on fibroblast growth factor 23 (FGF-23), a phosphaturic hormone increasingly recognized as a cardiovascular risk biomarker. Acute inorganic phosphate loading from food additives raises FGF-23 and serum phosphate more rapidly than equivalent organic phosphate loads; the clinical significance of transient elevations in healthy individuals is not established.

In the European Union, phosphoric acid must be declared on food labels by its E number (E338) or by its full name phosphoric acid, as required under EU Regulation (EU) No 1169/2011. Phosphate salts derived from phosphoric acid carry separate E numbers (E339–E341, E343, E450–E452) and may appear under their own names or E numbers.

In the United States, phosphoric acid must be declared in the ingredient list by its common or usual name, i.e. 'phosphoric acid', under FDA labeling regulations (21 CFR Part 101). There is no E-number system in the USA.

In Australia and New Zealand, it may appear as 'phosphoric acid' or 'food acid (338)' under FSANZ labeling standards.

Consumers scanning labels for phosphoric acid should also be aware that phosphate salts (sodium phosphate, calcium phosphate, disodium phosphate, etc.) are chemically related and contribute to total dietary phosphate load but are labeled separately.

Phosphoric acid as such does not occur freely in significant quantities in unprocessed foods; however, inorganic phosphate—the ionised form that phosphoric acid yields in solution—is ubiquitous in the food supply as a naturally occurring constituent of virtually all living cells. Rich natural dietary sources of phosphorus include:

• Dairy products (milk, cheese, yoghurt): 150–800 mg phosphorus per 100 g depending on the product.
• Meat, poultry, and fish: 150–350 mg phosphorus per 100 g, largely as organic phosphate in nucleic acids, phospholipids, and phosphoproteins.
• Legumes and pulses (lentils, chickpeas, soybeans): 100–400 mg phosphorus per 100 g, partly as phytate (less bioavailable).
• Nuts and seeds: 300–600 mg phosphorus per 100 g, also significantly as phytate.
• Whole grains: Variable; much phosphorus bound as phytate reduces net bioavailability.
• Eggs: Approximately 200 mg phosphorus per 100 g.

The key distinction is that naturally occurring organic phosphate is typically 40–60% bioavailable, whereas inorganic phosphate from food additives including phosphoric acid is considered up to 100% bioavailable. This difference in bioavailability has clinical relevance primarily for individuals with phosphate-handling disorders such as advanced CKD.