E-numbers / Other additives / E528
also: Milk of magnesia (pharma)
A mineral compound used to regulate acidity and firm texture in food. The same substance used in milk of magnesia.
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Magnesium hydroxide is an inorganic mineral compound, a white powder formed when magnesium oxide is combined with water.
6
of the 43,325 UK supermarket foods we checked declare E528 in their ingredients
That is under 0.1%, counted by its code or its name.
Counted by NutraSafe from UK supermarket ingredient lists, September 2026. How we counted
Magnesium hydroxide is an inorganic mineral compound, a white powder formed when magnesium oxide is combined with water. It occurs naturally as the mineral brucite and is chemically identical to the active ingredient in the antacid and laxative product known as milk of magnesia. In food use it functions as an acidity regulator and firming agent.
As an acidity regulator it raises or stabilises pH in food systems by neutralising acids. As a firming agent it interacts with pectin and other structural polysaccharides in plant tissue to maintain texture and prevent softening during processing. It is also used as a carrier or bulking agent for other food additives and nutrients. Because it is only sparingly soluble in water it releases alkalinity slowly, making it useful for controlled pH adjustment.
Most commonly found in cocoa and chocolate products where it adjusts acidity during processing, processed cereal products, and some canned or bottled vegetables where it helps maintain firmness. It also appears as a carrier in nutrient preparations and food additive blends. On a label it appears as 'magnesium hydroxide' or 'E528'.
Magnesium hydroxide contributes ionic magnesium when consumed. Magnesium is an essential mineral involved in hundreds of enzyme reactions, muscle function, nerve signalling, and bone mineralisation. The amounts delivered by E528 used as a food additive are small relative to dietary magnesium from whole foods such as nuts, seeds, and leafy vegetables. EFSA and SACN have both characterised magnesium intake and set dietary reference values for the general population.
EFSA has set an adequate intake for magnesium of 350mg per day for adult men and 300mg per day for adult women, based on balance studies and observational data.
SACN concluded that the average UK adult dietary magnesium intake is below the reference nutrient intake for men but broadly adequate for most groups, with no evidence of widespread deficiency requiring supplemental intervention at population level.
At doses used medicinally as a laxative, magnesium hydroxide draws water into the intestine by osmosis and stimulates bowel movement. This effect is well established and dose-dependent. The quantities present in food as E528 are far below laxative doses, but very large intakes of magnesium from all sources combined can cause loose stools. This is a physiological response to excess magnesium, not a toxicological effect.
Magnesium hydroxide acts as an osmotic laxative at doses of 2 to 4 grams per day (equivalent to approximately 1.2 to 2.4 grams of elemental magnesium); doses used in food additive applications are a small fraction of this threshold.
EFSA noted that an acute supplemental magnesium intake of 250mg elemental magnesium per day from all non-food sources did not produce adverse effects in adults, and set this as a tolerable upper level for supplemental magnesium.
EFSA's food additives panel reviewed magnesium salts including magnesium hydroxide and found no indication of genotoxicity, carcinogenicity, or reproductive toxicity from the available data. No numerical ADI was considered necessary because the additive is a normal constituent of diet and the body regulates magnesium absorption and excretion through established homeostatic mechanisms.
EFSA concluded that magnesium hydroxide and other magnesium salts used as food additives did not raise a safety concern at the levels of use reported, and no numerical ADI was required given the essential nutrient status of magnesium.
People with kidney disease or impaired kidney function should be aware that the kidneys are the primary route of magnesium excretion; high total magnesium intake from all sources including supplements and antacids may accumulate. Look for 'magnesium hydroxide' or 'E528' on the label. Anyone taking prescribed medication for heart rhythm, muscle conditions, or kidney disease should check total magnesium intake with their doctor.
Magnesium hydroxide is one of the most thoroughly characterised minerals used in food. It is the same compound found in milk of magnesia, used in medicine for over a century. The science on its behaviour in the body is well established: magnesium is essential, absorbed in the small intestine, and excess is excreted by the kidneys. At additive-use levels the amounts are small. The only documented dose-dependent effect, loose stools, occurs at intake levels orders of magnitude above what food additive use delivers. No genotoxicity, carcinogenicity, or developmental concerns have been identified in regulatory reviews.
No. Magnesium hydroxide is an approved food additive in the UK under the FSA approved-additives list and the assimilated EU Regulation 1333/2008. Its authorisation in Great Britain has been in effect since 31 December 2020.
Yes. The active ingredient in milk of magnesia (the antacid and laxative medicine) is magnesium hydroxide. In food use the same compound is added at much smaller amounts to adjust acidity or firm texture, not to produce a laxative effect.
Magnesium hydroxide is used mainly in cocoa and chocolate products, processed cereals, and some canned or bottled vegetables. It also appears as a carrier in food additive and nutrient blends. Check the ingredients list for 'magnesium hydroxide' or 'E528'.
Yes. Magnesium hydroxide is a mineral compound with no animal-derived ingredients. It is suitable for vegans and vegetarians.
Last reviewed: 20 June 2026
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