Magnesium oxide vs magnesium citrate

At a glance: magnesium oxide vs citrate

Magnesium oxide contains 60.3 % elemental magnesium and trimagnesium dicitrate 16.2 %, both on an anhydrous basis. The oxide is therefore about 3.7 times as concentrated. 166 mg of oxide delivers 100 mg of magnesium, against 619 mg of the citrate. The oxide is practically insoluble in water and suits compact tablets and capsules. The citrate dissolves more readily and tastes tart, which suits powders, drinks and effervescent formats.

For magnesium citrate against a chelated form, see magnesium citrate vs magnesium glycinate. Every form is covered in the magnesium forms guide.

Content per gram and label-claim arithmetic

Powder needed equals the label claim divided by the elemental fraction. Start from the anhydrous figures, then correct for the water content of the grade you buy.

At 200 mg of magnesium, the oxide fits a single small tablet or capsule and leaves room for other actives. The citrate needs about 1.24 g of powder. That usually means several capsules or a large tablet per serving. In a stick pack or drink powder, the same mass is a modest share of the fill.

Hydrated grades carry less magnesium per gram than the anhydrous figure. Trimagnesium dicitrate is traded in anhydrous and hydrated forms, so read the water content and assay before calculating. SoleChem sends the specification sheet and the certificate of analysis with its quote. Add manufacturing overage on top: the elemental content calculator and the overage calculator handle both steps.

Solubility, taste and processing

Magnesium oxide is practically insoluble in water and dissolves in acids. It is alkaline. In a powder or effervescent blend it reacts with acidulants such as citric acid, shifting pH and reducing fizz. On exposure to air it slowly takes up moisture and carbon dioxide, so keep containers closed between uses.

The oxide is sold in light and heavy grades that differ in bulk density. The denser grade puts more mass into a given capsule volume and is easier to handle on a tablet press. Fine, light grades flow poorly and are usually granulated or blended before compression. In a drink, undissolved particles feel chalky and gritty.

Trimagnesium dicitrate dissolves far better than the oxide. Its exact solubility depends on grade and hydration, and the specification sheet states it. The sour taste fits fruit-flavoured powders and effervescent tablets but needs masking in neutral products. Its larger mass per serving makes high-claim citrate tablets bulky, so binder choice and coating matter.

The same trade-off between an insoluble, concentrated salt and a citrate appears with calcium: see calcium carbonate vs calcium citrate.

EU regulatory status

Annex II of Directive 2002/46/EC lists both as magnesium sources for food supplements. Magnesium oxide is listed by name. Trimagnesium dicitrate falls under the entry for magnesium salts of citric acid. The permitted forms guide covers the full list.

Both substances also have E numbers under Regulation (EC) No 1333/2008: E530 for magnesium oxide and E345(i) for the citrate. Specifications for food additives are set in Regulation (EU) No 231/2012. Used as a magnesium source, the material falls under the Directive, which also requires listed forms to meet applicable EU purity criteria.

Maximum amounts of magnesium in food supplements are set nationally and differ between member states. See maximum levels by EU country. The label declares the amount of magnesium, not the amount of salt. The labelling guide covers the format, and authorised claim wording is in the EU Register of nutrition and health claims.

Choosing between them

• High claim in a small unit: the oxide, because it needs about a quarter of the citrate’s mass.
• Multi-ingredient tablets and capsules: the oxide leaves fill volume or tablet mass for other actives.
• Drink powders and sachets: the citrate dissolves better and its taste suits flavoured systems; see powders and sports nutrition.
• Effervescent tablets: the citrate, since the oxide consumes acid from the effervescent couple.
• Cost per milligram of magnesium: usually lower for the oxide, because less material carries each milligram.
• Product concept: the ingredients list names the form used, so the concept may dictate the salt.

Combining both makes sense when a product needs a compact unit and a citrate source. A tablet can take most of its magnesium from the oxide and the rest from citrate. Calculate each form separately, add the elemental amounts for the declared total and list both forms. If you are trialling a blend, ask for both materials in the quote form.