Magnesium citrate

Grades and forms

Magnesium citrate powder contains 16.2 % elemental magnesium on an anhydrous basis. To declare 100 mg of magnesium per serving, you need about 619 mg of anhydrous magnesium citrate. Manufacturers buy it in bulk for capsules, tablets, drink powders and effervescent formats.

Three points decide the grade:

• Hydration state. Magnesium citrate is traded both anhydrous and as hydrates. Water of crystallisation lowers the magnesium content per gram as supplied. The 16.2 % figure applies only to anhydrous material.
• Identity. This page covers trimagnesium dicitrate (CAS 3344-18-1), the anhydrous salt Mg3(C6H5O7)2 with a molar mass of 451.11 g/mol. Other CAS numbers are also traded as magnesium citrate with a different magnesium content, so check the CAS number and magnesium content on the specification sheet.
• Physical form. Fine powder suits blends and capsule filling. Granular material flows more freely and is the usual choice for direct compression.

The certificate of analysis states the assay, the water content and the basis for each batch. SoleChem sends the specification sheet and the certificate of analysis with its quote. Ask for the grade you need in the quote form.

EU regulatory status

Magnesium is listed in Annex I of Directive 2002/46/EC. Annex II of the same Directive lists “magnesium salts of citric acid” among the mineral substances permitted in food supplements. The same entry appears in Annex II of Regulation (EC) No 1925/2006, which covers the addition of minerals to other foods. The guide to permitted vitamin and mineral forms explains how the lists work.

The EU has not adopted harmonised maximum amounts of magnesium in food supplements. Member states set their own limits, and these differ. The maximum levels guide explains how national rules apply.

Under Article 8 of Directive 2002/46/EC, the label states the amount of magnesium in numerical form per portion recommended for daily consumption. The amount declared is the magnesium, not the citrate salt. See labelling a food supplement in the EU.

Any health claim must be authorised under Regulation (EC) No 1924/2006. The authorised wording is in the EU Register of nutrition and health claims. The health-claims guide covers the conditions of use.

Formulation notes

Divide the label claim by the elemental fraction to find the powder mass:

• 100 mg magnesium: about 619 mg anhydrous magnesium citrate
• 200 mg magnesium: about 1,237 mg anhydrous magnesium citrate

For hydrated material, use the magnesium content on the as-supplied basis from the certificate of analysis. Add any overage on top of this figure. The elemental content calculator and the overage calculator do both steps.

Capsules. The powder mass per serving is large. Higher claims are often split across several capsules or combined with a denser form. Fine powder may need a glidant such as silicon dioxide. See ingredients for capsules.

Tablets. Tablet mass rises quickly with the claim. Granular grades or a granulation step help with flow and compression. See ingredients for tablets.

Powders and effervescent tablets. Magnesium citrate disperses and dissolves in water more readily than magnesium oxide. This makes it a common choice for drink powders. Its taste is tart and slightly bitter, so flavour masking is usually needed. It fits citric acid and bicarbonate systems; see ingredients for effervescent tablets.

Moisture. Anhydrous material takes up moisture from the air. Keep containers sealed and check compatibility with moisture-sensitive actives in the same blend.

How magnesium citrate compares to other forms

For side-by-side detail, see magnesium citrate vs magnesium glycinate and magnesium oxide vs magnesium citrate. All forms are covered in the magnesium forms guide.