How to Choose a Magnesium Supplement: Reading the Label

Three numbers decide a magnesium label: the elemental magnesium per daily dose, how many capsules or scoops that dose takes, and whether it reaches 56.25 mg, which is 15% of the 375 mg reference value and the point at which a label may carry the authorised magnesium wordings.^{1, 2} Form, fillers and format come after, and no trial ranks one above another.³ It is the label-reading guide within the Wellgard vitamins and minerals guide.

What is elemental magnesium, and why is the compound weight a different number?

Elemental magnesium is the mineral itself; in a supplement it is bound to a carrier (an oxide, a citrate, two glycine molecules) that weighs far more than the magnesium in it. The nutrition panel must state magnesium in milligrams and as a percentage of the 375 mg reference value, so the panel line is the figure to use, not the compound weight in the ingredients list.¹ The percentages below are calculated from each compound's formula and move with the hydrate a maker uses, so "glycinate is 14%" is true of one named compound, not of every product.⁴

L-threonate is 7 to 8% magnesium, so 2,000 mg carries about 145 to 165 mg, and a "500 mg" tablet can mean 300 mg of magnesium or 55 mg.⁴ Read the panel's magnesium line, multiply by the servings a day the directions give, and if a label states only compound weight, ask the maker for the elemental figure (the same point as on types of creatine compared).

What does the 15% NRV line on a label mean?

375 mg is the nutrient reference value for magnesium in retained Regulation 1169/2011, and 15% of it per portion, 56.25 mg, is the "significant amount" a single-portion product must supply to be called a source of magnesium.¹ That threshold is the condition on every magnesium wording in the Great Britain register, which lists ten: "Magnesium contributes to a reduction of tiredness and fatigue"; "Magnesium contributes to electrolyte balance"; "Magnesium contributes to normal energy-yielding metabolism"; "Magnesium contributes to normal functioning of the nervous system"; "Magnesium contributes to normal muscle function"; "Magnesium contributes to normal protein synthesis"; "Magnesium contributes to normal psychological function"; "Magnesium contributes to the maintenance of normal bones"; "Magnesium contributes to the maintenance of normal teeth"; "Magnesium has a role in the process of cell division".² A label uses the wording as written, keeping "contributes to" and naming magnesium. The register holds no magnesium wording about sleep, anxiety, stress, calm, cramps, blood pressure or cognition.²

How do you read a blend or "complex" label?

No trial has compared a blend of magnesium salts with a single salt, so a blend is read by the panel's one magnesium figure.³ The ingredients list names each compound in descending order of weight, which shows which salt supplies most, not how much magnesium each contributes; "buffered" glycinate means magnesium oxide has been added, and both are listed. The 2017 review's point: magnesium "cannot be stored but only retained for current needs, a higher absorption is usually followed by a higher excretion of the mineral".³

Which form should you choose?

The 2017 review concluded that "it remains unclear which Mg2+ binding form produces the highest bioavailability" and that the dose "combined with the endogenous Mg2+ status is more important".³ In 46 people taking 300 mg a day for 60 days, citrate and an amino-acid chelate raised urinary magnesium more than oxide, citrate raised serum magnesium most, and red-cell magnesium did not differ between any group.⁵ Running the other way, a 41-person crossover found a month of 520 mg a day as oxide raised the magnesium inside cells more than 296 mg a day as citrate, at unequal doses.⁶ Bisglycinate's human data are few: a 12-person isotope study in bowel-resection patients found it absorbed no differently from oxide, better in the four poorest absorbers, and "better tolerated by all patients".⁷ Malate has no human bioavailability trial of its own. Choose by elemental dose, servings and the salt you tolerate; the study-by-study table is on which magnesium is best, with depth on what magnesium glycinate is and what magnesium citrate is.

Tablets, capsules, powders, gummies or drinks: what does each deliver?

No trial has compared magnesium formats for absorption, so the label is the only comparison.⁸ The one dose-response study found the share absorbed falls as a single dose rises, from 65% to 11%, so serving size matters.⁸ Tablets and capsules state a dose per unit and units a day. Powders state a dose per scoop. Gummies state a figure per gummy, often with sugar listed. Drinks carry a figure per bottle, and for beverages the significant amount is 7.5% of the reference value per 100 ml.¹ Sprays, oils, flakes and bath salts are not food supplements; their studies are on sprays and baths. Splitting a dose across servings is on when to take magnesium, and the daily figures by age and sex on how much magnesium per day.

What do the UK rules let a supplement contain and say?

UK law lists the magnesium compounds a food supplement may use, in the retained annex to the food supplements directive.⁹ Magnesium L-threonate came by a separate route: Europe's food-safety panel found it safe in 2024 for adults at up to 3,000 mg a day, about 250 mg of magnesium, "except for pregnant and lactating women", and England set purity criteria for it in 2026.^{4, 10} That is a safety decision, not a claim. The list is on every permitted form and its elemental content. On dose, the NHS says 400 mg or less a day from supplements is "unlikely to cause any harm" (page last reviewed 3 August 2020); 400 mg is the 2003 Expert Group guidance level, "For guidance purposes only"; and Europe's upper level for supplemental magnesium is 250 mg a day, the highest dose with no loose stools in trials.^{11, 12, 13} Kidney disease is the one condition in which magnesium accumulates, so anyone with it asks their kidney team first; the everyday limits are on is it OK to take magnesium every day and the medicines to separate from it on what you should not take with magnesium.

What are the fillers and extras, and does magnesium stearate matter?

Below the active compound sit the capsule shell, a bulking agent and a flow agent, usually magnesium stearate: the magnesium salt of stearic acid, additive E 470b, which Europe's additives panel re-evaluated in 2018 and found "of no safety concern at the reported uses and use levels".¹⁴ At about 4% magnesium and milligram amounts, it is not a magnesium source.⁴ "Chelated" means magnesium bound to an amino acid such as glycine; no trial shows chelation adds anything beyond the magnesium delivered.^{5, 7} Partner nutrients such as vitamin B6, zinc and vitamin D are read by their own register wordings, each with its own 15% condition, and do not change the magnesium figure.²

What does the NHS say about which magnesium supplement to buy?

It names none. The NHS page, last reviewed 3 August 2020, says you should be able to "get all the magnesium you need by eating a varied and balanced diet".¹¹ A supplement is the usual way to close a gap when intake is low or a medicine lowers your level, and magnesium contributes to normal muscle function and to a reduction of tiredness and fatigue.^{2, 11} The same method is applied on how to choose a multivitamin for women and how to choose a melatonin-free sleep supplement.

What we don't know

No trial has compared the common salts in healthy adults at the same elemental dose for absorption or loose stools, and none has compared formats.^{3, 8} The hydrate behind any one label is the maker's, so the table above is arithmetic, not a measurement; and the permitted list moves, so the regulatory pages here are rechecked at each review.

Frequently asked questions

Which magnesium should I take?

The one whose panel gives the elemental dose you want, within the 400 mg guidance level, in servings you will take, in a salt you tolerate; the absorption studies do not rank the common salts for anyone in particular.^{3, 11, 12}

Is 500 mg of magnesium too much?

500 mg a day of magnesium is above the UK 400 mg guidance level and the European 250 mg upper level, and the NHS says more than 400 mg for a short time can cause diarrhoea.^{11, 12, 13} Check whether the 500 mg is compound or elemental: 500 mg of oxide is about 300 mg of magnesium, of bisglycinate about 70 mg.⁴ What trials at 500 mg and above recorded is on magnesium side effects.

What should a magnesium glycinate label say?

The compound name (glycinate and bisglycinate are the same), the elemental magnesium per serving in milligrams and as a percentage of 375 mg, the servings a day, and whether it is "buffered" with oxide.¹ Bisglycinate is about 14% magnesium, so 1,000 mg of compound is about 140 mg.⁴

Is magnesium stearate safe?

Europe's additives panel found E 470b "of no safety concern at the reported uses and use levels" in 2018; a capsule holds a few milligrams as flow agent, adding nothing to the dose.¹⁴

Sources

Regulatory pages last checked 12 October 2026.

1. Retained Regulation (EU) 1169/2011, Annex XIII (nutrient reference values). legislation.gov.uk.
2. Retained Regulation (EU) 432/2012, Annex (permitted health claims). legislation.gov.uk.
3. Schuchardt JP, Hahn A. Intestinal absorption and factors influencing bioavailability of magnesium: an update. 2017. PubMed 29123461.
4. EFSA NDA Panel. Safety of magnesium L-threonate as a novel food and bioavailability of magnesium from this source. 2024. doi.org/10.2903/j.efsa.2024.8656.
5. Walker AF, et al. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. 2003. PubMed 14596323.
6. Shechter M, et al. Comparison of magnesium status using X-ray dispersion analysis following magnesium oxide and magnesium citrate treatment of healthy subjects. 2012. PubMed 22433473.
7. Schuette SA, et al. Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection. 1994. PubMed 7815675.
8. Fine KD, et al. Intestinal absorption of magnesium from food and supplements. 1991. PubMed 1864954.
9. Retained Directive 2002/46/EC on food supplements, Annex II. legislation.gov.uk.
10. The Food Supplements Purity Criteria (Magnesium L-threonate monohydrate) (England) Regulations 2026, SI 2026/680. legislation.gov.uk.
11. NHS. Vitamins and minerals: others, magnesium section. Page last reviewed 3 August 2020; next review was due 3 August 2023. nhs.uk.
12. Expert Group on Vitamins and Minerals. Safe Upper Levels for Vitamins and Minerals: magnesium, 2003. UK Government Web Archive.
13. Scientific Committee on Food. Opinion on the Tolerable Upper Intake Level of Magnesium, 2001 (EFSA compilation, 2006). efsa.europa.eu.
14. EFSA ANS Panel. Re-evaluation of sodium, potassium and calcium salts of fatty acids (E 470a) and magnesium salts of fatty acids (E 470b) as food additives. 2018. PubMed 32625824.