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.

Sources checked on 4 November 2026.

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.

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"; and in an unpublished 2007 crossover of 14 volunteers, summarised in a 2018 European assessment of a manufacturer's dossier, a buffered bisglycinate gave the highest 24-hour serum curve of four forms and oxide the lowest.^{7, 15} Malate's human record is two studies, neither a published head-to-head trial: that same crossover, in which serum magnesium over 24 hours was lower after oxide than after di-magnesium malate, bisglycinate or oxide-buffered bisglycinate (0.109 against 0.196, 0.164 and 0.225, units not stated), and a 91-adult placebo-controlled study of a timed-release malate tablet with B vitamins, with one author at a nutrition company, which measured blood and red-cell magnesium over 30 to 90 days with no other salt to compare.^{15, 16} Choose by elemental dose, servings and the salt you tolerate; the study-by-study table is on which magnesium is best, with more on magnesium glycinate and magnesium citrate.

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, capsules and powders state a dose per unit or scoop. Gummies state a figure per gummy, often with sugar or a polyol sweetener listed; no magnesium gummy has been tested for absorption or tolerance (PubMed, searched 4 November 2026), and the two gummy-against-tablet trials that exist are for other nutrients, a vitamin D gummy absorbed better than a tablet in 31 adults and a vitamin C gummy bioequivalent to a caplet in 30, both single doses of a maker's own product, so neither transfers to magnesium.^{17, 18} Count gummies against the elemental amount you want: the one four-week bisglycinate sleep trial used 250 mg of magnesium a day, so a gummy supplying 50 mg of magnesium would need five a day and one supplying 125 mg two.¹⁹ Polyol sweeteners add their own bowel effect to the magnesium's; sugar and sweeteners in gummy vitamins has the thresholds. 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. Dose timing is on when to take magnesium, the daily figures 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 Schedule 2 to the Nutrition (Amendment etc.) (EU Exit) Regulations 2019: 23 entries, the food supplements directive's 21 plus magnesium citrate malate (2023) and magnesium L-threonate monohydrate (2026).⁹ Magnesium L-threonate also needed a novel-food authorisation: 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; see is it OK to take magnesium every day and 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 carry their own register wordings and 15% conditions and do not change the magnesium figure.²

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

It names none. The NHS 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}

What we don't know

The trials that set the common salts side by side at the same elemental dose measured urine and blood, and no trial has compared them for loose stools beyond one company-funded single dose; none has compared formats.^{3, 5, 8} The hydrate behind any one label is the maker's, so the table above is arithmetic, not a measurement.

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.^{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 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 10 to 14% magnesium by weight, so 1,000 mg of compound is about 100 to 140 mg.⁴ A figure that works out at 20% magnesium from "glycinate" (200 mg from 1,000 mg) is above the 14.1% a dry bisglycinate carries, so look for oxide or another salt in the ingredients list.

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

Does magnesium work better with vitamin B6?

The pairing has one head-to-head trial: 264 healthy adults with low blood magnesium and high stress scores took 300 mg of magnesium a day with or without 30 mg of vitamin B6 for eight weeks, in a trial funded and designed by the maker of the combination product, investigator-blinded, with no placebo arm. Stress scores fell by 44.9% with B6 and 42.4% without, no difference overall, with a 24% greater fall in the subgroup who started with severe stress; a secondary analysis found the B6 did not raise red-cell magnesium any further.^{20, 21} Vitamin B6 carries its own authorised wordings, among them "Vitamin B6 contributes to normal psychological function" and "Vitamin B6 contributes to the reduction of tiredness and fatigue", at its own 15% condition, and the NHS says not to take more than 10 mg a day in supplements unless a doctor advises, because 200 mg or more a day can cause a loss of feeling in the arms and legs; the trial's 30 mg sits above that 10 mg line.^{2, 22} So on a label B6 adds its own roles, not a measured boost to the magnesium.

Sources

1. Retained Regulation (EU) 1169/2011, Annex XIII (nutrient reference values and significant amounts). 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. Current Nutrition and Food Science, 2017. Review; no conflict declared. PubMed 29123461.
4. EFSA NDA Panel. Safety of magnesium L-threonate as a novel food and bioavailability of magnesium from this source. EFSA Journal, 2024. PubMed 38481468.
5. Walker AF, et al. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium Research, 2003. Randomised double-blind trial, 46 healthy adults, 300 mg a day for 60 days; research support from a source other than the US government listed on PubMed, funder not named. 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. Magnesium Research, 2012. Randomised crossover, 41 healthy adults, one month on each salt; funding not stated on PubMed. PubMed 22433473.
7. Schuette SA, et al. Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection. Journal of Parenteral and Enteral Nutrition, 1994. Randomised crossover, 12 patients, single 100 mg dose; US public research funding listed on PubMed (NIH and FDA grants). PubMed 7815675.
8. Fine KD, et al. Intestinal absorption of magnesium from food and supplements. Journal of Clinical Investigation, 1991. Absorption study in healthy adults, 0 to 80 mEq with a meal; US public research funding listed on PubMed (NIH grants) and research support from a non-US source. PubMed 1864954.
9. The Nutrition (Amendment etc.) (EU Exit) Regulations 2019, SI 2019/651, Schedule 2 Part B: mineral substances which may be used in the manufacture of food supplements. Latest available (revised) text, read 4 November 2026; footnotes F2 (magnesium citrate malate inserted 10 February 2023 by SI 2023/28), F3 and F4 (magnesium L-threonate monohydrate inserted 5 March 2026 for Scotland and Wales and 12 August 2026 for England). legislation.gov.uk. Origin of the list: Directive 2002/46/EC, 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 (review overdue). 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. EFSA Journal, 2018. PubMed 32625824.
15. EFSA ANS Panel. Evaluation of di-magnesium malate, used as a novel food ingredient and as a source of magnesium. EFSA Journal, 2018. Regulatory opinion on a manufacturer's dossier, summarising an unpublished 2007 four-arm crossover in 14 healthy volunteers (section 3.4.1). PubMed 32625931.
16. Weiss D, Brunk DK, Goodman DA. Scottsdale Magnesium Study: absorption, cellular uptake, and clinical effectiveness of a timed-release magnesium supplement in a standard adult clinical population. Journal of the American College of Nutrition, 2018. Placebo-controlled study, 91 adults (53 on the product), 30 to 90 days; one author at a nutrition company; research support from a source other than the US government listed on PubMed, funder not named. PubMed 29425476.
17. Wagner CL, et al. Bioequivalence studies of vitamin D gummies and tablets in healthy adults: results of a cross-over study. Nutrients, 2019. Randomised crossover, 9 then 31 adults, single 20,000 IU doses; a US translational-science grant and a gummy maker listed as funders on PubMed. PubMed 31067745.
18. Evans M, et al. Vitamin C bioequivalence from gummy and caplet sources in healthy adults: a randomized-controlled trial. Journal of the American College of Nutrition, 2020. Randomised crossover, 30 adults, single 1,000 mg doses; authors at the gummy maker and a contract-research company. PubMed 31747355.
19. Schuster J, et al. Magnesium bisglycinate supplementation in healthy adults reporting poor sleep: a randomized, placebo-controlled trial. Nature and Science of Sleep, 2025. 155 adults, 250 mg of magnesium a day as bisglycinate (with 1,523 mg of glycine), 4 weeks; funded by a German university institute; one author directs a contract-research company funded by supplement makers. PubMed 40918053.
20. Pouteau E, et al. Superiority of magnesium and vitamin B6 over magnesium alone on severe stress in healthy adults with low magnesemia: a randomized, single-blind clinical trial. PLoS One, 2018. 264 adults, 8 weeks, no placebo arm; funded by the manufacturer of the combination product, which took part in the design and analysis; several authors employed by or paid by it. PubMed 30562392.
21. Noah L, et al. Impact of magnesium supplementation, in combination with vitamin B6, on stress and magnesium status: secondary data from a randomized controlled trial. Magnesium Research, 2020. Secondary analysis of the trial above; three of its authors employed by the manufacturer. PubMed 33210604.
22. NHS. Vitamins and minerals: B vitamins and folic acid, vitamin B6 section. Page last reviewed 3 August 2020 (review overdue). nhs.uk.

Spotted something out of date? Email support@wellgard.co.uk with the page address and the sentence.