Magnesium — Complete Supplement Guide (forms, doses, absorption)

SupplementsMineralsMagnesium

One of the minerals a large share of adults fall short of — which, together with its role in sleep, muscle and mood, is why it’s so widely supplemented. For the short dietary version, see the Minerals page.

Read first. The therapeutic doses below describe research and clinical use — information, not a prescription. Magnesium supplements interact with several medicines and can accumulate dangerously in kidney disease. Always check with a doctor or pharmacist before therapeutic use, in pregnancy, in kidney impairment, or alongside other medication.

Key takeaways

Widely useful (sleep, muscle, mood) and many adults fall short.
Adults need ≈ 300–420 mg/day; typical supplement 200–400 mg elemental.
Supplemental upper limit 250 mg (EFSA) / 350 mg (US) — above that, loose stools.

Function

Magnesium is a cofactor in more than 300 enzyme systems (by some counts 600+), so it touches almost every major process in the body:

Energy metabolism: ATP — the cell's energy currency — is biologically active only as a magnesium complex (Mg-ATP), and the enzymes of glycolysis and the mitochondria that release energy from food all depend on magnesium.
Muscle contraction & relaxation: works as the natural counterpart to calcium — calcium drives contraction, magnesium promotes relaxation — so it is central to normal muscle tone and to preventing cramps.
Nerve signalling: regulates the excitability of nerve cells, partly by gating the NMDA receptor; this calming action underlies its links to sleep, stress and headache.
Heart rhythm: stabilises the electrical conduction of the heart; low magnesium predisposes to arrhythmia.
Bone structure: about 60% of body magnesium is in bone, where it supports the mineral lattice and overall bone quality.
Electrolyte balance: required by the sodium–potassium pump and to keep potassium and calcium properly distributed — low magnesium causes stubborn low potassium and low calcium that won't correct until magnesium is replaced.
Vitamin D & calcium handling: the enzymes that activate vitamin D and the secretion of parathyroid hormone both need magnesium.
Blood sugar: needed both to secrete insulin and for insulin to work; low magnesium is linked to insulin resistance.
Blood pressure & vascular tone: helps relax blood-vessel walls.
DNA, RNA & protein synthesis: a structural cofactor for building and repairing genetic material and proteins.

Different forms — and which to choose

A magnesium supplement is always a salt: magnesium bound to a carrier — an oxide, an organic acid or an amino acid. The carrier decides two things. First the elemental magnesium content: how much actual magnesium each gram of the salt contains. Second the bioavailability: how much of that magnesium your body can absorb. The two often pull in opposite directions — oxide packs the most magnesium per gram but dissolves poorly, while organic salts like citrate and glycinate carry less per gram yet deliver more of it into the blood. And there is a practical side effect hiding in the same chemistry: magnesium that is not absorbed stays in the gut and draws in water, so the poorly absorbed forms are also the most laxative ones.

Oxide~60% elemental — the most concentrated, and the worst absorbed. An inorganic salt that dissolves poorly in the digestive tract. In a human study of commercial products, only about 4% of the magnesium in oxide was absorbed, while chloride, lactate and aspartate salts did significantly better,⁵ and in a 60-day randomised trial oxide performed no better than placebo on absorption measures.⁶ The unabsorbed remainder is what makes oxide so strongly laxative. Cheap, and fine if the laxative effect is precisely what you want — a poor tool for correcting low magnesium. Read more about oxide →

Citrate~16% elemental; the best-documented absorption of the common forms. Bound to citric acid, it dissolves readily even when stomach acid is low. It beat oxide clearly in a classic solubility-and-absorption comparison,⁷ and in the 60-day randomised trial above it produced the highest serum and saliva magnesium of all the forms tested — including an amino-acid chelate.⁶ Mildly laxative at higher doses, which many people never notice at 200–300 mg. Good value and easy to find: a sensible everyday all-rounder. Read more about citrate →

Glycinate
(bisglycinate)~14% elemental; well absorbed and the gentlest on the gut. Magnesium chelated to two molecules of the amino acid glycine. The chelate stays soluble through the whole gut, and part of it appears to be taken up via peptide absorption routes rather than the ordinary mineral channels — in patients with surgically shortened intestines, diglycinate was absorbed better than oxide.⁸ Because little is left unabsorbed in the gut, it is the form least likely to loosen stools. Glycine itself has a mild calming quality, which is why glycinate is the usual pick for evening use, sleep, stress and long-term supplementation. Read more about glycinate →

Malate~15% elemental; well absorbed and well tolerated. Bound to malic acid, the tart acid in apples. In an animal comparison of five forms, malate gave the highest overall blood magnesium and stayed elevated in serum the longest⁹ — though human head-to-head data are thinner than for citrate. Non-laxative for most people and slightly "neutral" in feel compared with glycinate, so it is often chosen for daytime use and for fatigue or muscle complaints — plausible uses, but not specifically proven ones. Read more about malate →

L-threonateOnly ~8% elemental — chosen for the brain, not for efficiency. This form was developed after a rodent study showed it raised magnesium levels in the brain and improved learning and memory,¹⁰ and one small manufacturer-sponsored human trial reported better cognition in older adults with mild impairment.¹¹ Promising but early evidence — and you pay several times the price of citrate for a fraction of the elemental magnesium. Not the form to pick for correcting an ordinary low intake. Read more about L-threonate →

Taurate~9% elemental. Magnesium bound to taurine, an amino acid involved in heart-muscle function and blood-pressure regulation — the theoretical reason this form is marketed for cardiovascular support. Absorption looks good: in the animal comparison above, the related acetyl-taurate form was rapidly absorbed and reached the highest brain concentrations of the forms tested.⁹ Direct human trials of magnesium taurate itself are still lacking, so any heart benefit rests on magnesium (and taurine) generally rather than on this particular salt. Read more about taurate →

Sulfate / chlorideThe medical and bath-salt forms. Sulfate is Epsom salt: by IV it is the hospital treatment for eclampsia and severe deficiency, and taken by mouth it is strongly laxative. As a bath it is pleasant — but the evidence that magnesium is absorbed through the skin is weak to non-existent, so a soak should be enjoyed as a soak, not counted as supplementation.¹² Chloride (~12% elemental) dissolves very well and was among the better-absorbed salts in the human comparison above;⁵ it appears in liquid supplements and "magnesium oils", where the same skin caveat applies.

Practical take: for general use choose citrate (best-documented, good value) or glycinate (gentlest, suits evening use); use oxide only if you actually want the laxative effect. The differences between the well-absorbed forms are smaller than the marketing suggests — taking magnesium with food and splitting the dose over the day does at least as much for absorption as the choice of salt. And always read the elemental magnesium figure on the label, not the total salt weight.

Absorption in the body

How muchRoughly 30–40% of dietary magnesium is absorbed, mostly in the small intestine. Fractional absorption rises when intake is low and falls when it is high — the body self-regulates, with the kidneys fine-tuning what is kept or excreted.

HelpsAdequate vitamin D; spreading intake across the day; taking supplements with food; organic forms (citrate/glycinate).

HindersVery high doses at once (spills into the gut → diarrhoea), high-dose calcium or zinc taken at the same time, excess alcohol, high phytate (raw bran) and certain medicines (PPIs, some diuretics) which increase losses.

Deficiency symptoms

Overt deficiency is under-diagnosed because blood levels stay near-normal until stores are quite low (most magnesium is inside cells and bone, not in blood).

Early signsMuscle cramps and twitches, fatigue, poor sleep, low mood or irritability, headaches.

AdvancedAbnormal heart rhythm, numbness/tingling, and hard-to-correct low potassium and low calcium (magnesium is needed to keep both in balance).

Who's at riskLow intake/processed diets, heavy alcohol use, GI disease (Crohn's, coeliac), type 2 diabetes, older adults, and long-term use of PPIs or diuretics.

Recommended intake

Adults ≈ 300–420 mg/day

General adult reference intakes (varies by body size, sex and life stage):

Women: ~300–320 mg/day
Men: ~350–420 mg/day
Pregnancy: ~+40 mg/day above baseline

Best food sources: pumpkin and other seeds, nuts (almonds, cashews), dark leafy greens, legumes, whole grains and dark chocolate. Much magnesium is lost when grains are refined.¹ ²

Therapeutic use

Strong evidenceConstipation (osmotic laxative — oxide/citrate); eclampsia & pre-eclampsia (IV magnesium sulfate, a hospital treatment); correcting proven deficiency and related low potassium/calcium.

ReasonableMigraine prevention (recognised as an option by headache guidelines); modest lowering of blood pressure; better insulin sensitivity where intake was low.³

Modest / mixedSleep and anxiety/stress (small benefits, better data in people who are low); leg cramps — largely unproven despite popularity.

Therapeutic doses

Common supplemental: 200–400 mg elemental/day

General top-up200–400 mg elemental/day, ideally with food and split into two doses to improve absorption and reduce loosening of the stool.

Migraine preventionStudied at ~400–600 mg/day (often citrate), taken for several weeks to judge effect.

ConstipationMagnesium oxide/citrate as directed on the product — the laxative effect is the goal here.

RememberDoses refer to elemental magnesium. Because forms differ in elemental content, always check the label, and count supplement magnesium toward the upper limit below.

Toxicity & upper limit

Supplemental UL: 250 mg/day (EFSA) · 350 mg (US)

Upper limitThe tolerable upper level applies to magnesium from supplements, not from food: 250 mg/day (EFSA) or 350 mg/day (US NIH). Food magnesium has no upper limit — healthy kidneys excrete the excess.¹ ⁴

First sign of excessDiarrhoea and stomach cramps — the practical limiter for most people.

Real toxicityDangerous hypermagnesemia (low blood pressure, confusion, muscle weakness, slow/irregular heartbeat) is rare and occurs almost only with kidney impairment or very high medicinal doses. Avoid magnesium supplements in significant kidney disease unless supervised.

InteractionsCan reduce absorption of some antibiotics (tetracyclines, quinolones) and bisphosphonates and thyroid medicine (levothyroxine) — separate doses by 2–4 hours. Adds to the effect of some blood-pressure medicines.

Bottom line: aim for magnesium from seeds, nuts, greens, legumes and whole grains first. If supplementing, citrate or glycinate at 200–400 mg elemental/day suits most people; keep supplemental intake near the upper limit unless a professional advises more, and be cautious with kidney disease and interacting medicines.

← All supplements Short dietary version

References

Reference and upper-limit values are general adult figures from official bodies; individual needs vary. Therapeutic doses describe clinical/research use, not prescriptions.

US NIH Office of Dietary Supplements. Magnesium — Health Professional Fact Sheet (function, intakes, food sources, deficiency, therapeutic uses, UL, interactions). ods.od.nih.gov
EFSA Panel (NDA). Dietary Reference Values for magnesium. EFSA Journal 2015;13(7):4186. efsa.onlinelibrary.wiley.com
Zhang X, et al. Effects of magnesium supplementation on blood pressure: a meta-analysis of randomized double-blind placebo-controlled trials. Hypertension 2016;68(2):324–333. ahajournals.org
EFSA Scientific Committee on Food. Tolerable Upper Intake Level of magnesium (250 mg/day from supplements). efsa.europa.eu (UL summary)
Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnes Res. 2001;14(4):257–262. PMID 11794633
Walker AF, Marakis G, Christie S, Byng M. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnes Res. 2003;16(3):183–191. PMID 14596323
Lindberg JS, et al. Magnesium bioavailability from magnesium citrate and magnesium oxide. J Am Coll Nutr. 1990;9(1):48–55. PMID 2407766
Schuette SA, Lashner BA, Janghorbani M. Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection. JPEN J Parenter Enteral Nutr. 1994;18(5):430–435. PMID 7815675
Uysal N, et al. Timeline (bioavailability) of magnesium compounds in hours: which magnesium compound works best? Biol Trace Elem Res. 2019;187(1):128–136 (animal study). PMID 29679349
Slutsky I, et al. Enhancement of learning and memory by elevating brain magnesium. Neuron. 2010;65(2):165–177 (animal study). PMID 20152124
Liu G, et al. Efficacy and safety of MMFS-01, a synapse density enhancer, for treating cognitive impairment in older adults: a randomized, double-blind, placebo-controlled trial. J Alzheimers Dis. 2016;49(4):971–990. PMID 26519439
Gröber U, Werner T, Vormann J, Kisters K. Myth or reality — transdermal magnesium? Nutrients. 2017;9(8):813. PMID 28788060

This article summarizes nutrition science from official health authorities and peer-reviewed sources for education. It is not a substitute for individual medical advice, and the doses given are not prescriptions — always consult a professional before therapeutic supplement use, in pregnancy, in kidney disease, or alongside medication.

Magnesium — The Complete Supplement Guide