Magnesium
Magnesium is a cofactor in more than 300 enzyme systems, including every reaction that uses ATP, which exists in cells mainly as a magnesium-ATP complex. About half of Americans eat less than the Estimated Average Requirement, and the chemical form of a supplement largely determines how much of the labeled dose is absorbed.
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What It Does
Magnesium stabilizes ATP for kinase reactions, is required by DNA and RNA polymerases, and acts as a physiological calcium antagonist. It blocks the NMDA receptor channel at rest and limits calcium entry through voltage-gated channels, which is why low magnesium raises neuromuscular excitability. Roughly 50-60% of body magnesium sits in bone and most of the remainder is intracellular. Less than 1% circulates in serum, and that fraction is tightly regulated, so a normal serum magnesium does not rule out depleted tissue stores.
The clinical evidence is uneven. Magnesium is an established osmotic laxative. Meta-analyses of supplementation trials show small average reductions in blood pressure, on the order of 2 mm Hg systolic. The 2012 American Academy of Neurology and American Headache Society guideline rated magnesium as probably effective for episodic migraine prevention. Observational data link higher intake to lower type 2 diabetes risk, and glycemic benefits in trials appear mostly in people who start with low status. Trials for sleep and anxiety are small and inconsistent, and a 2020 Cochrane review concluded that magnesium is unlikely to provide meaningful prevention of idiopathic muscle cramps in older adults.
Populations at higher risk of low magnesium status include people with Crohn's disease or celiac disease, type 2 diabetes (glycosuria increases urinary magnesium loss), long-term alcohol use, and older adults. Proton pump inhibitors taken for more than a year can cause hypomagnesemia, and loop and thiazide diuretics increase urinary losses.
Forms and Bioavailability
Absorption ratings are broad tiers. Head-to-head human trials rarely support a finer ranking among well-absorbed forms.
| Form | Elemental % | Absorption | Typical dose | Cost | Labels |
|---|---|---|---|---|---|
| Magnesium Glycinatemagnesium bisglycinate, magnesium bisglycinate chelate | 14.1% | HighMagnesium bound to two glycine molecules. The chelate stays soluble across intestinal pH, and absorption proceeds through the same paracellular and TRPM6/7 channel routes as other soluble salts; head-to-head human data against citrate are limited. | 100-350 mg elemental magnesium daily | Moderate | 660 |
| Magnesium Citratetrimagnesium citrate | 16.2% | HighHighly soluble organic salt. Produced significantly higher serum and urinary magnesium than oxide in a randomized crossover trial (Kappeler 2017). | 100-350 mg elemental magnesium daily | Low | 1,343 |
| Magnesium OxideMgO | 60.3% | LowPoorly soluble at intestinal pH. Fractional absorption measured at about 4% (Firoz and Graber 2001); most of the dose stays in the gut lumen and draws water osmotically. | 400-800 mg compound for constipation; poor choice for repletion | Low | 1,361 |
| Magnesium Malatedimagnesium malate | 15.5% | HighSoluble organic salt. Human pharmacokinetic data are thin; absorption is inferred from solubility and animal studies. | 100-350 mg elemental magnesium daily | Moderate | 354 |
| Magnesium L-ThreonateMagtein, magnesium threonate | 8.3% | ModerateThreonate is a vitamin C metabolite. In rodents it raised cerebrospinal fluid magnesium more than other salts; human brain uptake has not been directly measured. | 1.5-2 g compound daily (about 104-144 mg elemental) | High | 95 |
| Magnesium Tauratemagnesium taurinate | 8.9% | ModerateOrganic salt with almost no human pharmacokinetic data; assumed to behave like other soluble organic salts. | 100-300 mg elemental magnesium daily | High | 43 |
| Magnesium Chloridemagnesium chloride hexahydrate | 12% | HighHighly soluble inorganic salt. Absorption was equivalent to lactate and aspartate and far above oxide in Firoz and Graber 2001. | 100-350 mg elemental magnesium daily | Moderate | 58 |
| Magnesium Lactatemagnesium L-lactate dihydrate | 12% | HighSoluble organic salt. Absorption was equivalent to chloride and aspartate in Firoz and Graber 2001. | 100-350 mg elemental magnesium daily | Moderate | 12 |
| Magnesium Aspartatemagnesium L-aspartate | Varies | HighSoluble organic salt. Absorption was equivalent to chloride and lactate in Firoz and Graber 2001. | 100-350 mg elemental magnesium daily | Moderate | 585 |
Labels column: number of labels in the Magnesium category that list this form. A product can list more than one form, and some labels do not state a form at all.
The number that matters is elemental magnesium, the mass of the magnesium ion itself. The carrier determines how much of each pill is magnesium, how well it dissolves, and whether the carrier has effects of its own. Oxide is 60% magnesium by weight but about 4% absorbed in the Firoz and Graber study, so its generous label figure overstates what reaches circulation. The well-absorbed organic salts (citrate, glycinate, malate, lactate, aspartate) and chloride have not been reliably ranked against each other in human trials; differences between them are smaller than the gap between any of them and oxide.
"Buffered" glycinate products blend in magnesium oxide to raise the elemental content per capsule. Threonate's brain-uptake data come from rodents, and its single human cognitive trial was small and industry funded. Topical magnesium oils and flakes have no reliable evidence of meaningful transdermal absorption.
Typical Dosing
| Group | RDA |
|---|---|
| Men 19-30 | 400 mg |
| Men 31+ | 420 mg |
| Women 19-30 | 310 mg |
| Women 31+ | 320 mg |
| Pregnancy | 350-360 mg |
| Upper limit (UL) | 350 mg per day from supplements and medications only; magnesium from food does not count toward the UL |
Supplements typically provide 100-350 mg of elemental magnesium. Doses above the UL are used deliberately as laxatives.
Food sources: pumpkin seeds, chia seeds, almonds, spinach, cashews, peanuts, black beans, edamame.
What to Look For
Read the Supplement Facts panel, not the front label. The panel lists elemental magnesium: "Magnesium (as magnesium bisglycinate chelate) 200 mg" means 200 mg of magnesium, delivered by roughly 1,400 mg of compound. Front labels sometimes advertise the compound weight instead, which makes low-dose products look strong. Check how many capsules make up the stated serving; chelates are bulky, and a 200 mg serving is often 2-4 capsules.
If the panel names more than one source, such as "(as magnesium bisglycinate, magnesium oxide)", the product is a blend and some of the dose is oxide. Third-party certification (USP Verified, NSF Certified for Sport, Informed Choice) confirms label accuracy and screens for contaminants; it does not speak to efficacy.
Red flags: proprietary blends that hide per-form amounts, "high potency" oxide marketed for repletion, and transdermal absorption claims. Green flags: a single named form, elemental milligrams per serving stated plainly, and a manufacturer willing to provide a certificate of analysis.
Magnesium Glycinate
Best general-purpose form when tolerance matters. Well absorbed and the least likely to loosen stools.
What to look for: Bisglycinate as the only form on the panel (not buffered with oxide), with elemental mg per serving stated. USP or NSF verified.
Find on iHerb Affiliate linkMagnesium Citrate
The value choice for repletion. Proven absorption advantage over oxide at a low cost per absorbed milligram.
What to look for: Capsules or tablets stating elemental mg per serving. Expect looser stools above about 200 mg per dose.
Find on iHerb Affiliate linkMagnesium Malate
A gentle, well-absorbed alternative for daytime dosing.
What to look for: Malate named alone on the panel. Avoid proprietary blends that do not state per-form amounts.
Find on iHerb Affiliate linkMagnesium L-Threonate
The only form studied for cognition, on thin and industry-funded evidence. Poor value for correcting a deficit.
What to look for: Magtein (the patented form) with about 144 mg elemental magnesium per 2 g daily serving.
Find on iHerb Affiliate linkProducts on Titrate
The Magnesium category in Titrate's index holds 4,330 labels from the NIH Dietary Supplement Label Database, 2,073 of them currently on market, out of 214,745 labels indexed in total.
Top on-market labels, ranked by label completeness and simplicity:
- Magnesium 400 mg
- Magnesium Bisglycinate Chelate
- Magnesium Malate 500 mg
- Pure Albion Magnesium 400 mg
- Chelated Magnesium
Supplement Search loads one category at a time. Choose the Magnesium tab, then type a form such as "bisglycinate" under Must contain, or a form to avoid under Must not contain.
Related Tools
- Magnesium Form Comparison
- Electrolyte Needs
- Magnesium Citrate vs Magnesium Glycinate
- Magnesium Citrate vs Magnesium Malate
- Magnesium Citrate vs Magnesium L-Threonate
- Magnesium Glycinate vs Magnesium Malate
- Magnesium Glycinate vs Magnesium L-Threonate
- Magnesium Malate vs Magnesium L-Threonate
- Magnesium Aspartate vs Magnesium Citrate
- Magnesium Aspartate vs Magnesium Glycinate
- All magnesium form comparisons
- Best Magnesium Without Oxide
- Best Magnesium Without Magnesium Stearate
- Best Magnesium Without Citric Acid
- All supplement guides
References
NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals.
Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnes Res. 2001;14(4):257-262.
Kappeler D, et al. Higher bioavailability of magnesium citrate as compared to magnesium oxide shown by evaluation of urinary excretion and serum levels after single-dose administration in a randomized cross-over study. BMC Nutr. 2017;3:7.
Pardo MR, et al. Bioavailability of magnesium food supplements: A systematic review. Nutrition. 2021;89:111294.
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.
Holland S, et al. Evidence-based guideline update: NSAIDs and other complementary treatments for episodic migraine prevention in adults. Neurology. 2012;78(17):1346-1353.
Garrison SR, et al. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev. 2020;9(9):CD009402.
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.
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