Magnesium Threonate vs Glycinate vs Citrate

Walk down any supplement aisle in the UK and you will find at least six different magnesium compounds sitting next to each other, all claiming to be the best. The three that dominate the conversation are magnesium L-threonate, magnesium glycinate (also sold as magnesium bisglycinate) and magnesium citrate. They contain the same mineral. They behave very differently once you swallow them.

If you are building a broader routine, this sits alongside our pillar guide to longevity supplements, and you can browse the full anti-ageing and longevity range. If NAD+ support is also on your list, see our NMN benefits, side effects and dosage pillar, the NMN supplements range, or NMN Pro 1000.

The short version: threonate is the form with the most direct evidence for brain outcomes, glycinate is the gentlest all-rounder for correcting low magnesium and supporting sleep, and citrate is the cheapest well-absorbed option that doubles as a mild laxative. Which one you should buy depends far more on your goal and your gut than on any marketing claim about "the most bioavailable magnesium".

This guide compares all three on absorption, elemental magnesium content, clinical evidence, cost per day, side effects and safety, using UK dosing guidance throughout.

The short answer: magnesium threonate vs glycinate vs citrate

If you only read one section, read this one.

Why the form of magnesium matters more than the label dose

Magnesium is a cofactor in hundreds of enzymatic reactions across energy production, muscle contraction, nerve signalling, blood pressure regulation and DNA repair — which is why it appears in almost every serious discussion of the hallmarks of ageing. But the mineral is never sold on its own. It is always attached to a carrier, and the carrier changes three things: how much magnesium you actually get, how much of it you absorb, and where in the body it ends up.

Elemental magnesium versus compound weight

This is where most shoppers get caught out. A capsule labelled "1,000 mg magnesium bisglycinate" does not contain 1,000 mg of magnesium. It contains 1,000 mg of the compound, of which roughly 14% is the mineral itself — about 140 mg. Threonate is even more dilute at around 8%. The percentages come straight from the molecular weights:

Notice the trap: magnesium oxide is by far the most concentrated form, and it is also the least useful. Density and absorption are not the same thing.

How magnesium is absorbed

Magnesium crosses the gut wall by two routes — a saturable, active transcellular pathway involving TRPM6/TRPM7 channels, and a passive paracellular route that handles the bulk of a larger dose. A comprehensive review by Schuchardt and Hahn in Current Nutrition & Food Science found that overall bioavailability varies widely depending on dose, the food matrix and inhibitors such as phytate and oxalate, and concluded that no single binding form has been definitively established as superior [7].

Two practical consequences follow. First, fractional absorption falls as the dose rises — splitting 300 mg into two 150 mg doses gets more into you than one 300 mg hit. Second, differences between decent organic forms are real but modest; the gulf is between organic forms and cheap magnesium oxide, not between glycinate and citrate. If you want the detail on timing and food, see our guides on taking supplements on an empty stomach and our supplement timing chart.

Magnesium L-threonate explained

Magnesium L-threonate is magnesium bound to L-threonic acid, a metabolite of vitamin C. It was developed at MIT specifically to solve one problem: getting more magnesium past the blood–brain barrier, which is tightly regulated and does not respond much to ordinary oral magnesium.

What the research actually shows

The foundational animal work

The compound first appeared in a 2010 paper in Neuron by Slutsky and colleagues, which reported that magnesium-L-threonate raised brain magnesium in rats and improved learning, working memory and both short- and long-term memory, alongside increased hippocampal synaptic density and upregulated NR2B-containing NMDA receptors [3]. This is the study every threonate product traces back to. It is also a rodent study, and it is important to say so plainly.

The human trial

The most-cited human data is the MMFS-01 trial published in the Journal of Alzheimer's Disease in 2016. It was a randomised, double-blind, placebo-controlled trial in adults aged 50–70 with self-reported cognitive complaints, dosed at roughly 25 mg/kg/day — about 1.5 g of compound for a 50–70 kg adult and 2 g for a 70–100 kg adult — over 12 weeks. The treatment group showed a significant improvement in a composite cognitive score versus placebo, and the intervention was well tolerated [1]. The caveats matter: the trial enrolled around 50 participants, and it was sponsored by the company developing the compound.

Sleep

A 2024 randomised, double-blind, placebo-controlled trial published in Sleep Medicine: X gave 80 adults aged 35–55 with self-reported sleep problems 1 g/day of magnesium L-threonate or placebo for 21 days. The magnesium group showed improvements in both questionnaire-based sleep quality and wearable-tracked sleep measures, along with better self-reported daytime energy and mood [2]. Again, industry funding applies, and 21 days is short.

Dosing and elemental content

Trial doses cluster at 1,000–2,000 mg of compound per day, which supplies roughly 80–145 mg of elemental magnesium — often less than a single glycinate capsule. That is a crucial point that marketing rarely mentions: threonate is not a good way to correct a magnesium deficiency. It is a brain-targeted intervention that happens to contain a small amount of magnesium.

Who it suits, and who it doesn't

• Good fit: adults over 45 noticing word-finding difficulty, slower recall or mental fatigue; people already meeting their magnesium needs who want a cognitive add-on; those pairing it with other nootropic-leaning supplements such as lion's mane.
• Poor fit: anyone on a budget; anyone whose actual problem is low dietary magnesium, cramps or constipation; anyone wanting a single supplement to cover general magnesium needs.

Magnesium glycinate (bisglycinate) explained

Magnesium glycinate is magnesium chelated to two glycine molecules. The chelate is stable through stomach acid and appears to be absorbed partly via dipeptide transport routes rather than competing for the standard mineral pathway — which is the mechanistic argument for why it is gentle on the gut. Glycine itself is an inhibitory neurotransmitter, which is where the "calming" reputation comes from.

What the research shows

The best recent evidence is a 2025 randomised, double-blind, placebo-controlled trial in Nature and Science of Sleep. It enrolled 155 adults aged 18–65 reporting poor sleep quality and gave them 250 mg of elemental magnesium as bisglycinate or placebo daily for four weeks. The magnesium group showed a significantly greater reduction in Insomnia Severity Index scores than placebo, though the effect size was small. Notably, exploratory analysis suggested the largest improvements occurred in participants who started with the lowest dietary magnesium intake [4].

That subgroup finding is the single most useful thing in the magnesium literature. Magnesium supplements appear to help most in people who were short of magnesium to begin with — an unglamorous conclusion that also matches a 2021 systematic review and meta-analysis of oral magnesium for insomnia in older adults, which pooled three small trials and rated the overall quality of evidence as low [5].

For a broader look at what does and doesn't move the needle on sleep, see our comparison of apigenin vs magnesium for sleep.

Dosing and elemental content

Pure magnesium bisglycinate is about 14% elemental magnesium, so 250 mg of elemental magnesium requires roughly 1,800 mg of the chelate. Many cheaper products get around this bulk by "buffering" — blending bisglycinate with magnesium oxide — which raises the elemental figure on the label while quietly lowering the quality of the product. Look for the words "fully reacted" or "not buffered", or check that the label lists no magnesium oxide at all.

Who it suits, and who it doesn't

• Good fit: almost everyone. It is the sensible default for low magnesium, trouble falling asleep, muscle tension, evening restlessness, and anyone with a sensitive gut or IBS. It is also the form we'd point to for a minimal supplement stack.
• Poor fit: people who want a laxative effect; people whose primary concern is measurable cognitive performance rather than general wellbeing.

Magnesium citrate explained

Magnesium citrate is magnesium bound to citric acid. It is highly soluble, dissociates readily and is the cheapest of the well-absorbed forms — which is why it dominates supermarket shelves.

Bioavailability: the strongest independent data

The most robust head-to-head comparison remains Walker and colleagues (2003), a randomised, double-blind, placebo-controlled trial in 46 healthy adults taking 300 mg of elemental magnesium daily as citrate, an amino-acid chelate or oxide for 60 days. Both organic forms showed significantly greater absorption than oxide by 24-hour urinary excretion, and citrate produced the highest mean serum magnesium after both acute and chronic dosing. Magnesium oxide performed no better than placebo [6].

This is worth sitting with, because it contradicts a lot of supplement marketing. In the best independent trial available, citrate — the cheap one — outperformed the chelate. The differences were not enormous, but they were in the opposite direction to what most brands claim.

The laxative effect

Unabsorbed magnesium in the bowel draws water in osmotically. At supplement doses that means softer stools; at higher doses it is a genuine laxative, and magnesium citrate is used clinically for constipation and as part of bowel preparation before colonoscopy, as listed in the BNF [9]. If you are prone to loose stools, this is a reason to choose glycinate instead. If you are prone to constipation, it is a feature rather than a bug.

Who it suits, and who it doesn't

• Good fit: budget-conscious supplementers, people with sluggish bowels, anyone building a cheap longevity stack where cost per day matters.
• Poor fit: IBS-D, anyone already prone to urgency, and anyone taking magnesium late at night who would rather not be woken up.

Magnesium threonate vs glycinate: head to head

This is the comparison most people arrive at, so let's take it goal by goal.

For sleep

Both have positive randomised trial data, and neither is dramatic. Glycinate has the larger and more recent trial (155 participants, four weeks) showing a modest reduction in insomnia severity [4]. Threonate has a smaller trial (80 participants, three weeks) showing improvements in both subjective and wearable-measured sleep [2].

Practical read: if you struggle to fall asleep or feel physically wired, start with glycinate. If you fall asleep fine but wake unrefreshed with a busy mind, threonate is the more interesting experiment. Neither is a sleeping tablet, and neither substitutes for consistent sleep timing and light exposure.

For brain fog and memory

Threonate wins by default, because it is the only form with human trials designed to measure cognition [1]. Glycinate has no comparable cognitive trial data. That said, "wins by default" is not the same as "proven" — the human evidence base is a handful of small, mostly sponsor-funded studies.

For anxiety, stress and muscle tension

Glycinate, on mechanism and tolerability, though the 2025 trial found no significant differences in secondary psychological outcomes such as perceived stress or mood [4]. Expectations should be modest.

For correcting low magnesium

Glycinate, comfortably. Per pound spent it delivers several times more elemental magnesium than threonate, and it is tolerated at higher doses. Citrate is cheaper still if your gut allows.

For cost per day

At UK prices in 2026, a threonate dose matching the trial protocol typically costs £0.70–£1.50 a day — roughly £250–£550 a year. Glycinate at a useful dose costs £55–£165 a year, and citrate less than £70. When people ask us why supplements are so expensive, threonate is exhibit A: you are paying for a patented delivery molecule, not for more magnesium. Our breakdown of longevity stack cost in the UK puts this in context.

How to choose: a simple decision framework

One more piece of advice we give constantly: change one variable at a time. If you start magnesium alongside three other new supplements, you will learn nothing about any of them. Our guide to how to start longevity supplements walks through a sensible sequencing approach, and how long supplements take to work sets realistic timelines — for magnesium, expect two to four weeks before judging sleep effects.

Can you take magnesium threonate and glycinate together?

Yes, and plenty of people do — typically glycinate in the evening and threonate split between afternoon and bedtime. The only real constraint is the total elemental magnesium, which should be counted across every product you take, including multivitamins, effervescent drinks and antacids.

A worked example: 2 g of magnesium L-threonate supplies roughly 145 mg elemental. Adding 200 mg elemental from glycinate brings the total to 345 mg — under the UK safe upper level of 400 mg from supplements, but not by a lot. Add a multivitamin containing 100 mg and you are over it.

Magnesium generally plays well with other longevity ingredients. It does not compete with NMN or NAD+ precursors, and it is a standard component of most well-built stacks — see our longevity stack guide and can you take supplements together for the interaction map. For NAD+ specifically, our pillar guide on NMN benefits, side effects and dosage is the place to start, and the full NMN supplement range is here.

Two timing points worth knowing. High-dose zinc and calcium taken simultaneously can compete with magnesium for absorption, so separate them by a couple of hours. And magnesium should be separated by at least four hours from levothyroxine, bisphosphonates, and tetracycline or quinolone antibiotics, because it binds them and reduces their absorption.

Dosage, upper limits and UK safety guidance

UK reference intakes

The NHS sets the reference nutrient intake for adults aged 19–64 at 300 mg a day for men and 270 mg a day for women, and states that most people should be able to get this from a varied diet [8]. That figure is total magnesium from all sources, food included — not a supplement target.

The safe upper level

The NHS advises that taking 400 mg or less a day of magnesium from supplements is unlikely to cause harm, and that higher short-term doses can cause diarrhoea. It also notes there is not enough evidence to know the effects of high doses taken long term [8]. The UK Expert Group on Vitamins and Minerals arrived at the same 400 mg supplemental figure; the European Food Safety Authority uses a more conservative 250 mg from supplements and fortified foods combined.

Side effects

• Common: loose stools, abdominal cramping, nausea — dose-dependent and most likely with citrate and oxide.
• Less common: a mild sedative or "heavy limbs" feeling at higher evening doses, and vivid dreams reported by some people on glycinate.
• Rare but serious: hypermagnesaemia, presenting with flushing, marked lethargy, muscle weakness, low blood pressure or irregular heartbeat. This is almost exclusively seen in people with impaired kidney function or after very large ingestions. Seek urgent medical advice if these occur.

Who should speak to a clinician first

• Anyone with chronic kidney disease or reduced kidney function — the kidneys clear excess magnesium, and impairment removes that safety valve
• People with heart block or bradyarrhythmias
• Anyone taking digoxin, diuretics, or magnesium-containing laxatives or antacids
• People with myasthenia gravis
• Anyone pregnant or breastfeeding
• Anyone with persistent symptoms that could reflect an undiagnosed condition — unexplained fatigue, palpitations or muscle weakness deserve investigation rather than a supplement

You can report a suspected side effect from any supplement or medicine to the MHRA through the Yellow Card scheme.

Quality: what to check before you buy

Magnesium is a commodity mineral, which means the difference between a good and a bad product is manufacturing quality rather than exotic ingredients. Four things to check:

1. The elemental figure. UK labels should state "magnesium bisglycinate 1,000 mg, of which magnesium 140 mg". If only the compound weight appears, the brand is hiding something.
2. Buffering. If the ingredient list contains magnesium oxide alongside bisglycinate, a meaningful share of the elemental magnesium is coming from the poorly absorbed form.
3. Third-party testing. Independent verification of identity, potency and heavy metals is the single best quality signal. See our guides to third-party tested supplements and reading a certificate of analysis.
4. Excipients. Bulky chelates need capsules, and capsules need flow agents — but there is a difference between a small amount of rice flour and a capsule that is half magnesium stearate and titanium dioxide. Our breakdown of supplement fillers explains which ones matter.

For branded threonate specifically, most UK products use Magtein, the ingredient used in the published trials. If a threonate product doesn't name its raw material source, there is no way to know whether the trial evidence applies to it.

Five magnesium myths worth ignoring

"Magnesium glycinate is 80% absorbed"

This number circulates widely and traces to nothing. Published fractional absorption figures for magnesium salts sit in the single digits to low double digits, with the dose itself being the dominant variable [7]. Any brand quoting 80–90% absorption is quoting marketing, not data.

"Threonate is the most bioavailable magnesium"

Threonate's claim is about where magnesium goes, not how much is absorbed. On elemental magnesium delivered per gram of product, it is the weakest of the three forms discussed here.

"Everyone is magnesium deficient"

Frank deficiency is uncommon in people with normal kidney function eating a varied diet. Suboptimal intake is more common than deficiency, and the two are not the same clinical situation. Serum magnesium is also a poor marker of body stores, which is why routine testing is rarely helpful.

"You must take magnesium at night"

There is no absorption reason to. Evening dosing is popular because of the sedating feel, not because timing changes uptake. If a dose upsets your stomach, taking it with food helps. Our supplement timing chart covers the forms where timing genuinely matters.

"More magnesium means better sleep"

The trial data points the other way: benefits were largest in people who started with the lowest intake [4]. Pushing the dose above the safe upper level buys diarrhoea, not deeper sleep.

Frequently asked questions

Is magnesium threonate better than glycinate?

Not universally. Threonate is better if your goal is cognitive — memory, focus, mental clarity — because it is the only form with human trials designed around brain outcomes. Glycinate is better for correcting low magnesium, muscle tension and sleep onset, and it costs roughly a fifth as much per day. For most people, glycinate is the better first purchase.

Can I take magnesium threonate and glycinate at the same time?

Yes. Many people take threonate during the day and glycinate in the evening. Add up the elemental magnesium across all products and keep the total at or below 400 mg a day from supplements, in line with NHS guidance.

Which magnesium is best for sleep?

Magnesium glycinate has the largest randomised trial support, with 250 mg of elemental magnesium daily producing a modest but statistically significant reduction in insomnia severity over four weeks. Threonate has smaller trials showing improvements in both subjective and device-measured sleep. Benefits in both cases are modest and appear strongest in people with low baseline magnesium intake.

Which magnesium is best for anxiety?

Glycinate is the usual recommendation because glycine is itself an inhibitory neurotransmitter and the form is well tolerated at higher doses. Trial evidence for anxiety and mood outcomes specifically is weak — the 2025 bisglycinate trial found no significant differences in secondary psychological measures. Magnesium is not a treatment for an anxiety disorder; if anxiety is affecting your daily life, speak to your GP.

How much magnesium threonate should I take daily?

Published trials used approximately 25 mg of compound per kg of body weight per day: 1.5 g daily for people weighing 50–70 kg and 2 g daily for 70–100 kg, usually split into two doses. That supplies roughly 110–145 mg of elemental magnesium.

Does magnesium citrate really cause diarrhoea?

It can. Unabsorbed magnesium draws water into the bowel osmotically, which is precisely why magnesium citrate is used as a laxative and in bowel preparation. At 100–200 mg of elemental magnesium most people are fine; above 300–400 mg, loose stools become common. Splitting the dose and taking it with food reduces the effect.

Is magnesium glycinate the same as magnesium bisglycinate?

In practice, yes. "Bisglycinate" is the chemically precise term — one magnesium ion bound to two glycine molecules. UK and US labels use the terms interchangeably. What actually differs between products is whether the chelate is fully reacted or buffered with magnesium oxide.

How long does magnesium take to work?

Gut effects are immediate. Sleep and muscle effects, where they occur, generally take two to four weeks of consistent daily use. Cognitive trials with threonate measured outcomes at six and twelve weeks. Judge any magnesium supplement over a month, not a night.

Can you take too much magnesium?

Yes. The NHS advises keeping supplemental magnesium at 400 mg a day or less, and notes that higher doses can cause diarrhoea over the short term. Serious toxicity (hypermagnesaemia) is rare in people with healthy kidneys but is a real risk in chronic kidney disease. Magnesium from food does not carry this risk.

Which magnesium is best for women over 40?

Glycinate is the usual starting point, because the common complaints in this group — disturbed sleep, muscle tension, low-grade fatigue — respond best to simply having adequate magnesium, and glycinate delivers that most comfortably. Threonate is worth adding if cognitive symptoms are prominent. Our guides to longevity supplements for women over 40 and longevity supplements for men over 50 put magnesium in the context of a full routine.

References

1. Liu G, Weinger JG, Lu ZL, Xue F, Sadeghpour S. Efficacy and safety of MMFS-01, a synapse density enhancer, for treating cognitive impairment in older adults: a randomized, double-blind, placebo-controlled trial. Journal of Alzheimer's Disease. 2016;49(4):971–990. https://pubmed.ncbi.nlm.nih.gov/26519439/
2. Hausenblas HA, Lynch T, Hooper S, Shrestha A, Rosendale D, Gu J. Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems: a randomized controlled trial. Sleep Medicine: X. 2024;8:100121. https://www.sciencedirect.com/science/article/pii/S2590142724000193
3. Slutsky I, Abumaria N, Wu LJ, et al. Enhancement of learning and memory by elevating brain magnesium. Neuron. 2010;65(2):165–177. https://pubmed.ncbi.nlm.nih.gov/20152124/
4. Schuster J, Cycelskij I, Lopresti A, Hahn A. Magnesium bisglycinate supplementation in healthy adults reporting poor sleep: a randomized, placebo-controlled trial. Nature and Science of Sleep. 2025;17:2027–2040. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12412596/
5. Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complementary Medicine and Therapies. 2021;21(1):125. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8053283/
6. Walker AF, Marakis G, Christie S, Byng M. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium Research. 2003;16(3):183–191. https://pubmed.ncbi.nlm.nih.gov/14596323/
7. Schuchardt JP, Hahn A. Intestinal absorption and factors influencing bioavailability of magnesium — an update. Current Nutrition & Food Science. 2017;13(4):260–278. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5652077/
8. NHS. Vitamins and minerals — Others (magnesium). https://www.nhs.uk/conditions/vitamins-and-minerals/others/
9. NICE / British National Formulary. Magnesium citrate: indications and dose. https://bnf.nice.org.uk/drugs/magnesium-citrate/
10. National Institutes of Health, Office of Dietary Supplements. Magnesium — Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/
11. Allen MJ, Sharma S. Magnesium. StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK519036/
12. Schwalfenberg GK, Genuis SJ. The importance of magnesium in clinical healthcare. Scientifica. 2017;2017:4179326. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5637834/
13. Kirkland AE, Sarlo GL, Holton KF. The role of magnesium in neurological disorders / magnesium therapy in learning and memory. Magnesium in the Central Nervous System, NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK507270/
14. Alzheimer's Drug Discovery Foundation, Cognitive Vitality. Magnesium: report for researchers. https://www.alzdiscovery.org/uploads/cognitive_vitality_media/Magnesium-Cognitive-Vitality-For-Researchers.pdf
15. MHRA. Yellow Card scheme: reporting suspected side effects. https://yellowcard.mhra.gov.uk/