Magnesium and Sleep: What a New Trial Actually Found

Magnesium and Sleep: What a New Trial Actually Found — Proco

Magnesium for sleep is one of the most-searched supplement questions there is — and most of what gets written about it doesn't cite an actual trial. Here's one, published in Nature and Science of Sleep in August 2025.

The trial

155 adults aged 18–65 reporting poor sleep quality took either magnesium bisglycinate or a matched placebo nightly for four weeks, in a randomized, double-blind, placebo-controlled design. The active dose was 250mg of elemental magnesium per day, delivered as two capsules of 893mg magnesium bisglycinate each. Because bisglycinate is magnesium bonded to glycine, that same dose also delivered 1,523mg of glycine — the trial paper reports this explicitly (125mg magnesium and 761.5mg glycine per capsule). The glycine was not a second ingredient added alongside the magnesium; it is what the chelate is made of.1

The result

The primary outcome was the Insomnia Severity Index. Scores fell further on magnesium than on placebo: −3.9 points (95% CI −5.8 to −2.0) versus −2.3 points (95% CI −4.1 to −0.4), p = 0.049. That clears the conventional significance threshold, but only just. Expressed as a percentage of baseline, the magnesium group improved 28% and the placebo group 18% over the four weeks — both of those within-group changes were themselves significant at p = 0.001, which is a useful reminder of how much of this kind of improvement happens on placebo alone.

p = 0.049
The between-group p-value for the primary outcome: a 1.6-point greater fall in Insomnia Severity Index on magnesium bisglycinate than placebo over four weeks, effect size Cohen's d = 0.2. Real, significant, and about as small as a significant result gets.1
Correction, September 2026: An earlier version of this article dated the trial to 2026, described the intervention as "250mg of elemental magnesium (as bisglycinate) plus 1,523mg of glycine," and presented the 28%-versus-18% figures as the statistically significant comparison. Three fixes. The trial was published in August 2025. The glycine was not added on top of the magnesium — it is the ligand inside the bisglycinate salt. And the 28% and 18% figures are within-group changes from baseline; the between-group result was −3.9 versus −2.3 ISI points at p = 0.049. Attaching "statistically significant" to the 28-versus-18 framing made the effect look larger and cleaner than it was, so we have replaced it with the actual between-group numbers.

Why magnesium and glycine are plausible candidates

Neither part of that molecule was picked at random. Magnesium is a cofactor the nervous system leans on to keep itself from over-firing. A 2025 mechanistic review in Nature and Science of Sleep lays out two specific pathways: magnesium potentiates GABA-A receptor activity, which is the brain's main inhibitory signaling system and the same receptor family targeted by prescription sedatives, and it acts as a voltage-dependent blocker of NMDA receptors, damping the excitatory glutamate signaling that can keep a wired brain from downshifting at night.2 Put simply: more GABA-A activity and less NMDA activity both point the nervous system toward calm, which is the physiological state sleep onset requires. It is also why magnesium keeps turning up in the anxiety literature, where the evidence is thinner than the marketing.

Glycine has its own, separate line of human evidence. In a randomized, double-blind crossover study, adults with sleep complaints who took 3g of glycine before bed reported better subjective sleep quality, and the improvement correlated with polysomnographic changes in their recorded sleep architecture, not just self-report.3 A related trial from the same research group found the same 3g dose significantly reduced next-day fatigue and improved psychomotor vigilance performance in volunteers whose sleep had been cut by 25% for three consecutive nights — though daytime sleepiness itself only trended in that direction without reaching significance.4 One proposed mechanism is that glycine helps lower core body temperature around bedtime, which is itself part of the body's natural sleep-onset signal.

Because bisglycinate delivers magnesium and glycine inseparably, this trial cannot tell you how much of the improvement came from the mineral and how much from the amino acid.

That's the honest limitation worth stating plainly, and the trial authors say as much themselves — they note the glycine's "co-presence may produce synergistic effects." It is not a flaw in the study; it is intrinsic to the molecule. Anyone taking any magnesium bisglycinate product is taking both. What no trial has done is separate them, or compare bisglycinate against an equivalent elemental dose of a non-glycine magnesium form on sleep outcomes.

The honest size of the effect

The effect size was small: Cohen's d = 0.2. No other psychological outcome — the questionnaires covering mood and wellbeing — differed significantly between groups. This is a real, modest effect on one specific measure, insomnia severity, not evidence of a broader transformation in how people felt during the day. The authors did report one exploratory signal worth flagging as exploratory: participants who reported lower baseline dietary magnesium intake appeared to improve more, which the paper frames as a possible high-responder subgroup requiring proper testing rather than a finding. It is also worth knowing who made what: the study supplement was manufactured by Biogena, and one of the four authors is the managing director of a contract research organisation that takes nutraceutical-industry funding.

Is this result typical, or an outlier?

It's worth checking this trial against the wider magnesium-and-sleep literature, since a single study sitting on its own is easy to either oversell or dismiss. A separate, earlier randomized, double-blind, placebo-controlled trial gave 46 elderly adults with primary insomnia 500mg of magnesium daily for eight weeks. It also found a statistically significant improvement in Insomnia Severity Index score (p = 0.006), along with improved sleep efficiency (p = 0.03), sleep onset latency (p = 0.02) and sleep-log sleep time (p = 0.002), plus favorable shifts in serum melatonin (p = 0.007) and cortisol (p = 0.008).5 The nulls in that trial deserve equal billing: total sleep time did not differ significantly between groups (p = 0.37), and neither early-morning awakening (p = 0.08) nor — awkwardly, for a magnesium trial — serum magnesium concentration (p = 0.06) reached significance. The population, dose, and duration all differ from the 2025 trial, so the two aren't directly comparable, but the direction and the general modesty line up.

Pooling the field gives the same picture. A systematic review of three RCTs in 151 older adults found sleep onset latency 17.36 minutes shorter on oral magnesium than placebo (95% CI −27.27 to −7.44, p = 0.0006), while total sleep time improved 16.06 minutes and was not statistically significant — with all three trials at moderate-to-high risk of bias and the evidence graded low to very low quality.6 If you want the form-by-form version of this argument, it's in glycinate vs citrate vs threonate.

Key takeaway: Independently-run trials using different magnesium doses and forms in different populations keep finding a statistically significant — but modest — improvement in insomnia severity and time-to-sleep specifically. None found a broad daytime-functioning boost, and the pooled evidence is graded low quality. That combination of "real but bounded" is the honest read of where the evidence currently sits.

Why the form of magnesium matters

The 2025 trial used magnesium bisglycinate, and that choice isn't incidental. Magnesium salts differ substantially in how well they're absorbed and how well people tolerate them. A controlled comparison of magnesium citrate against magnesium oxide — one of the cheapest and most common forms on supplement shelves — found citrate produced a significantly larger rise in urinary magnesium excretion after dosing, a marker of how much was actually absorbed, while oxide performed poorly by comparison.7 Bisglycinate has never been compared head-to-head with citrate on absorption, so we won't claim it matches or beats it. What it does have is an isotope study showing faster and larger uptake than oxide, and better tolerability in every patient tested.8 That matters for a sleep supplement specifically: a form that causes GI discomfort before bed works against the goal, regardless of what's happening at the GABA-A receptor. We go deeper into that trade-off in why we chose this form.

What this means in practice

If someone's main complaint is difficulty falling asleep, this trial is a reasonable evidence basis for magnesium bisglycinate at this dose. If the goal is more energy or a better mood during the day, this particular trial doesn't support that — a different mechanism, or a different intervention, would be doing that work. And the timing question people ask next has its own answer: see morning or night and how long it actually takes to notice anything. For anyone whose sleep problem has lasted months, the intervention with far better evidence than any supplement is CBT-I, and we'd rather say so than sell around it.

What we take from this

We dose magnesium (glycinate form) in the range this and other sleep-focused trials tested. We describe the effect the way the trial describes it: real, modest, at p = 0.049, and specific to insomnia severity — not a cure for poor sleep. On the product side, Proco's Magnesium Glycinate delivers 275mg elemental magnesium from 2,500mg of magnesium glycinate across three capsules, third-party tested every batch. That sits slightly above the elemental magnesium dose used in this trial, and because it is the same class of chelate, the glycine comes bound in rather than being absent — most of that 2,500mg is the glycine ligand. We don't declare a separate glycine figure on our label, so we won't put a number on it here, and we're not claiming our product reproduces this trial's exact protocol. But it isn't a magnesium-only product either, and an earlier version of this article wrongly implied that it was.

This article is for informational purposes only and has not been evaluated by the FDA. It is not intended to diagnose, treat, cure, or prevent any disease, including insomnia. Speak with a healthcare provider before starting any new supplement, especially if you take medication or have an existing health condition.

References

  1. Schuster J, Cycelskij I, Lopresti A, Hahn A (2025). Magnesium bisglycinate supplementation in healthy adults reporting poor sleep: a randomized, placebo-controlled trial. Nature and Science of Sleep, 17:2027–2040. pubmed.ncbi.nlm.nih.gov/40918053
  2. He C, Wang B, Chen X, Xu J, Yang Y, Yuan M (2025). The Mechanisms of Magnesium in Sleep Disorders. Nature and Science of Sleep. dovepress.com/the-mechanisms-of-magnesium-in-sleep-disorders
  3. Yamadera W, Inagawa K, et al. (2007). Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep and Biological Rhythms. onlinelibrary.wiley.com/doi/10.1111/j.1479-8425.2007.00262.x
  4. Bannai M, Kawai N, Ono K, Nakahara K, Murakami N (2012). The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Frontiers in Neurology, 3:61. pubmed.ncbi.nlm.nih.gov/22529837
  5. Abbasi B, Kimiagar M, Sadeghniiat K, Shirazi MM, Hedayati M, Rashidkhani B (2012). The effect of magnesium supplementation on primary insomnia in elderly: a double-blind placebo-controlled clinical trial. Journal of Research in Medical Sciences. pubmed.ncbi.nlm.nih.gov/23853635
  6. Mah J, Pitre T (2021). Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complementary Medicine and Therapies, 21:125. link.springer.com
  7. Lindberg JS, Zobitz MM, Poindexter JR, Pak CY (1990). Magnesium bioavailability from magnesium citrate and magnesium oxide. Journal of the American College of Nutrition. pubmed.ncbi.nlm.nih.gov/2407766
  8. Schuette SA, Lashner BA, Janghorbani M (1994). Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection. JPEN, 18(5):430–435. pubmed.ncbi.nlm.nih.gov/7815675

Related reading

Proco Magnesium Glycinate is dosed at 275mg elemental magnesium from 2,500mg magnesium glycinate across three capsules, third-party tested every batch. Shop Magnesium →