- Magnesium acts as a cofactor in more than 300 enzyme systems, including the ones that run energy metabolism, muscle contraction and nerve signalling.
- The only number that matters on a magnesium label is elemental magnesium. The weight of the compound is not the weight of the mineral.
- Bisglycinate is about 14 percent elemental magnesium by weight, citrate about 16 percent, oxide about 60 percent. Oxide is also the least absorbed of the three.
- Glycinate is chosen for tolerance rather than for a larger number on the front of the pack.
- The sleep evidence is early rather than settled: small trials, mostly in older adults, mostly measuring how people say they slept.
- For adults, 350 mg a day is the upper limit for magnesium taken from supplements. That limit exists because of the laxative effect.
Magnesium is the mineral most people meet through a symptom. A cramp at night, a jaw that will not unclench, sleep that arrives late and leaves early. Then they read a pack, see a large number on the front, and buy the largest one. That is usually where the arithmetic goes wrong.
This page is about the arithmetic. What magnesium does, which part of the label is real, how the forms differ, and what the published evidence does and does not support.
What magnesium actually does
Magnesium is a cofactor in more than 300 enzyme systems. In plain terms, it sits inside reactions rather than doing something on its own. It is required by the enzymes that handle adenosine triphosphate, the molecule your cells spend to do work, which is why magnesium appears in every description of energy metabolism. It also takes part in moving calcium and potassium across cell membranes, which is how it ends up involved in muscle contraction, muscle relaxation and nerve signalling.1
About half to sixty percent of the magnesium in an adult body sits in bone. Most of the rest is inside soft tissue. Less than one percent circulates in blood, which is why a normal serum magnesium result does not tell you much about your intake, and why an honest reading of the science stays careful about who is actually short of it.1
Elemental magnesium is the number behind the number
Magnesium is never sold as magnesium. It is sold as a salt or a chelate, which means magnesium plus a carrier. The mineral is only a fraction of that total weight, and the fraction changes with the form.
Those percentages come from molecular weight, not from marketing. Magnesium has an atomic weight near 24. Magnesium bisglycinate weighs near 172 as a molecule, so the mineral is roughly one seventh of it and the rest is glycine. Magnesium oxide is a small molecule, so the mineral is a large share of it, and yet oxide has the weakest absorption record of the common forms. That is the paradox of this category: the biggest elemental number is often attached to the form that delivers least.2, 6
So a compound weight printed on the front of a pack is not a dose. Two products can both print 2000 mg and deliver very different amounts of magnesium. Our position is that both numbers belong on the pack, side by side, with the elemental figure stated in milligrams.
The form path
Oxide is the cheapest way to put a large elemental number on a label. It is also poorly absorbed, and what is not absorbed stays in the gut and draws water in, which is why it doubles as a laxative.2
Citrate is the better documented step up. In small comparative studies it was absorbed more readily than oxide, and it remains a reasonable, well referenced choice.2, 3
Bisglycinate binds magnesium to two molecules of glycine. The case for it is tolerance. At a given elemental dose it is generally gentler on the stomach, and that matters, because the most common reason people stop taking magnesium is not that it failed, it is that it upset them. The case against overstating it is that head to head human absorption data on glycinate specifically is still thin next to citrate.6
What the evidence says about sleep
What exists. Small randomised trials in older adults with insomnia have reported improvement in subjective sleep measures after magnesium supplementation. A separate small literature on glycine taken before bed reports better self rated sleep quality.4
What does not exist. Large, long, well powered trials in healthy adults using objective sleep measurement. Most of the work is short, small, and relies on questionnaires rather than sleep laboratory data.
Honest reading. Magnesium is a reasonable input to a sleep routine, particularly where intake is low. It is not a sedative and we will not describe it as one.
What the evidence says about muscle and recovery
What exists. Magnesium is required for normal muscle contraction and relaxation, and low magnesium status is associated with neuromuscular excitability.1
What does not exist. Good evidence that magnesium prevents cramp in most people. A Cochrane review concluded that magnesium is unlikely to provide meaningful cramp prophylaxis in older adults, and the evidence in exercise associated cramp is weaker still.5
Honest reading. Correcting a low intake is worth doing on its own terms. Treating magnesium as the answer to every cramp is not supported by the trials.
How much, and when
Reference intakes are set for total magnesium, from food and supplements together. The United States reference intake for adults is 400 to 420 mg a day for men and 310 to 320 mg a day for women, and it rises in pregnancy.1 Most adults already get part of that from food. Whole grains, legumes, nuts, seeds and leafy greens are the usual sources, and a diet built on refined grains supplies noticeably less.
The number that constrains a supplement is a different number. The tolerable upper intake level for magnesium from supplements alone is 350 mg a day for adults, and it exists because higher supplemental doses commonly cause loose stools.1 A sensible supplemental range for most adults sits under that ceiling, taken with food, and split across the day if the elemental dose is on the higher side.
On timing, there is no strong trial evidence that an evening dose works better than a morning one. Evening suits the routine most people are trying to build, and the routine is what makes any supplement work. Give a change three to four weeks before you judge it.
Who should be careful
Magnesium is cleared by the kidneys, so reduced kidney function is the main reason to take medical advice before supplementing at all. Magnesium can also interfere with the absorption of some medicines, including tetracycline and quinolone antibiotics and oral bisphosphonates, which is why those are usually spaced at least two hours apart from a magnesium dose.1 If you are pregnant, nursing, on prescription medication, or managing a diagnosed condition, that is a conversation for your physician rather than for a label.
How to read a magnesium label
- Find the elemental magnesium figure in milligrams. If it is not printed, the pack has not told you the dose.
- Check the form. Oxide, citrate, bisglycinate, malate and threonate are not interchangeable.
- If a blend is used, look for the split. A blend that lists only a total is a blend you cannot evaluate.
- Read the serving size. Per serving and per tablet are different numbers and they are often printed close together.
- Compare the elemental figure against the 350 mg supplemental ceiling, not against the food based reference intake.
Questions we get
Is glycinate better than citrate?
Better tolerated, usually. Better absorbed, not proven head to head. Citrate has the older and larger absorption literature. Glycinate has the stronger practical record for people staying on it.
Why is the compound weight so much larger than the magnesium?
Because a chelate carries its carrier. Two glycine molecules weigh more than the mineral they hold, so most of the compound weight is glycine, not magnesium.
Will magnesium make me sleepy?
It is not a sedative. Some people report falling asleep more easily, particularly if their intake was low. Others notice nothing.
Can I take it with calcium or zinc?
Yes, and many formulas combine them. Very high doses of zinc can interfere with magnesium balance, so add up your total intake across every product you take.
What happens if I take too much?
The first sign is almost always the gut: loose stools or cramping. That is the reason for the 350 mg supplemental ceiling in adults.
We do not have large, long trials comparing bisglycinate directly against citrate for absorption, or for sleep outcomes in healthy adults. Any claim that one form is decisively superior is ahead of the data. We also do not have a simple, reliable test of magnesium status, because serum magnesium is a poor marker of body stores. That means nobody, including us, can tell you from a blood report alone whether you need this.
The glycine story is genuinely interesting and genuinely unfinished. The trials that report better self rated sleep used glycine on its own, at around 3 g before bed, which is more glycine than a typical magnesium bisglycinate dose delivers. We do not extend those findings to our own product, and we will not until the actual dose is tested.
- National Institutes of Health, Office of Dietary Supplements. Magnesium: fact sheet for health professionals.
- Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnesium Research, 2001.
- 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.
- Abbasi B, Kimiagar M, Sadeghniiat K, et al. The effect of magnesium supplementation on primary insomnia in elderly: a double blind placebo controlled clinical trial. Journal of Research in Medical Sciences, 2012.
- Garrison SR, Korownyk CS, Kolber MR, et al. Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews, 2020.
- Schuchardt JP, Hahn A. Intestinal absorption and factors influencing bioavailability of magnesium: an update. Current Nutrition and Food Science, 2017.