TL;DR

• Magnesium is involved in over 300 enzyme systems, including muscle and nerve function, so the form matters less for whether it's "real" magnesium and more for how much your body actually absorbs and how your gut handles it.
• Magnesium oxide is common but relatively poorly absorbed compared with more soluble forms, and it is also more likely to cause gastrointestinal effects such as diarrhoea.
• Magnesium citrate absorbs better than oxide but can still have a laxative effect in some people.
• Magnesium bisglycinate (magnesium bound to the amino acid glycine) is a chelated form with evidence of good absorption, and is commonly chosen when gastrointestinal tolerability is a priority.
• Magnesium is studied across several areas relevant to women, including muscle cramps, sleep and bone health, although the strength of evidence varies considerably by outcome and magnesium form.
• We use magnesium bisglycinate in both our AM and PM sachets of our Prenatal Core.

Magnesium supplements aren't interchangeable just because they all say "magnesium" on the label. The mineral is always bound to something else, oxide, citrate, glycine, and the accompanying compound can influence solubility, absorption and gastrointestinal tolerability. For something taken daily, often for years, that difference matters more than it might seem.

What magnesium actually does

Magnesium is a cofactor for more than 300 enzyme systems in the body, including energy production, muscle contraction and relaxation, and nerve signalling. Around 60% of the body's magnesium is stored in bone. Requirements and typical intake shift at different life stages, rising in pregnancy. Magnesium handling may also change after menopause, older human studies found higher urinary magnesium excretion after menopause, and reductions in urinary magnesium loss when women were given oestrogen therapy.

Why the form matters

Magnesium oxide is a common supplemental form. It is poorly soluble and relatively poorly absorbed compared with more soluble forms such as citrate. A comparison of magnesium citrate and magnesium oxide found citrate produced a substantially larger rise in urinary magnesium after an oral dose, a marker of how much was actually absorbed, while oxide showed almost none. At higher supplemental doses, oxide is also more likely to cause gastrointestinal effects such as diarrhoea.

Magnesium citrate absorbs considerably better than oxide and is a reasonable choice, but like other soluble magnesium salts it can have a laxative effect in some people.

Magnesium bisglycinate (also called magnesium glycinate) is magnesium chelated to two molecules of the amino acid glycine. In patients with ileal resection and impaired magnesium absorption, a small controlled study found similar overall absorption from magnesium diglycinate and oxide (23.5% vs 22.8%), but diglycinate performed substantially better in the subgroup of patients with the poorest oxide absorption, and was better tolerated overall. That population is quite different from the general population, so the result doesn't automatically generalise.

Where magnesium comes up for women, at different stages

Muscle cramps are one of the more commonly studied use cases, and pregnancy happens to be where the best-quality trial sits. A randomised, placebo-controlled trial using magnesium bisglycinate chelate specifically, 300 mg a day for four weeks in 86 pregnant women, found a significantly greater reduction in both cramp frequency (86.0% vs 60.5%) and cramp intensity (69.8% vs 48.8%) compared with placebo. That's a promising, specific result, not proof that every magnesium form works equally well for cramps generally. Other trials, mostly using citrate or lactate, have found no meaningful benefit over placebo, and a Cochrane review has described the evidence for magnesium and leg cramps in pregnancy as genuinely unresolved. Most of the controlled trial evidence discussed here happens to be in pregnant women rather than women more broadly.

Bone health is one area where magnesium has been studied in postmenopausal women, when bone density loss accelerates as oestrogen falls. A small trial in postmenopausal women with osteoporosis found 30 days of oral magnesium citrate reduced a marker of bone breakdown, and separately, a meta-analysis pooling several studies found postmenopausal women with osteoporosis tended to have lower blood magnesium than those without it. Worth being precise about what this does and doesn't show: the trial was small, short and not blinded against a placebo, and the meta-analysis is observational, so it can't say low magnesium causes bone loss, only that the two tend to appear together. It's a genuinely interesting area, not a settled one.

Sleep is worth a direct mention here since it's specifically the form we use. A 2025 randomised, double-blind, placebo-controlled trial gave 155 adults with self-reported poor sleep either 250 mg of elemental magnesium as bisglycinate or a placebo for four weeks. The magnesium group had a significantly greater reduction in insomnia severity scores, although the difference compared with placebo was modest. The broader magnesium-and-sleep literature fits that same cautious picture: a systematic review found relatively consistent observational associations between magnesium status and sleep quality, but randomised supplementation trials overall have been less consistent. A separate, well-publicised sleep trial used a different form, magnesium L-threonate, and found improvements in sleep quality and daytime functioning, worth knowing about, but that result doesn't transfer to bisglycinate or any other magnesium form on the strength of that trial alone.

Why we use magnesium bisglycinate

Given the choice between a relatively poorly absorbed form such as oxide and a chelated form with evidence supporting good absorption and practical tolerability, bisglycinate was the more sensible fit for something meant to be taken daily over the long term. It's the form we use in both our AM and PM sachets.

This article is for general educational purposes and isn't medical advice. Please consult a doctor or dietitian about your individual magnesium needs, particularly if you have kidney disease or are taking medication that interacts with magnesium.

Sources

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