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What does magnesium do?

Magnesium is a mineral involved in hundreds of enzyme reactions, including the ones that release energy from food and the signalling that makes muscle contract and relax. The Australian Nutrient Reference Values set the recommended dietary intake at 400 to 420 mg a day for adult men and 310 to 320 mg for adult women. Food sources are mostly green vegetables, legumes, nuts, seeds and wholegrains.

Supplements come in several forms and the form changes how well it is absorbed and how it sits. Magnesium oxide is cheap and common but poorly absorbed, and it is the one most likely to loosen the bowels. Citrate, glycinate and bisglycinate absorb better and are gentler. Glycinate in particular is the usual choice for evening use because glycine itself is calming.

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How it is usually used

Most labels suggest a dose in the evening, since that suits the muscle relaxation and sleep uses people buy it for. Take it with food if it unsettles your stomach. If you get loose bowels, that is usually a sign of too much at once or an oxide form, and splitting the dose or switching form generally fixes it. Supplements are not a substitute for medical advice. If you are pregnant or breastfeeding, take prescription medication, or are managing a health condition, check with your doctor or pharmacist before starting something new.

Frequently asked questions

Which form of magnesium is best?

It depends what you want from it. Glycinate and bisglycinate absorb well and are gentle on the stomach, which makes them the usual pick for evening and sleep use. Citrate absorbs well and has a mild laxative effect some people want. Oxide is the cheapest but the least absorbed. Threonate is marketed for cognition and costs considerably more.

How much magnesium should I take?

The recommended dietary intake is 400 to 420 mg a day for adult men and 310 to 320 mg for adult women, and that total includes what you eat. Supplement doses commonly supply 100 to 400 mg of elemental magnesium. Read the elemental figure rather than the compound weight, since 1,000 mg of magnesium citrate is nowhere near 1,000 mg of magnesium.

Does magnesium help with sleep?

It is one of the most common reasons people buy it, and magnesium does play a role in nervous system regulation. The evidence is stronger for people who are low in magnesium than for those who are already getting enough. Glycinate is the usual form chosen for this because glycine has its own calming properties.

Will magnesium stop my cramps?

Sometimes, though the evidence is mixed and cramp has several possible causes. If your intake is low, correcting that is reasonable and worth trying. If your diet already supplies plenty, magnesium is less likely to be the answer, and hydration, sodium and training load are worth looking at instead.

Why does magnesium upset my stomach?

Usually the form or the dose. Magnesium oxide and citrate both draw water into the bowel, which is why they can loosen things at higher doses. Switching to glycinate, splitting the dose across the day, or taking it with food generally resolves it.

Sources

Last reviewed: 10 October 2026