Magnesium: when a supplement makes sense and when it does not

General information, not medical advice. If you have kidney disease, take medication or are considering a supplement for persistent symptoms, talk to your GP or pharmacist.

Magnesium is a mineral your body needs for your muscles, nerves and bones, among other things. This article explains how much you need, where it is found, what research says about cramps and when a supplement does or does not make sense.

How much magnesium you need

In its 2015 opinion, the European Food Safety Authority (EFSA) set an adequate intake of 350 milligrams a day for men and 300 milligrams a day for women. EFSA assumes that amount is enough for almost everyone; it is not a minimum below which you are immediately deficient.

Magnesium is found in many everyday foods: wholemeal bread and other whole grains, pulses, nuts and seeds, green leafy vegetables and dark chocolate. Water and coffee provide some too. If you eat a varied diet with plenty of plant foods, you usually get a good amount. The article on high-protein meals without meat or fish describes that kind of diet.

When a deficiency can develop

A real deficiency is unusual in healthy people. It can develop with persistent diarrhoea or vomiting, some bowel diseases, heavy drinking and certain medicines, such as some diuretics or stomach acid reducers used for a long time. You cannot tell from how you feel. Your GP can order a blood test if there is a reason.

Magnesium for cramps?

Magnesium is often promoted for muscle cramps, poor sleep and stress. For cramps there is a good review: a 2020 Cochrane review by Garrison and colleagues pooled randomised trials on magnesium for muscle cramps. The researchers conclude that in older adults with night-time leg cramps without a clear cause, magnesium is unlikely to have a noticeable effect. In pregnant women the evidence was conflicting. The article on how to read a supplement label helps you look critically at claims on packaging.

For sleep and stress there is no comparable review showing a clear effect. If you sleep badly, it pays to look at the cause first, such as your sleep rhythm, caffeine late in the day or worrying, rather than reaching for a jar straight away.

Supplements and their labels

If you do choose a supplement, packaging lists different forms, such as magnesium oxide, magnesium citrate or magnesium bisglycinate. These are compounds of magnesium with another substance. Check on the label whether the stated amount refers to the magnesium itself or to the whole compound, because that can make a big difference to what you actually get.

More is not better

Magnesium from ordinary food causes no problems. Supplements are different: too much at once can cause diarrhoea. European experts therefore set a safe upper limit of 250 milligrams a day for magnesium from supplements and fortified foods, on top of what you get from ordinary food. If you have kidney disease, your body is less able to get rid of excess magnesium and a supplement is not without risk. If you already take other supplements or medicines, ask your pharmacist whether the combination is fine, because magnesium can affect how some medicines are absorbed.

References

• EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on Dietary Reference Values for magnesium. EFSA Journal. 2015;13(7):4186.
• European Food Safety Authority. Tolerable upper intake levels for vitamins and minerals. Scientific Committee on Food en NDA Panel. 2006.
• Garrison SR, Korownyk CS, Kolber MR e.a. Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews. 2020;(9):CD009402.