What magnesium does – and the claims the evidence doesn’t back
What magnesium does for muscles, nerves and bones is well supported, but a Cochrane review found it unlikely to stop cramps, and sleep evidence is still limited.
Magnesium is a mineral the body needs to work properly, and it is especially important for a healthy heart, nerves, muscles and bones, according to Harvard Health Publishing. It takes part in more than 300 chemical reactions in the body and helps regulate calcium and blood sugar levels.
The NHS says adult men need 300mg of magnesium a day. Adult women need 270mg a day, and most people should be able to get all they need from a varied, balanced diet, the NHS adds. Both figures apply to the 19 to 64 age group.
Good sources include spinach, nuts and wholemeal bread, the NHS says. Harvard Health lists green, leafy vegetables, beans, whole grains, pumpkin seeds and bananas among foods that supply the mineral.
Magnesium deficiency is common among adults over 70, Harvard Health says, with low intake, poor absorption, certain medicines and kidney disease among the causes.
The cramp claim
Magnesium supplements are often sold as a remedy for muscle cramps, but the evidence does not support this for most people. A 2020 Cochrane review by Garrison and colleagues, which looked at 11 trials involving 735 people, found it unlikely that magnesium supplementation provides clinically meaningful relief from skeletal muscle cramps in older adults, at any dose or way of taking it. Differences in cramp frequency between magnesium and a placebo were small and not statistically significant, and there was no significant difference in cramp intensity or how long cramps lasted. The review noted the evidence for pregnancy-related leg cramps was mixed and that more research in that group was needed.
The sleep question
Harvard Health lists insomnia among the conditions for which the evidence that magnesium could help is more limited, rather than established, without describing it as settled either way.
People taking supplements should keep to 400mg or less a day from supplements, the NHS says, because higher doses taken for a short time can cause diarrhoea. Harvard Health adds that supplements can also cause nausea and may interact with other medicines, and that it is safest to check with a doctor before starting one.
Magnesium’s established roles, in bone health, muscle and nerve function, and regulating blood sugar, remain backed by evidence even where the newer claims about cramps and sleep are not. Anyone worried about a possible deficiency, or already taking medicines, is advised to speak to a doctor before taking supplements.