Does magnesium help sleep and muscle cramps?

Does magnesium prevent muscle cramps?

The best evidence is the Cochrane review of magnesium for skeletal muscle cramps (updated September 2020). It included 11 trials: 5 in older adults with idiopathic cramps, 5 in pregnancy-related cramps and 1 in liver cirrhosis. For older adults, magnesium probably makes little to no difference to cramp frequency at four weeks (moderate certainty) and is unlikely to reduce cramps of moderate or worse intensity. For pregnancy, certainty is very low, so no conclusion can be drawn. None of the trials studied exercise-associated cramps.

For exercise cramps, a 2009 British Journal of Sports Medicine review concluded that the electrolyte-depletion explanation rests on weak evidence and that altered neuromuscular control (fatigue) is the better-supported cause. See do salt tablets prevent cramps. The Australian Institute of Sport places magnesium in Group C, not advocated for athletes without a clinical reason.

Does magnesium help you sleep?

Magnesium takes part in nerve and muscle function, which is why it is popular for sleep. In people who already get enough, there is no good evidence it improves sleep, and claims that glycinate is proven better than other forms outpace the evidence. Small trials, often in older adults or in people with low intake, rate as low quality. A worthwhile sleep plan starts with regular hours, caffeine timing, light exposure and treatment of sleep apnoea or pain.

When might a supplement make sense?

• Your diet is low in magnesium-rich foods (nuts, legumes, whole grains, leafy greens).
• A doctor has found a low blood magnesium or you take medication that depletes it (for example some diuretics or acid-suppressing drugs).
• You are a heavy sweater on a restricted diet.

Even then, check your food first.

What dose and form?

Typical supplements supply 100 to 350 mg elemental magnesium. The EFSA upper level for supplemental magnesium is 250 mg a day for adults. Citrate, glycinate and bisglycinate are better absorbed than oxide. In South Africa (October 2026) costs per 100 mg elemental are about R2.64 for The Real Thing Tri-Mag, R2.82 for Flora Force Magnesium Glycinate and R3.37 for Dis-Chem Gold Magnesium Chelate. See glycinate versus citrate and the best magnesium in South Africa page.

What are the risks?

• Diarrhoea is the most common side effect, especially with oxide and large citrate doses.
• Kidney disease: magnesium can accumulate; avoid unless prescribed.
• Interactions: separate from tetracycline or quinolone antibiotics and bisphosphonates by a few hours.

When should you see a doctor?

Persistent night cramps, cramps with weakness or swelling, cramps starting after a new medication, or sleep trouble lasting weeks warrant a doctor's visit. Pregnant women with leg cramps should ask their midwife or doctor before taking any supplement. Under-18s should not self-prescribe magnesium.

Related reading: how much magnesium per day.

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