Magnesium

• Movement. Muscles need magnesium for normal contraction and relaxation. A cramp is not proof of deficiency. [1] [3]
• Nerve messages. Magnesium plays a part when nerves tell muscles when to move. [1]
• Energy and bones. It helps the body use energy from food and maintain bones. More than you need does not automatically mean more energy. [1] [2]
• Migraine and sleep. Supplements may help people have fewer migraine attacks; the evidence for falling asleep faster is much weaker. Magnesium's normal role in the body does not prove either effect. [4] [5]

Wholegrain bread, oats, beans, lentils, nuts, seeds and leafy greens supply magnesium. Dairy, meat and drinking water contribute too. A varied everyday diet is a useful starting point; magnesium in food does not need restricting. [2]

The Dutch daily food guideline is 350 mg for adult men and 300 mg for adult women. The value for women stays at 300 mg during pregnancy and breastfeeding. These are not supplement doses: eating less on one day does not automatically mean you have a deficiency. Different values apply to children. [2]

Magnesium tablets probably do not noticeably prevent ordinary night cramps in older adults. Pregnancy studies disagree; suitable trials for exercise cramps were lacking. This does not test treatment of a confirmed shortage. [3]

For migraine, a review of five small studies found a possible reduction in how often attacks happen, not a way to stop an attack already underway. Use magnesium for this only under clinician supervision: amounts studied exceed ordinary supplement safety limits and can cause side effects or interact with medicines. This is not dosing advice. [4]

People also use magnesium for sleep. A small review in older adults with insomnia suggested they might fall asleep faster, but the studies were poor quality and other research was mixed. It is not a proven general sleep aid. [5]

A cramp alone does not prove a deficiency. Long-lasting diarrhoea, poor absorption, diabetes or some medicines may merit assessment. A blood test can help, but does not show all the body's stores. Discuss lasting symptoms and medicines with a clinician rather than using pills as a home test. [1] [2]

Magnesium from food is generally safe for healthy people. Supplements and magnesium-containing medicines can cause diarrhoea, nausea and stomach cramps. Dutch guidance sets 250 mg a day as the upper limit for extra magnesium from supplements; this does not include magnesium in food. [2]

With reduced kidney function, magnesium can build up. Some medicines, such as water tablets and acid-suppressing drugs, may affect magnesium levels. Ask a clinician or pharmacist about kidney disease or medicines, and do not stop prescribed treatment yourself. [1]