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Magnesium is claimed as a cure for cramp but there's little evidence to prove it

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QUESTIONI often get leg cramps and a friend suggested I try magnesium supplements to stop them. Is there any evidence magnesium helps with cramps?

ANSWER: Suddenly waking to the fiendish cramping of a calf muscle – it’s a living nightmare for many people. Cramps are sudden, involuntary contractions of one or more muscles that can cause severe pain. It’s estimated around 60% of adults experience leg cramps.

Indeed, most muscle cramps occur in the legs, particularly the calves, and usually disappear by themselves. But about 20% of people who have leg cramps have symptoms every day that are so severe they require medical intervention.

Magnesium supplements are often touted as a way to prevent leg cramps. They certainly seem to have a good biological rationale, because magnesium plays a role in regulating muscle contractions.

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In muscles, calcium binds to certain proteins, thus changing their shape and generating contractions. Magnesium acts as a natural blocker for calcium, competing for the same binding spots on those proteins and thus helping the muscles to relax.

There’s a theory that if our body doesn’t have enough magnesium to compete with calcium, this might cause the muscles to contract too much, setting off cramps and spasms. So it’s not surprising that magnesium is now routinely marketed as a solution for cramps.

However, the science really doesn’t back up this recommendation. A 2012 study by the independent British medical review group Cochrane investigated evidence on the use of magnesium supplements to prevent cramps in older adults and pregnant women.

The researchers found just four high-quality studies relating to older adults; these collectively suggested magnesium was “unlikely to provide a meaningful benefit in reducing the frequency or severity of cramps in that population”.

They also found conflicting evidence among pregnant women: one study showed a benefit in reducing cramp frequency and pain, but two others found no benefit.

A more recent review by the Cochrane group, published in 2015, looked at a variety of treatments for leg cramps in pregnancy. The researchers reviewed four trials of oral magnesium and again found that it “did not consistently reduce the frequency of leg cramps compared with placebo or no treatment”.

Muscle cramps are most likely caused by the overuse of a muscle, dehydration, muscle strain or simply holding a position for a prolonged period.

Cramps among athletes are very common. It’s thought this is because they can’t store enough water for exercise and often don’t ingest enough to replace the quantity they lose during their exertions, leading to fluid and electrolyte depletion that results in the sensitisation of certain nerve terminals.

Support for this theory about a dehydration-electrolyte imbalance comes from a number of observations, including that miners are more likely to develop cramps while working in hot and humid conditions, because of their sweat losses, and that among athletes, most cramping occurs in hot months, when the risk of heat illness is high or extreme.

A 2010 research paper in the journal Sports Health also posited that exercise-associated muscle cramp is a warning sign of a dehydration/electrolyte imbalance.

For some of us, too, night-time cramps may be caused by dehydration. But simply drinking a glass of water before bedtime isn’t going to fix the problem. We must hydrate ourselves properly throughout the day, even if that means the annoyance of multiple trips to the toilet. Also, issues such as sleep apnoea and snoring can cause greater fluid losses, as can sleeping in an overly dry or too-warm bedroom.

It’s possible, then, that the glass of water drunk with a magnesium supplement is of more benefit than the supplement itself.

Still, although current evidence doesn’t support the use of magnesium supplements to prevent cramps, you may wish to give them a try. Be aware that they interact with certain medicines, so check with your doctor first. And discuss with him or her your options if leg cramps continue to be a problem.

This article was first published in the January 19, 2019 issue of the New Zealand Listener.