Magnesium for cramps: which type works and how much to take

It’s three in the morning and your calf goes hard as a rock. You jump out of bed, plant your foot on the cold floor, and wait for it to ease up. The next day, someone tells you the same old thing: it’s a magnesium deficiency. So you buy a bottle.

We’ll tell you plainly, even though we sell magnesium. For most cramps, magnesium isn’t the solution, and the most rigorous studies make that pretty clear. In this article, we’ll tell you what the trials say about each type of cramp, what really causes them, what to do when one strikes, how to prevent them, and when it does make sense to take magnesium, which kind, and how much.

Garrison SR et al., Cochrane Database of Systematic Reviews, 2020, review “Magnesium for skeletal muscle cramps” with 11 randomized trials and 735 participants. The certainty of the evidence follows the GRADE system used by Cochrane.

Does magnesium help with cramps? What the trials say

The question has a pretty good answer, which is rare in the world of supplements. In 2020, the Cochrane Collaboration updated its review on magnesium and muscle cramps. They brought together all the randomized trials they could find, eleven in total, and separated them by type of cramp, which is the right thing to do because not all cramps are the same.

The most studied group is people with nocturnal leg cramps with no apparent cause, which doctors call idiopathic, with an average age of 62 to 69. This is the most common type of cramp. The results are clear: magnesium reduced cramps by 0.18 per week compared with placebo, such a small difference that it was not statistically significant. The percentage of people whose cramps improved by at least 25% was virtually identical in both groups, and the evidence for this outcome is rated high certainty.

The authors’ exact conclusion is that magnesium is unlikely to provide clinically meaningful prevention of cramps in older adults.

The trial that explains why so many people swear it works

In 2017, an Israeli team published a trial in JAMA Internal Medicine involving 94 people with an average age of 65 who had at least four nighttime cramps every two weeks. Half took magnesium oxide every night for four weeks, and the other half took an identical placebo. The dose was no small amount: 520 mg of magnesium per day, twice the recommended limit for supplements.

And here’s the interesting part. Both groups improved. Those who took magnesium went from 7.8 to 4.4 cramps per week. Those who took the sugar pill went from 8.5 to 5.5. The difference between the two was 0.38 cramps per week, essentially nothing. The authors themselves put it plainly: the improvement in both groups is probably a placebo effect, and that may explain why magnesium is used so much for cramps.

Pregnancy, the only area with some evidence in its favor

The picture is less clear in pregnancy. A 2015 Thai trial involving 86 pregnant women between 14 and 34 weeks found that 300 mg of magnesium bisglycinate daily for four weeks halved cramps for 86% of participants, compared with 60.5% in the placebo group. But other trials found no differences, and the Cochrane review specifically on cramps during pregnancy, covering eight studies and 576 women, rates the evidence as low or very low and does not go so far as to conclude that any intervention works. We’ll take a closer look below.

And in sports, not a single trial

This surprises many people. The review found no trial testing magnesium for exercise-associated cramps, the very kind most heavily advertised in sports supplement stores. It’s not that it’s been proven not to work. It’s that nobody has properly checked.

Why cramps happen (and why it’s almost never a magnesium deficiency)

A cramp is an involuntary, sudden, painful contraction of a muscle or part of one. It feels hard to the touch and usually lasts from a few seconds to several minutes. It’s very common. According to a review in American Family Physician, up to 60% of adults have had nighttime leg cramps at some point, and they’re more common with age.

The idea that every cramp is a mineral problem comes largely from medical records of industrial workers who sweated liters in very hot environments, as a 2019 review in Sports Medicine points out. In those cases, there really were huge losses of water and salt. But most of the cramps you get aren’t like that.

Exercise cramps have more to do with fatigue than minerals

The study that most changed this understanding was conducted with 210 Ironman triathletes. They had their blood drawn and were weighed before and after the race. Forty-three had cramps. When researchers compared those who did and didn’t, there was no difference in their blood electrolytes or weight lost through dehydration. What set the athletes who had cramps apart was that they had gone faster than planned and had had cramps in previous races.

The explanation best supported today is neuromuscular. When a muscle becomes fatigued, especially when it is working in a shortened position, the signals from the spinal cord telling it when to contract and when to relax become unbalanced, and the contraction starts on its own. That 2019 review takes this a step further. There are probably several types of cramps with different mechanisms, some linked to water and salt loss and others to fatigue, which is why there’s no single remedy that works for everyone.

What causes nighttime cramps

In most cases, no specific cause is found. But there are factors that make them more likely, and it’s worth knowing about them.

• Age. They become more common after 60.
• Pregnancy, especially in the third trimester.
• Some medications. A study using data from 4.2 million people in British Columbia, Canada, found that treatment for cramps was 2.4 times more likely in the year after starting a long-acting inhaled bronchodilator, 2.1 times more likely with potassium-sparing diuretics, and 1.5 times more likely with thiazide-type diuretics. The association with statins was small. This was an observational study of people over 50, so it shows an association, not causation, but it offers a useful clue.
• Conditions such as kidney failure and dialysis, cirrhosis, diabetes with neuropathy, hypothyroidism, lumbar spinal stenosis, or poor venous circulation.
• Summer. The same Canadian group found that prescriptions for cramps and online searches for “leg cramps” almost double between winter and the height of summer. No one knows why yet.

How to get rid of a cramp right away

The answer here is simple and well supported. Gently stretch the muscle that has contracted and hold the stretch until it relaxes. This is what both a 2022 review by the American association of athletic trainers on cramps in athletes and health information from the U.S. National Library of Medicine recommend.

• Calf. With your leg straight, pull the tip of your foot toward you with your hand or a towel. If you’re standing, keep your heel on the floor and lean your body forward. Once the cramp eases, take a few steps on your heels.
• Sole of the foot and toes. Pull your toes upward with your hand and massage the arch.
• Hamstrings, the back of the thigh. Sit with your leg straight and lean forward from the hips, without bouncing.

Afterward, a gentle massage and some local heat can help the muscle relax. If you’re still sore the next day, that’s normal. The muscle can remain tender for hours.

The curious case of pickle vinegar

There’s a locker-room remedy backed by a study that’s worth mentioning for what it teaches us. In a 2010 study, several dehydrated men were induced to have a cramp in a foot muscle using electrical stimulation. Drinking about 75 ml of pickle juice shortened the cramp by 49 seconds compared with drinking water. What’s striking is that nothing changed in their blood during those minutes. The authors think the effect is a reflex triggered in the mouth and throat by the sour taste, not a replenishment of salts.

Be careful about jumping to conclusions. These were cramps induced in a lab, not the ones you get in your calf at three in the morning. But it helps explain that cramps are often a nerve signaling problem, not a mineral deficiency.

Nighttime calf cramps: how to prevent them

They’re the most common and the most bothersome because they wake you from sleep. Here’s what has some evidence behind it.

Stretching before bed, with caveats

A 2012 Dutch trial with 80 people over the age of 55 compared stretching the calves and hamstrings every night just before bed with doing nothing. After six weeks, the stretching group had fewer cramps, and they were less intense. By contrast, a 2005 English trial with 191 patients from 28 health centers found no effect from calf stretches. The evidence is mixed, but stretching costs nothing and carries no risks, so it’s worth trying for a few weeks.

A simple example. Stand facing a wall, place your hands on it, step one leg forward, and leave the other behind with your heel on the floor and your knee straight. Hold for ten seconds, rest for five, and repeat three times with each leg.

Foot position in bed

Sleeping with your foot pointed like a ballerina leaves your calf shortened for hours, which is exactly the position in which the muscle tends to cramp. If you sleep on your stomach, let your feet hang over the edge of the mattress. If you sleep on your back, make sure the sheets don’t push your feet downward. It’s common-sense advice, not backed by its own trial, but it has no contraindications either.

Quinine and tonic water

For decades, quinine was the standard treatment for nighttime leg cramps. A Cochrane review of 23 trials found that it reduces the number of cramps by around 28%, at doses of 200 to 500 mg a day. The problem is its side effects, which are rare but can be serious, such as blood, heart rhythm, vision, or hearing disorders. In 2010, the U.S. Food and Drug Administration advised against using it for this purpose, and the American Family Physician review is categorical: it should not be used for nighttime leg cramps.

What about tonic water? It does contain quinine, but very little. The German limit cited by Germany’s Federal Institute for Risk Assessment is 85 mg per kilo in non-alcoholic drinks. That means at most about 28 mg in a 33 cl can, compared with the 166 mg of quinine base in a single dose of the kind once used for cramps. You’d have to drink several liters to feel any effect, and that same institute recommends that pregnant women avoid drinks containing quinine as a precaution.

Cramps during pregnancy: the one case where magnesium has something going for it

Leg cramps are a common discomfort during pregnancy, especially in the third trimester. And magnesium has a little more going for it here than in other cases, though less than people often say.

The 2020 Cochrane review on cramps during pregnancy included eight small studies with 576 women. The results for magnesium were inconsistent. In one trial, more women stopped having cramps altogether. In another, involving 86 pregnant Thai women, more women cut their cramps in half. But magnesium made no difference in other measurements. Since each study measured things differently, the data couldn’t be combined, and the certainty was low or very low. The review concludes that it’s unclear whether any of the options studied—magnesium, calcium, or vitamins—actually work.

One detail few people know: the European Food Safety Authority sees no reason to increase magnesium intake during pregnancy, and maintains the same guideline as for any adult woman: 300 mg a day.

You can find more details about the different stages in our article on magnesium for women.

Cramps during exercise: pace, training, and heat

A cramp at mile 22 of a marathon, in the final set of a padel match, or while climbing a hill on your bike has a very recognizable pattern. It appears in the muscles working hardest, when they’re tired, and often when you’re going faster or for longer than you’ve trained for.

What the experts who have studied this most recommend is stopping the search for a single cause. The 2022 review in the Journal of Athletic Training, co-authored by the author of the Ironman study, concludes that exercise cramps result from a mix of factors that vary from person to person, and that prevention works better when tailored to each individual than with generic advice like “drink more.”

• If you always get them at the end of races, the most likely factor is pace. Starting faster than your training justifies is a classic mistake.
• If you get them in hot weather and sweat a lot, leaving white salt marks on your clothes, it makes sense to replace water and salt during exertion.
• If you get them during an event that’s longer than usual, the answer is to train for that duration progressively, not to take a supplement.
• If you’ve had them before, you’re at greater risk, as the Ironman study found. Bear this in mind when planning your pace.

For details on what is and isn’t known about magnesium specifically for athletes, see magnesium for athletes. Sweating does cause some magnesium loss, but trials haven’t shown that this leads to fewer cramps.

If you decide to take magnesium: which type and how much

Even with all of the above, you may still want to give it a try. It’s reasonable if you suspect you don’t get enough magnesium from your diet, if your doctor has found that your levels are low, or if you’re in a situation where there’s some evidence, such as pregnancy, and always with your doctor’s approval. Here are the rules for doing it right.

Adequate intakes from the European Food Safety Authority (EFSA, 2015). The Scientific Committee on Food set a maximum level of 250 mg per day for readily dissociable magnesium salts and oxide in supplements, adopted by the EFSA, which does not include magnesium from food. Doses from the trials by Supakatisant and Phupong (2015) and Roguin Maor et al. (2017).

Two clarifications about the table. The 250 mg limit applies only to magnesium from supplements, not from food, which doesn’t cause problems in healthy people. And that diarrhea is the most common side effect is confirmed by the Cochrane review itself, where between 11% and 37% of those taking magnesium experienced digestive discomfort, compared with between 10% and 14% taking a placebo. If you want more detail on this, see magnesium side effects, and for differences between salts, see types of magnesium and what each one is used for.

Before turning to supplements, take a look at your plate. Nuts, legumes, whole grains, cocoa, and leafy green vegetables cover much of what you need, and in magnesium-rich foods we tell you all about it using real serving sizes. And if you have several symptoms at once and suspect a deficiency, in magnesium deficiency we explain when it’s worth getting a blood test.

What we can tell you about our magnesium

Magnesium Matrix combines four salts, citrate, bisglycinate, malate, and taurate, with no oxide. We’re not going to tell you it gets rid of cramps, because as you’ve seen, there’s no evidence for that, and EU regulations don’t allow it. What Regulation (EU) 432/2012 does allow us to say is that magnesium contributes to normal muscle function and that it helps reduce tiredness and fatigue.

An honest note about the dosage. The two daily tablets provide 375 mg of magnesium, above the 250 mg limit the EFSA sets for supplements. So the sensible thing is to split them into two doses, and if you notice loose stools, reduce the amount.

Magnesium Matrix

Magnesium citrate, bisglycinate, malate, and taurate, with no oxide. 375 mg of magnesium in 2 tablets, 60 tablets for 30 days. Suitable for vegans, gluten-free, and lactose-free. Magnesium contributes to normal muscle function and helps reduce tiredness and fatigue.

19,96 €

View Magnesium Matrix

When to see a doctor about cramps

The vast majority of cramps are harmless and don’t require a doctor’s visit. But there are situations where it’s a good idea to see your GP.

• They are very severe, frequent, or long-lasting, or they are becoming harder to release.
• They do not ease when you stretch the muscle.
• They regularly keep you from sleeping.
• They started after you began taking a medication or you have a chronic condition, such as kidney, liver, or thyroid problems, or diabetes.
• They are accompanied by persistent weakness, muscle loss, or tingling.

One more thing. Routine electrolyte blood tests for cramps usually do not add much, according to the American Family Physician review. Your doctor will order specific tests if your medical history or examination points to a particular cause.

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