Can magnesium reduce leg cramps?


In this episode, we explore pesky muscle cramping in sports. There are so many  treatment methods athletes use to avoid and treat cramping, but how do you know they work?

There are so many internet sites selling magnesium supplements and topical magnesium sprays to treat cramping. Find out if it’s worth spending your hard earned dollars. As always don’t forget to head over to iTunes and rate with show when you get a chance or leave a comment below.
Check out this episode!

Does magnesium reduce leg cramps?

Podcast Summary

2.21 Magnesium is an essential mineral involved in many chemical processes in the body. It helps to produce energy and it’s important for cell function. It keeps heart rhythm normal and supports nerve conduction. It does all these amazing things, but the question is can it do more?

3.01 Muscle cramping is very common in sports. If you talk to athletes regularly, or are an athlete yourself, you would know cramping is one of the most annoying and painful things to experience during training or racing.

3.19 Runners, swimmers, cyclists, triathletes, footballers, netballers, walkers and dancers all complain about getting muscle cramps. You can get cramps during training, racing, after training, during the night whilst you’re asleep or sitting in a chair. In other words, muscle cramps can debilitate you anytime, anywhere.

3.40 It’s common belief that magnesium supplementation is the key to treating muscle cramps, but is it another urban legend?

How much magnesium do you need per day, is everyone deficient?

3.58 Magnesium deficiency is very difficult to measure. This is because magnesium doesn’t just float around in the blood. Serum magnesium (the amount found in blood) only account for 1% of our magnesium store. This means when you take a blood sample to measure magnesium, you’re not really measuring magnesium levels at all. [1] Over half of our magnesium stores are found in bone. Source.

4.57 In the medical sense there is such a thing as magnesium deficiency. This is usually caused by a person having low magnesium intake usually due to: malnutrition, prolonged diarrhea or excessive urinary loss. Magnesium deficiency in the medical sense is very rare.

6.19 It’s common belief at the moment, at least amongst personal trainers and naturopaths that people are magnesium deficient population wide, this has never been measured and it’s highly unlikely because it’s found in so many foods.

How much magnesium should I be aiming for?

6.50 The recommended daily intake for magnesium for adult males is 420mg per day, and for female’s 320mg per day. Source.

Where do you get magnesium from?

6.56 Magnesium is a common mineral found in the diet and in the body. It is stored in muscles and soft tissue. It plays a role during muscle contraction.

7.06 Magnesium is found in a wide variety of foods including plants and animals. Most green vegetables, legumes, beans, nuts, shellfish and spices are magnesium rich. You can also find moderate amounts of magnesium in unprocessed grains and cereals, tubers, fruit and oils. Source.

7.25 Here is a list of foods with their magnesium content, just to give you and idea of how easy it is to get enough magnesium in your diet. Table Source.


Food Serve size Magnesium in mg
Spinach ½ cup 83
Potato with skin 1 medium 52
All bran cereal 30g 111
Quinoa cooked ½ cup 47
Brazil nuts ¼ cup 133
Lentils cooked ¾ cup 52
Peanut butter 2 tbsp 52
Salmon 75g 92
Sesame seeds 30ml 68


The claim that “most people are deficient”, doesn’t make any sense to me. For starters how do you know people are deficient if you can’t measure it? And how can people be deficient if magnesium is found in a variety of food? This is especially true if someone is eating a healthy diet, which you would assume if you’re into training you would be conscious of what you eat.

How is magnesium absorption affected?

9.07 There are a few things that affect absorption of magnesium in the diet. A high fibre diets between 40-50g daily have lower absorption rates of magnesium. Protein is also a contributing factor, too little protein (<30g per day) decreases absorption or too much (>94g per day) causes greater renal excretion of magnesium. Source.

10.11 The kidneys regulate the amount of magnesium we hold on to in the body and the careful balance the body needs to function properly.

Does supplementation for cramping work?

10.26 It has long been thought that magnesium supplementation is the solution for all sorts of muscle cramps, but the evidence on magnesium does not show this.

What are muscle cramps?

10.42 Cramps are sudden muscle spasms that feel like your muscles have stiffened tightly. It’s uncomfortable and some times very painful. I often have friends at training complain of cramping in their feet or calves during swimming training. I’ve also had elderly clients complain of lower leg muscle cramps at night, and even pregnant women. Cramps can happen to anyone, anywhere, at any age.

11.23 No one knows why cramps occur at odd times, like when you’re asleep or always in swimming in the pool, but they do. Cramps are more likely to occur if the muscle if tired or untrained.

The theory; how are muscle cramps caused?

11.48 There are many theories, about how cramps are caused, but no one really knows the answer. Common reasons you will hear is that they are due to changing your exercise movement patterns. For example if you are a cyclist and you recently changed your bike seat height.

12.43 There is also thought that there is a genetic component to cramping. Some people cramp more than others, for no apparent reason at all.

12.58 In a 2005 study, researchers looked at college-aged men and how different supplementation can affect the rate of cramping. They took 13 men and made them exercise doing calve exercises to fatigue. They initially took the group into a trial that involved consuming carbohydrates with electrolytes (sodium chloride), in a hot environment 37 degrees with 60% humidity. Then they measured the rate of cramping.

13.28 Then in a second trial they repeated the scenario this time were not allowed to consume any fluids. The results were when participants consumed the carb and sodium beverage they cramped less. This allowed the men to exercise for longer.

13.45 However, they do not believe that hydration is the only treatment or cause of cramping. The carb and sodium group still cramped in 69% of the people. And of course the dehydration group, where they had no fluid, cramped the most. [2]

14.25 Scientists think the most probable cause of cramps is due to an acute loss of fluid caused by medication that induces dehydration. In the case of sports, they believe it’s caused by dehydration from sweating (perspiration) as you exercise and electrolyte shifts.[1]

Some researchers believe very strongly that magnesium, potassium and calcium deficiency can also cause cramps. But research in this area is very mixed and some studies very poorly designed its difficult to draw any conclusions from it.

15.06 Potassium depletion can also be an issue amongst the elderly, especially if taking diuretics. Hypokalemia can also cause muscle cramps. [3]

15.24 Whilst depletion in mg, K+, Ca+ might be a contributing factor cramps for cramps in the elderly or deficient people, in athletes this has not been the case. Athletes are typically well fed so it’s unlikely they have a deficiency and very little mg, K+ and ca+ is lost during exercise.

15.48 In summary, cramping could be caused by genetics, dehydration, lack of minerals, electrolyte shifts, heat and fatigue.

What happens when you supplement Magnesium?

16.05 The way we can test if supplements work is if we test two groups. Researchers in Argentina looked at people that cramped regularly. So they needed to have cramped at least 6 times in the last month. There were 45 subjects in total, and they were randomised in two groups. One group was given 900mg of magnesium citrate twice daily (1800mg daily) and the other group a sugar pill, a placebo.

16.46 They took the pills for a month and recorded the number of cramps they had. Both groups had a wash out period of 1 month, where they both took nothing. Then they swapped. The placebo group got the magnesium, and the magnesium group got the sugar pill.

17.16 The results were not impressive, but conclusive. There was no difference between the magnesium or placebo groups in the number and intensity of cramps they had.

17.21 Both groups (placebo and mg group) did report less cramping during the time, but this indicates there is bias, in other words the placebo effect at work.

18.02 People associate magnesium supplementation with the reduction of cramps so they believed it worked. But because both groups reported the same amount of cramping, the conclusion can be drawn that it’s not the magnesium that caused the reduction in cramps, but the belief they were taking something that could reduce cramps with. [4]

Topical magnesium sprays for cramping during exercise do they work?

18.42 Topical magnesium sprays are commonly used by athletes to reduce cramping. Companies that make these types of products used magnesium salts that also contain other trace minerals this is then put into oil based solution and sprayed on to the affected area.

Lots of people of my Facebook page said they used this type of product for sports, and wanted to know; do they work?

The physiology and chemistry behind skin absorption

19.15 The skin is designed to be a protective barrier to infection, metal poisoning and a wide range of nasty substances we naturally find in our environment.

The skin has several layers of epidermis, which is just soft tissue. On the skin surface we have glands and hair follicles, which make up only 1% of the total skin surface area.

19.50 Chemicals can be rapidly absorbed through the glands and hair follicles, but because this is only a small part of skin, if anything is going to absorb through it will be through the epidermis.

20.00 Certain chemicals can diffuse through the layers of epidermis and then dermis and reach the lymph system, but this process is really depends on the chemical stability or instability of the chemical trying to pass through.

20.35 To explain this we have to pass back in time to chemistry class. Magnesium chloride is an ionic substance. This means the magnesium metal has charged particles or ions. Positive ions are metals that have lost one or more electrons, whereas negative ions are formed by non-metals that have gained electrons.

20.56 Ionic substances do not pass through the skin easily, therefore topical sprays containing ionic substance like magnesium will not get through the skin. The only way to drive ions through the skin is by using an electric current. This is called iontophoresis. A magnesium spray will not do this.

21.40 If we look at other known poisonous metals the story is a little different. I should add a caveat here most metals including magnesium and iron can be toxic to humans at high enough doses. So just because magnesium is essential for the human body to function, having too much magnesium in the body can also be poisonous and lead to health problems.

22.50 Lets look at how other metals, like heavy metals are able to pass through the skin. Heavy metals are metals with a density >5.0. They are technically semi-metals.

23.08 Heavy metal poisoning from absorption from the skin is rare. It’s because this type of absorption is very slow and can only be done with certain heavy metals such as zinc, copper, chromium, iron and manganese, lead, mercury, arsenic.

23.33 Typically these metals are absorbed into the body contaminated on food, in the air vaporised or ingested. Say for example you have touched one of these metals with your hands and placed your fingers to your mouth or rubbed your eyes.

24.14 Absorption of substances across skin is dependent on many factors;

  • The surface area of the skin exposed
  • The duration of exposure
  • The concentration of the chemical
  • The permeability coefficient of the chemical (how easily does it get through the skin)
  • The weight of the person
  • The nature of the exposure ie topical spray? or bathing in it?

24.58 Simple things like washing chemicals or metals off the skin can get rid of a lot of exposure and hence reduce absorption. If you are talking about a magnesium topical spray used before exercise it will wash off with sweat and won’t get absorbed.

25.25 There is an unpublished study on the internet which is an experiment that is quoted in every woo website. The experiment went something like this; 19 subjects in the UK were recruited to take baths daily in a solution of magnesium and water at temperature of 50-55degrees. They bathed daily for 12minutes and there was full body exposure.

25.40 After bathing for 7 days straight 17 people out of the 19 showed increased magnesium concentration in blood samples. This study is used to prove magnesium can be absorbed through the skin. Source.

25.53 I have a few problems with this study. Firstly it’s not peer reviewed and was never published in a scientific journal, which means anyone could have written this and published it on the internet.

26.03 Secondly bathing in any solution obviously increases exposure (skin surface area) as well as exposing other openings to the body. Lets face it most drugs are more rapidly absorbed when taken anally. There’s glands, and access to the digestive system that’s makes absorption more rapid than taking things orally.

26.43 Lastly, this experiment doesn’t prove topical magnesium sprays work. You don’t bathe in topical sprays and you don’t have nearly enough surface area of the skin exposed. We aren’t even certain magnesium helps with cramps anyway. The whole thing is complete non-sense.

How to I treat a muscle cramp?

27.10 Stop exercising! Try to lengthen or stretch out the muscle. Basically you are trying to relax the muscle. Sometimes massaging the muscle belly helps. Usually doing this for a few minutes is enough and you can continue on exercising, slowly.

27.30 If the cramp is very painful or bad, then applying ice might help as well. Typically if you have cramped in the one spot at that particular training session, if you continue to train hard, the area will cramp again. Ease back into exercise slowly.

27.58 How do you stop cramping during exercise?

  • Genetic component, you can’t choose your parents!
  • Make sure you are well hydrated
  • Have enough rest between training sessions to allow your muscles to recover
  • Try not to increase intensity at the end of your training session
  • Use a progressive exercise program

28.30 Keep in mind that if you have previously cramped, you are more likely to cramp more often. Cramping is also more common in endurance athletes, intensity and duration of exercise is very important. The more intense you exercise the higher the risk of cramping. In addition, the temperature in which you exercise, hot or humid, is the worst thing for cramping. [5]


29.01 At the moment the research is inconclusive in the effectiveness of magnesium supplementation for cramps. Some times the belief that something will work is worthwhile. Magnesium will not harm you if you take it in the recommended dose, but it will not benefit you in regards to cramping.

  1. Nguyen V. Magnesium supplementation in the reduction of muscle cramps: A systematic literature review. The Australia Journal of Pharmacy 2013. 94.
  2. Dale A et al. Influence of Hydration and Electrolyte Supplementation on Incidence and Time to Onset of Exercise-Associated Muscle Cramps. Journal of Athletic Training, 2005. 40: p. 71-75.
  3. Gaby R, Nutritional Interventions for Muscle Cramps. Integrative Medicine, 2007. 6.
  4. Frusso R, et al.Magnesium for the treatment of nocturnal leg cramps: a crossover randomised trial. Journal of Family Practice, 1999. 48(11): p. 868-71.
  5. Schwellnus M.P, N.Drew, and M.Collins, Muscle cramping in athletes–risk factors, clinical assessment, and management. Clinical Sports Med, 2008. 27(1): p. 183-94, ix-x.

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