Magnesium supplements: necessary or not?

2019-06-25 by Peter Hespel & Martijn Redegeld

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Anyone searching on the internet for a magnesium supplement will encounter a wide range of claims. This includes that athletes consuming extra magnesium will improve muscle contraction, optimise the energy metabolism, improve fluid status, reduce tiredness and counter muscle cramps. You might believe that it is an absolute ‘must have’ for every athlete. Or, is it all just marketing without scientific proof?

Magnesium is a mineral involved in many bodily processes. For example, it is an important element needed for a healthy skeleton, it is involved in every muscle contraction, and it is needed for the nervous system to function properly. The recommended daily dose of this mineral to prevent a potential deficiency is 250 to 300 mg. Examples of products that are rich in magnesium include nuts, vegetables, legumes and wholegrain products. If more magnesium is consumed that is needed by the body, it is not absorbed by the small intestine.

Magnesium deficiency can cause muscle cramp?

Intensive endurance exertions, and most certainly when it is hot, cause many athletes to experience painful muscle cramps. These are sudden and involuntary muscle contractions. Although the precise causes of exertion-related cramp are not clear to this day, there are different theories about how these arise. Magnesium plays a key role in one of these theories. Given the role that this mineral plays in the contraction of muscles, the idea quickly arose that the mineral could also prevent cramps during exercise. Although a variety of scientific studies have been carried out, there is still no evidence to support this theory. Magnesium supplements might only help prevent muscle cramps when there is an obvious magnesium deficiency due to an improper diet. A simple blood sample is sufficient to demonstrate whether there is a magnesium deficiency. If there is no deficiency, then it is pointless to take magnesium supplements to prevent muscle cramps. If there is a deficiency, first adjust your diet and eat magnesium-rich food more frequently.


Sweat losses

Magnesium is one of the salts lost when sweating. As sweating increases during exercise, it is often recommended that the lost magnesium is best topped up by consuming a supplement. However, this claim is not supported by scientific findings. In fact, research shows that only a very small amount of magnesium is lost when sweating. In fact, only 15 to 18 milligrams per day (i.e. 4-5% of the daily requirement) was lost during a study where participants were required to cycle for 8 hours at a temperature of 37?C! Moreover, the main amount of salt lost (±80-85%) during sweating is primarily sodium and not magnesium. So, when topping up on salt and minerals lost due to sweating, the focus is on ingesting sodium and absolutely not magnesium. By the way, a half banana after exercise is usually more than sufficient to quickly and efficiently top up on magnesium. Thus, in this case, a supplement is completely worthless.

Athletic performance

In addition to the above-mentioned claims, a lot of scientific research has been carried out on the effect of magnesium supplements on all kinds of athletic performance. Such supplements have no effect on athletes who have a proper magnesium status, nor on explosive or bursts of all-out exertions, nor on endurance performance. The VO2max or the maximum strength is also not stimulated by magnesium supplements.


Although intensive exertion can increase the need for magnesium by 10 to 20%, a magnesium deficiency rarely occurs in athletes. The increased need that arises due to heavy excretion of sweat or urine is actually compensated by the athlete’s increased consumption of food. Currently, there is insufficient evidence to use magnesium supplements as a preventative measure. Only when someone has a demonstrable magnesium deficiency can they benefit from a magnesium supplement. The most significant risk group are those recreational or professional athletes that deliberately reduce their food intake in order to lose weight. A calorie-poor diet reduces the total consumption of food, which automatically reduces the consumption of magnesium. This also applies to other important minerals and micronutrients, such as iron and vitamins. A blood test will reveal if there are any deficiencies, and, if necessary, it should be followed up on via a supplement prescription personalised to the individual.