Foto: Canva.com/Jan-Otto

Magnesium – alongside iron – is one of the most commonly used minerals in sports supplements and is primarily taken as a preventive measure against muscle cramps.

But is magnesium really as helpful in preventing and treating cramps as is often claimed? Magnesium is certainly essential for the proper functioning of our entire metabolism – especially for normal muscle and nerve function and for supporting the immune system. However, many other nutrients are just as necessary as magnesium.

The reason for the Swiss “magnesium myth” lies not only in clever marketing but also in a case report over 30 years old about a tennis player whose cramps disappeared after a long match thanks to a high dose of magnesium. Numerous other studies, however, have shown that magnesium is only likely to be effective if there is an acute magnesium deficiency – something that is very rare in practice.

Absorption of magnesium

The best and most effective source of magnesium is a balanced diet. Foods particularly rich in magnesium include nuts, leafy green vegetables (especially spinach), legumes such as beans, fish, whole grains, avocados, bananas, and dried fruits.

Only when there is a confirmed magnesium deficiency (which can easily be diagnosed by a specialist) does supplementation make sense. It is important to choose the right form of magnesium, as not all supplements are equally well absorbed by the body. There are various magnesium compounds that mainly differ in their bioavailability – that is, how well the body can absorb and utilize them. Magnesium citrate and magnesium bisglycinate are particularly well absorbed.

Some forms are also better suited to specific times of day: magnesium bisglycinate is often taken in the evening because it has a calming effect and can promote sleep. Citrate, on the other hand, is better suited for daytime use, as it can help reduce stress.

Too much magnesium is possible

There is also evidence that high magnesium intake from supplements can cause unwanted side effects such as diarrhea or inhibit the absorption of iron or zinc. Accordingly, the so-called tolerable upper intake level – the amount that should not be exceeded over the long term – is set very low for magnesium. In Switzerland, it is only 250 mg per day, which is actually lower than the recommended daily intake of about 300 to 400 mg. However, this limit applies only to magnesium from supplements or fortified foods (e.g., functional food), not to magnesium from natural foods.

Salt loss as a “cramp trigger”

A much more common cause of cramps is salt loss due to physical activity. A study of American football players found that those prone to muscle cramps lost more sodium through sweat during training than their teammates without cramps. The affected players also had a greater imbalance in sodium levels, which can further increase the risk of cramps.

A study by Edith Cowan University (2021) confirmed that drinking sodium-containing electrolyte drinks during and after exercise reduced the likelihood of muscle cramps compared to drinking plain water. This supports the theory that a deficiency in electrolytes – especially sodium – contributes to the development of cramps, and not dehydration alone. In endurance sports, sodium supplementation has proven useful during prolonged efforts – most easily through salt tablets or added salt in sports drinks.

Often other causes of muscle cramps

Often in sports, cramps are actually caused by changes in muscle load or simply muscle overexertion. In a triathlon, for example, cramps can occur both after the transition from the horizontal swimming position to the bike and then again when switching to running, because the type of effort changes completely within seconds and the muscles first need to adapt to it again.

When a muscle cramps, it is simply overwhelmed by the current demand. In sports, this usually occurs when, for example, you are moving faster than usual in a competition and the muscle is not accustomed to this intensity. Or when the muscle is exposed to an explosive effort for which it has not been gradually prepared through training.

Cramps also often do not occur right at the start of an activity (except in the case of explosive or completely unfamiliar movements), but only when energy reserves are depleted and the muscle is fatigued. Possible causes include inadequate or poorly targeted training – or simply the duration of the effort exceeding what the body is used to.