Guide

How important is magnesium for people who train?

Magnesium is much discussed and little demonstrated in sports nutrition. Two questions need separating: is there a risk of deficiency, and if there is no deficiency, does supplementation improve performance?

Short answer: If you are not deficient, there is no convincing evidence that magnesium supplementation improves performance. The magnesium lost in sweat is far smaller than commonly assumed. Athletes on restricted or low-calorie diets are at genuine risk of a shortfall — and there the issue is meeting intake, not enhancing performance.

Performance: what the trials show

A systematic review in healthy athletes reported that the relationship between magnesium and performance is poorly studied, with no consistent data to recommend a dose by sport.
A 2024 systematic review concluded that conclusive evidence is lacking in athletic populations, and that the optimal dose and form remain uncertain.
Another review found that current evidence does not allow a definitive conclusion: some studies report significant improvements, others do not.
An older critique of 12 experimental studies concluded that magnesium supplementation had no effect on strength or on aerobic and anaerobic performance in athletes. It is dated, but valuable as a counterpoint.

The question of sweat losses

The most common rationale is that sweating disturbs magnesium balance. A sports nutrition review corrects the scale: magnesium concentration in sweat is very low, and even in heavy sweaters the amount excreted is small. For roughly eight hours of cycling in the heat the reported total loss is around 15–20 mg.

The same review concludes that the standard ingredients of a well-balanced sports diet easily compensate for sweat magnesium losses during exercise. Some sources claim higher loss rates; those figures are not traceable to a verifiable basis.

The cramp misconception

That cramps in athletes are caused by magnesium deficiency is a widespread belief the literature does not support. The mechanism of exercise-associated cramps is considered different from cramps seen in clinical magnesium deficiency. The Cochrane review found no randomised trials at all in people who cramp during exercise — the field is empty. More in Magnesium and muscle cramps.

Who is genuinely at risk?

Athletes on restricted or low-calorie diets — common in weight-category sports.
Anyone eating a monotonous, heavily processed diet.
Those whose total energy intake stays low despite a heavy training load.

Beyond these groups, the evidence that exercise and training cause magnesium deficiency to a degree that affects health or performance is considered insufficient. Which foods are rich in magnesium is covered in Magnesium intake and deficiency.

Authorised claims

That magnesium contributes to normal energy-yielding metabolism, to normal muscle function and to the reduction of tiredness and fatigue are authorised claims. These concern normal function; a claim such as “improves performance” is not authorised and may not be used.

Practical notes

Malate and citrate are the forms usually chosen for daytime use; bisglycinate and taurate are better tolerated in the evening.
A high dose of magnesium before training is not a good idea, given its laxative effect.
Treating a supplement as something that closes a dietary gap, rather than as a performance tool, is the more accurate framing.

Frequently asked

The questions most often searched on this topic, answered as they are.

Do athletes need more magnesium?

The amount lost in sweat is smaller than assumed: for roughly eight hours of cycling in the heat the reported total loss is around 15–20 mg, an amount a balanced sports diet covers comfortably. Evidence that training causes deficiency to a degree affecting health or performance is considered insufficient.

Does magnesium improve performance?

If you are not deficient, there is no convincing evidence that it does. Systematic reviews cannot reach a firm conclusion, and an older critical review found no effect on strength or on aerobic and anaerobic performance. “Improves performance” is not an authorised claim.

Before or after training?

A high dose before training is not a good idea given the laxative effect. Malate and citrate are usually chosen for the day, bisglycinate and taurate for the evening.

Which athletes are at risk of deficiency?

Those on restricted or low-calorie diets — common in weight-category sports — those eating a monotonous, heavily processed diet, and those whose total energy intake stays low despite heavy training. The issue there is a dietary gap, not performance.

If I cramp, am I low on magnesium?

The literature does not support that assumption. Exercise-associated cramps are considered to have a different mechanism from cramps in clinical deficiency. See Magnesium and muscle cramps.