Magnesium for Athletes: What the Evidence Shows
Magnesium is involved in more than 300 enzyme reactions, from energy production to muscle contraction. Athletes are often told they need more of it, and supplements promise better performance, fewer cramps and deeper sleep. Our editorial team reviews what research supports, who is most likely to benefit and how to supplement sensibly within UK guidance.
Why magnesium matters for performance
Magnesium is essential for the production and use of ATP, the cell’s energy currency. It also stabilises cell membranes, supports nerve transmission and helps regulate muscle contraction and relaxation by interacting with calcium.
Nielsen and Lukaski reviewed the relationship between magnesium and exercise and concluded that even marginal deficiency can impair exercise performance and amplify the negative effects of strenuous activity, such as oxidative stress.
In a controlled study, Lukaski and Nielsen found that dietary magnesium depletion in postmenopausal women increased heart rate and oxygen consumption during submaximal exercise, suggesting reduced efficiency.
Athletes may have higher requirements because of losses in sweat and urine during heavy training. Combined with restrictive diets, this can push intake below needs.
How much do athletes need?
In the UK, the Reference Nutrient Intake for adults is 300 mg per day for men and 270 mg per day for women. There is no separate official figure for athletes, although some sports nutrition experts suggest needs may be modestly higher in heavy training.
| Group | UK reference intake | Practical notes |
|---|---|---|
| Adult men | 300 mg/day | Many meet this through a varied diet |
| Adult women | 270 mg/day | Lower intakes common with dieting |
| Supplement upper guidance | NHS: 400 mg/day or less from supplements | Higher doses often cause diarrhoea |
| Athletes in heavy training | No separate UK value | Focus on food first; test if symptoms suggest deficiency |
Assessing magnesium status is difficult. Serum magnesium represents only a tiny fraction of the body’s stores, so a normal blood test does not exclude low tissue levels. Doctors use it alongside symptoms and dietary history.
Signs of deficiency can include muscle cramps, twitching, fatigue, weakness and, in more severe cases, heart rhythm disturbances. These symptoms are non-specific and warrant medical assessment rather than self-diagnosis.
Some medicines, such as long-term proton pump inhibitors and certain diuretics, can lower magnesium levels, which is relevant for athletes who use them.
What the research shows
Zhang and colleagues reviewed whether magnesium supplementation can enhance exercise performance. They found that benefits were most consistent in people with low magnesium status, while results in those with adequate intake were mixed.
For muscle cramps, a Cochrane review by Garrison and colleagues concluded that magnesium is unlikely to provide clinically meaningful cramp prophylaxis in older adults with idiopathic cramps. Evidence for exercise-associated cramps in athletes is limited, and cramps likely have multiple causes, including neuromuscular fatigue.
For sleep, small trials in older adults suggest magnesium may improve some measures of sleep quality, but robust data in athletes are lacking.
Volpe has discussed magnesium in athletes and emphasised that ensuring adequate intake is important, while noting that supplementation above needs has not been shown to boost performance consistently.
Forms of magnesium supplements
Magnesium supplements come in many forms, which differ in elemental magnesium content, absorption and digestive tolerance.
- Magnesium citrate: well absorbed and widely available; can have a laxative effect at higher doses.
- Magnesium glycinate (bisglycinate): often better tolerated by the gut.
- Magnesium oxide: high elemental content but lower absorption; commonly causes loose stools.
- Magnesium malate, lactate and others: reasonable alternatives with varying research support.
- Topical magnesium (oils, flakes): little evidence of meaningful absorption through the skin.
When comparing products, check the elemental magnesium per serving rather than the weight of the compound. A tablet labelled as containing a large amount of magnesium citrate may supply far less elemental magnesium.
Taking magnesium with food may improve tolerance. Splitting doses can also reduce digestive side effects.
Magnesium can reduce absorption of some medicines, including tetracycline and quinolone antibiotics, bisphosphonates and levothyroxine, so separate them by several hours and seek pharmacist advice.
Food first, supplements second
Many foods are good sources of magnesium, and a varied diet often meets requirements.
- Pumpkin, sunflower and chia seeds.
- Nuts such as almonds, cashews and Brazil nuts.
- Wholegrains, including oats and wholemeal bread.
- Leafy green vegetables such as spinach.
- Beans, lentils and chickpeas.
- Dark chocolate with a high cocoa content.
Athletes who restrict energy, avoid entire food groups or rely heavily on refined foods are more likely to fall short. Improving diet quality should be the first step.
If supplementation is chosen, doses within UK guidance — 400 mg or less per day from supplements — are appropriate for most adults. People with kidney disease should not take magnesium supplements without medical advice, as impaired excretion can lead to dangerously high levels.
Tested athletes should opt for batch-tested products, for example those certified by Informed Sport, to reduce the risk of contamination.
Conclusions of the editorial team
Magnesium is essential for energy production and muscle function, and deficiency can impair performance.
Supplementation helps most in people with low magnesium status; evidence for performance gains in those already meeting their needs is inconsistent, and evidence for cramp prevention is weak.
Prioritise magnesium-rich foods, choose well-tolerated forms if supplementing, and stay within UK guidance unless advised otherwise by a doctor.
You may also find our articles on ZMA, on 5-HTP and sleep, and on glutamine forms helpful.
References
- Nielsen FH, Lukaski HC. Update on the relationship between magnesium and exercise. Magnes Res. 2006;19(3):180–189.
- Lukaski HC, Nielsen FH. Dietary magnesium depletion affects metabolic responses during submaximal exercise in postmenopausal women. J Nutr. 2002;132(5):930–935.
- Zhang Y, Xun P, Wang R, Mao L, He K. Can magnesium enhance exercise performance? Nutrients. 2017;9(9):946.
- Garrison SR, Korownyk CS, Kolber MR, et al. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev. 2020;9(9):CD009402.
- Volpe SL. Magnesium and the athlete. Curr Sports Med Rep. 2015;14(4):279–283.
