Magnesium is essential for normal energy metabolism and muscle function, but most runners do not automatically need a magnesium supplement. A varied diet can usually provide enough, and the evidence does not show that taking extra magnesium reliably improves running performance or prevents exercise-associated cramps in people who are already getting enough.
Key takeaways
- UK guidance says adults aged 19–64 need 300mg of magnesium a day for men and 270mg for women.
- Spinach, nuts, seeds, beans, wholegrains and wholemeal bread can all contribute to daily intake.
- Research on magnesium and athletic performance is mixed; correcting a shortfall is different from taking extra when your intake is already adequate.
- Magnesium is widely marketed for cramps, but a Cochrane review found no randomised trials testing it for exercise-associated muscle cramps.
- RunStrong does not provide a meaningful nutritional dose of magnesium and should not be used as a magnesium supplement.
What does magnesium do?
Magnesium is a mineral involved in many processes throughout the body. The NHS highlights its role in turning food into energy and supporting normal parathyroid function, which is relevant to bone health. Magnesium is also involved in normal muscle and nerve function, which explains why it frequently appears in sports-nutrition conversations.
That biological importance does not mean that more is always better. The useful question is not simply whether magnesium matters; it is whether a runner's diet or clinical circumstances leave them short.
Do runners need more magnesium?
Training changes energy use and can increase sweat losses, so researchers have investigated whether physically active people have different magnesium requirements. A 2017 review found associations between magnesium status and several measures of muscle performance, while noting that much of the human evidence focused on physiological markers rather than direct sporting performance.
A broader 2019 systematic review of minerals and athletic performance judged the magnesium evidence stronger than that for many other minerals, but still concluded that more high-quality research was needed before routine supplementation could be supported. That is an important distinction: low magnesium status may impair normal function, but it does not follow that every runner will become faster by adding a supplement.
In practice, food intake, total energy availability, medical history and any confirmed deficiency matter more than the fact that somebody runs.
How much magnesium do UK adults need?
According to the NHS, adults aged 19–64 need:
- Men: 300mg a day
- Women: 270mg a day
The NHS says you should be able to get the magnesium you need from a varied and balanced diet. Useful food sources include spinach, nuts and wholemeal bread. Seeds, beans, lentils and other wholegrains can also make it easier to build magnesium into normal meals.
For runners, this means looking at the whole day rather than hunting for a single “recovery food”. Porridge or wholegrain toast at breakfast, beans or lentils with lunch, leafy vegetables with dinner and a small portion of nuts or seeds can contribute without creating another complicated supplement routine.
Does magnesium improve running performance?
The honest answer is: possibly when magnesium status is low, but there is no convincing case for treating it as a universal performance booster.
Some studies have reported changes in muscle-performance measures after supplementation, while others have found little practical benefit. Study populations, magnesium status, supplement doses and performance tests vary considerably. Results in people with low intake, older adults or a diagnosed deficiency cannot automatically be applied to a well-fed runner.
This is why “magnesium is essential” and “every runner should supplement magnesium” are not the same claim. The first is established physiology; the second goes beyond the evidence.
Does magnesium prevent running cramps?
Magnesium is heavily promoted for muscle cramps, but the evidence is much less certain than the marketing suggests.
A 2020 Cochrane review examined 11 trials involving 735 people. For idiopathic cramps—mainly night cramps in older adults—magnesium was unlikely to provide a clinically meaningful benefit. Crucially, the review found no randomised controlled trials evaluating magnesium for exercise-associated muscle cramps.
That does not prove magnesium can never matter. A confirmed deficiency is a different clinical situation. It does mean that getting cramp during a long run is not, by itself, evidence that you need magnesium.
Current exercise-cramp research points towards a combination of individual factors, often including neuromuscular fatigue, pace, training history and previous cramp. Our guide to running cramps explains what to do during a cramp and how to build a more useful prevention plan.
Food first or supplement?
Food first is the sensible default because magnesium-rich foods bring protein, carbohydrate, fibre and other micronutrients with them. A supplement may be worth discussing with a GP, pharmacist or registered sports dietitian when:
- your diet is highly restricted or consistently low in magnesium-rich foods;
- a clinician has identified a deficiency or a medical reason for supplementation;
- you have a condition, medicine or gastrointestinal issue that may affect nutrient status; or
- you have persistent symptoms that need proper assessment rather than guesswork.
Fatigue, poor sleep, twitching and cramps are non-specific. They can have many causes, including training load, low energy availability, iron problems, medicines and underlying health conditions. They should not be used as a DIY magnesium test.
RunStrong's blood-tests guide for UK runners discusses magnesium testing and why a serum result has limitations when viewed on its own.
What should you check on a magnesium supplement?
If a qualified professional recommends supplementation, check the amount of elemental magnesium on the label rather than judging a product by the size of the compound name. Avoid assuming that a fashionable form is automatically superior for running; direct head-to-head performance evidence is limited.
The NHS warns that more than 400mg of magnesium from supplements over a short period can cause diarrhoea. It says 400mg or less a day from supplements is unlikely to cause harm for most people, but that is a safety ceiling rather than a target. Speak to a pharmacist or clinician before supplementing if you take medicines, have kidney problems, are pregnant or are under medical supervision.
Does RunStrong contain magnesium?
RunStrong does not provide a meaningful nutritional dose of magnesium. Magnesium stearate appears in the ingredient list as a manufacturing flow agent, but it is not an active magnesium supplement and should not be counted towards your daily intake.
RunStrong contains Carnipure® L-Carnitine L-Tartrate, Curcumin C3 Complex®, vegan Vitamin D3, Iron Bisglycinate and BioPerine®. It is designed as a daily nutritional foundation for runners, not as an electrolyte drink, cramp treatment or replacement for a magnesium supplement recommended by a healthcare professional.
Frequently asked questions
Should every runner take magnesium?
No. Most people should first assess their diet. Supplementation makes more sense when intake is inadequate or a healthcare professional identifies a specific need.
What type of magnesium is best for runners?
No form has been proven universally “best” for runners. Check the elemental magnesium dose, tolerability and professional advice rather than relying on marketing claims about absorption or recovery.
Will magnesium stop cramps during a race?
There is no good trial evidence showing that magnesium prevents exercise-associated cramps. Gentle stretching is the best-supported immediate response, followed by reviewing your individual fatigue, pacing, training and hydration factors.
Can I get enough magnesium from food?
The NHS says most people should be able to. Spinach, nuts, seeds, beans, lentils, wholegrains and wholemeal bread can all contribute.
Is the magnesium stearate in RunStrong a magnesium supplement?
No. It is used as a manufacturing aid and does not provide a meaningful nutritional magnesium dose.
Sources
- NHS: Vitamins and minerals — magnesium
- Zhang Y et al. Can Magnesium Enhance Exercise Performance? Nutrients. 2017. PMID: 28846654
- Heffernan SM et al. The Role of Mineral and Trace Element Supplementation in Exercise and Athletic Performance: A Systematic Review. Nutrients. 2019. PMID: 30909645
- Garrison SR et al. Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews. 2020. PMID: 32956536
- Miller KC et al. An Evidence-Based Review of the Pathophysiology, Treatment, and Prevention of Exercise-Associated Muscle Cramps. Journal of Athletic Training. 2022. PMID: 34185846
This article provides general information and does not replace personalised medical or nutritional advice. Speak to a GP, pharmacist or registered dietitian before using supplements to manage persistent symptoms or a diagnosed condition.