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Magnesium and Sport: How Much, When to Take It, and Who Actually Needs It

300–350 mg of elemental magnesium a day, food included — and training does not raise that. Where it comes from, why 500 mg of citrate is only about 80 mg of magnesium, what the sports differences really are, and why cramps are not a diagnosis.

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Most athletes do not need a magnesium supplement. The ones who do usually need far less than the tub suggests — and the number on the front of it is rarely the number that matters.

For healthy adults the daily reference value is roughly 300–350 mg of elemental magnesium, and training does not raise it. No official body sets a higher magnesium requirement for athletes. What training changes is the risk of falling short: more food passing through, more sweat, and — for anyone eating in a deficit — less room for the seeds, wholegrains, legumes and greens that carry most of the magnesium in a normal diet.

In short: Cover magnesium from food first; a normal mixed diet usually gets there. If you supplement, 100–250 mg of elemental magnesium a day alongside food is the useful range, taken with a meal and split if your stomach objects. The EU's upper level for supplemental magnesium is 250 mg a day on top of food. Timing is preference, not physiology. And cramps are not proof of a deficiency.

Sources checked September 2026: the D-A-CH reference values used by the Swiss BLV, the EFSA dietary reference values for magnesium, the EU Scientific Committee on Food upper level, the NIH Office of Dietary Supplements factsheet and the Cochrane review on magnesium for muscle cramps. General information, not medical advice.

How much magnesium per day

Magnesium is a cofactor in hundreds of enzyme reactions, including the ones that turn food into ATP and the ones that let a muscle fibre relax again after it has contracted. That is why it gets marketed at athletes: every word in that sentence sounds like performance.

The reference values, though, are set for the whole population and not for training:

The ranges differ because the committees used different methods, not because one of them knows something the others do not. Take 300–350 mg as the working target if you are in Switzerland, and treat it as a target for total daily magnesium — food included, not a supplement dose.

Where your magnesium actually comes from

Magnesium sits in the middle of chlorophyll and in the germ of a grain, so the foods that carry it are the unrefined ones. A handful of pumpkin seeds does more than most capsules.

Magnesium per portion

Pumpkin seeds

30 g · ~150 mg

Spinach, cooked

200 g · ~120 mg

Oat flakes

60 g · ~80 mg

Almonds

30 g · ~80 mg

Dark chocolate

30 g · ~70 mg

Wholegrain bread

2 slices · ~60 mg

Two more everyday sources are easy to miss. Legumes contribute 50–70 mg per cooked portion, and mineral water carries anywhere from almost nothing to well over 100 mg per litre — the label states it, and it is the cheapest magnesium there is.

Where intake genuinely tends to fall short is more specific than "athletes": a diet built on refined carbohydrates with little in the way of seeds, nuts, wholegrains and green vegetables; an aggressive or prolonged calorie deficit; chronic gastrointestinal disease or malabsorption; heavy alcohol use; long-term use of certain medicines, proton-pump inhibitors and some diuretics among them; and poorly controlled diabetes. If none of those describes you, a supplement is unlikely to be the thing standing between you and your next personal best.

Does your sport change the dose?

The dose, essentially no. The probability that you are short, and the consequences of being short, yes.

Sweat is the argument you will see most often, so it is worth being precise: magnesium is present in sweat, but at a low concentration relative to sodium, and the amounts lost even over a long hot session are small next to a 300 mg daily intake. That is why no reference-value committee has set an athlete-specific magnesium figure. Sodium is a different story, and belongs to a different article.

Three numbers that get confused

Almost every bad magnesium decision comes from mixing up three separate quantities.

1. 1Daily reference value — total intake300–350 mg/day

   Food plus any supplement. This is the target, not a supplement dose

2. 2Typical useful supplement amount100–250 mg/day elemental

   Only ever meant to close a gap food left open

3. 3EU upper level for supplements250 mg/day, on top of food

   Set by the EU Scientific Committee on Food; the US figure is 350 mg

Read the ladder from the top down and the practical rule falls out: if your food already brings 250 mg, a 400 mg capsule is not topping you up, it is overshooting a target you had almost reached — and it is above the level the EU considers tolerable for supplemental magnesium. Overshoot does not make you stronger; it makes your stomach unhappy.

Elemental magnesium, and how to read a label

This is the single most useful thing in the article. Magnesium is always sold as a compound — citrate, bisglycinate, oxide, carbonate — and the magnesium itself is only a fraction of the compound's weight. A tub that shouts "500 mg magnesium citrate" is not offering 500 mg of magnesium.

What the front says

500 mg magnesium citrate

The weight of the whole compound, magnesium plus citric acid

→

What you absorb as magnesium

~80 mg elemental magnesium

Roughly 16% of magnesium citrate by weight is magnesium itself

Same capsule, two very different numbers — the back of the pack carries the one that counts

So: ignore the front of the tub, find the nutrition panel, and read the milligrams of magnesium per daily portion. Every number in this article — and in the reference values — is elemental magnesium.

When to take it, and which form

Timing. There is no established performance reason to take magnesium before, during or after training, and no strong evidence that evening dosing is physiologically better than morning dosing. Take it when you will actually remember — with food, which is gentler on the stomach than an empty one.

Splitting. Tolerance, not absorption, is the argument for splitting. Large single doses of the readily dissociable salts are the usual cause of loose stools; two portions of 100 mg are easier on most people than one of 200 mg. Absorption is also proportionally somewhat better from smaller doses, which is a second small reason to split rather than stack.

Form. The well-dissolving organic salts — citrate, lactate, bisglycinate, malate — are absorbed more completely than magnesium oxide, which is poorly absorbed and the most likely to act as a laxative. That does not make any one of them "the best form", and the differences between citrate and bisglycinate are far smaller than the marketing implies. Magnesium oxide is the outlier worth avoiding if you have had gut trouble; between the rest, pick on tolerance and price.

Cramps, sleep, soreness, performance

Five claims, sorted by what the evidence supports.

• "Cramps mean a magnesium deficiency." No. Exercise-associated cramps are most consistently linked to neuromuscular fatigue — new intensity, new duration, late in a hard session — rather than to a single mineral. The Cochrane review on magnesium for skeletal muscle cramps found no clinically meaningful benefit in older adults and judged the evidence for exercise-associated cramps too limited to support its use. If you cramp, look at pacing, session novelty, heat, sodium and fluid before you look at magnesium.
• "Athletes automatically need a high dose." No committee that sets reference values agrees. Higher food intake generally brings more magnesium with it.
• "Magnesium in the evening improves everyone's sleep." The trials are small, mostly in older adults with insomnia, and mixed. It is reasonable to try and unreasonable to promise.
• "More magnesium means better performance." Correcting a genuine shortfall can help; adding magnesium on top of an adequate intake has not been shown to improve performance. The NIH summary of the exercise literature describes the results as mixed.
• "Citrate / bisglycinate / oxide is clearly the best form." Only oxide is clearly different, and not in a good way. The rest are close enough that tolerance decides.

One honest note on diagnosis: serum magnesium is the test most people get, and it correlates poorly with total body magnesium, because the body holds most of it in bone and inside cells. A normal serum value does not fully rule out a shortfall, and an abnormal one is a reason to see a doctor rather than to buy a tub.

That is also the useful comparison to keep in mind: magnesium sits low on the list of supplements worth thinking about. Our guide to the supplements that actually work sorts the short list from the long one, and creatine is the one where the dose genuinely repays attention.

Four athletes, four answers

Illustrative scenarios, not individual advice.

• A lifter eating a varied surplus. Oats, nuts, wholegrains and greens are already in the diet, and total intake is high. No supplement. The training log is where the gains are.
• A runner on high mileage and a restricted diet. The credible risk case: the volume is up, the food is down, and variety is the first casualty. Add seeds, legumes and wholegrains first; if the diet cannot get there, 100–200 mg elemental with dinner is reasonable — and the deficit itself deserves a look.
• A Hyrox athlete who cramps in the compromised runs. Cramping in exactly the hardest, most novel part of the race points at fatigue and pacing, not at a mineral. Check the run–station transitions and sodium; if cramps persist outside training, that is a conversation with a doctor.
• Someone whose stomach hates their current supplement. Almost always the dose size or magnesium oxide. Halve the portion, move it to a meal, or switch to a well-dissolving salt — in that order.

Safety, medication and when to ask a doctor

Everything above is for healthy adults.

• Kidneys. Impaired kidney function is the one situation where magnesium supplements carry real risk, because excretion is how the body handles excess. Do not supplement without medical advice.
• The usual side effect. Diarrhoea, cramping and nausea from supplemental magnesium are dose-related, not dangerous, and resolve when the dose comes down. Magnesium from food does not do this.
• Medication spacing. Magnesium can interfere with the absorption of several drug classes. Bisphosphonates and tetracycline or quinolone antibiotics should be separated from magnesium by at least two hours — and in the case of those antibiotics, considerably longer after. If you take any regular medication, check with the pharmacy that dispensed it.
• Not a diagnosis. Persistent cramps, unexplained fatigue, palpitations, numbness or tingling belong with a doctor. They are not a reason to self-treat with a mineral.
• Pregnancy, breastfeeding and chronic illness. The reference values shift and the interactions matter more. Ask, rather than generalise from an article.

Frequently asked questions

How much magnesium should I take per day as an athlete?

Aim for 300–350 mg of elemental magnesium in total per day, food included — training does not raise that target. If food leaves a gap, 100–250 mg a day from a supplement closes it, and the EU upper level for supplemental magnesium is 250 mg on top of what you eat.

Is it better to take magnesium in the morning or in the evening?

Whichever you will keep up. There is no established performance argument for training-day timing and no strong evidence that evening dosing works better than morning dosing. With a meal is gentler on the stomach, and splitting the day's amount in two makes loose stools less likely.

Does magnesium help against cramps?

Usually not. The Cochrane review found no clinically meaningful benefit for muscle cramps and too little evidence to recommend it for exercise-associated cramps. Pacing, unfamiliar intensity, heat, sodium and fluid are the more productive places to look.

Magnesium citrate or bisglycinate — which is better?

Both are well-absorbed organic salts and the difference between them is small; choose on tolerance and price. The meaningful comparison is against magnesium oxide, which is poorly absorbed and the most likely to upset your stomach.

The bottom line

• 300–350 mg of elemental magnesium a day, food included. Training does not raise the target; it raises the chance you miss it.
• Food first, and it usually works. Seeds, wholegrains, legumes, greens and the right mineral water get most people there without a supplement.
• Read the back of the tub. 500 mg of citrate is about 80 mg of magnesium. Compare products on elemental magnesium per daily portion, nothing else.
• Cramps are not a magnesium diagnosis. Neither is poor sleep. Correct a real shortfall; do not expect an effect on top of an adequate intake.

General information only: This article is general nutrition and training information and is not medical advice. The doses discussed are for healthy adults. If you have kidney disease, are pregnant or breastfeeding, take regular medication, or have persistent symptoms, talk to your doctor or a qualified healthcare professional before supplementing.

Sources

1. DGE / D-A-CH: reference values for magnesium intake — the values the Swiss BLV applies
2. Swiss Federal Food Safety and Veterinary Office (BLV): nutrient reference values for Switzerland
3. EFSA (2015): Scientific opinion on dietary reference values for magnesium (Adequate Intake 350 mg men / 300 mg women)
4. EU Scientific Committee on Food (2001): opinion on the tolerable upper intake level of magnesium (250 mg/day from supplements)
5. NIH Office of Dietary Supplements: magnesium factsheet (forms and absorption, medication interactions, serum testing, exercise literature)
6. Garrison et al., Cochrane Database of Systematic Reviews (2020): magnesium for skeletal muscle cramps