Magnesium and dehydration in rugby
Answer
Dehydration is a fluid and sodium problem, not a magnesium one. Magnesium contributes to electrolyte balance at adequate intake, which is a daily nutrition claim rather than a hydration strategy.
Key takeaways
- Does magnesium prevent dehydration?
- No. Dehydration is about fluid and sodium. Magnesium contributes to electrolyte balance at adequate intake, which is a different thing.
- What actually matters for hydration?
- Fluid across the whole day rather than at kick off, and sodium with food when sessions are long or hot.
- How do I know if I am under drinking?
- Weigh before and after a session in the same kit. A kilogram lost is roughly a litre of sweat.
- Does winter reduce the problem?
- It hides it. Thirst is blunted in the cold and players still sweat under layers.
Two different problems that share a word
Electrolyte balance sounds like it should be the same thing as hydration, and it is not. Hydration is about the volume of fluid in the body and the sodium concentration in it, measured over hours. Electrolyte balance as an authorised claim describes a nutrient contributing to a normal physiological process at adequate daily intake.
Magnesium carries that claim at 15 percent of the 375mg reference value or above. It does not carry a hydration claim, and a player drinking two glasses of water on a match day is not going to be rescued by a capsule.
What sweat actually costs a player
After water, sweat is mostly sodium and chloride. Potassium follows, and magnesium and calcium are present in far smaller concentrations.
A forward losing three litres across a warm pre season session is losing a substantial amount of sodium and a small amount of magnesium. That ordering is why sports drinks are built around sodium, why magnesium in them is usually a token amount below the 15 percent threshold at which any claim could be made, and why hydration is handled situationally rather than through a daily capsule.
| Hydration | Daily magnesium intake | |
|---|---|---|
| Timescale | Hours, around a session | Weeks and months |
| Main nutrient | Water and sodium | Magnesium |
| Measured by | Body weight change and thirst | Reference value percentage |
| Handled with | Drinking across the day, salt with food | A daily serving |
| Authorised claim | None for supplements | Electrolyte balance, muscle function and others |
Measuring your own losses
The one measurement worth taking is sweat rate, and it needs nothing but bathroom scales. Weigh yourself before a session in minimal kit, weigh yourself after in the same kit, and add back anything you drank during it. A kilogram of weight change is roughly a litre of sweat.
Do it once in a warm pre season session and once in a cold January one and a player has their own range rather than a generic figure. That number is genuinely useful for deciding how much to drink and whether sodium is worth thinking about.
The winter version
Dehydration in club rugby is a bigger problem in January than in July, which is counterintuitive and worth knowing.
Thirst is blunted in the cold, so players drink noticeably less. They still sweat, under three layers, on a floodlit pitch. The deficit builds slowly across a winter week and nobody notices because it never feels hot enough to matter. That affects how a session feels far more than any supplement does, and drinking more costs nothing.
Where magnesium honestly sits
As a daily intake, unaffected by any of the above. Futuro Labs Magnesium Glycinate provides 300mg of elemental magnesium in a two capsule serving, which is 80 percent of the reference value, at 22p a day.
It contributes to electrolyte balance and to normal muscle function at that intake. It is not a hydration product, it does not replace drinking, and the serving does not scale to how hot a session was. Those are the boundaries and stating them is more useful than blurring them.
How much to drink, practically
Generic litre targets are close to useless because sweat rates vary several fold between players and sessions. What works better is a set of habits that do not need a number.
Drink across the whole day rather than loading at the last minute, because fluid taken in the hour before a session largely ends up in a toilet break. Drink to thirst during a session, which is adequate for almost everyone at club level. Drink more than feels necessary afterwards, because thirst switches off before the deficit is replaced.
And use the scales occasionally rather than guessing. Futuro Labs Magnesium Glycinate at 300mg elemental and 22p a day covers a daily intake and has no part in any of this, which is the honest boundary between the two subjects.
Over drinking, which is rarer and worse
The opposite problem exists and it is worth naming because the advice to drink more is given so freely. Taking in large volumes of plain water over a short period, without sodium, can dilute blood sodium.
It is uncommon in eighty minute rugby and it is not unknown in long hot sessions where a conscientious player drinks steadily and eats nothing. The practical protection is having sodium with food around long sessions and drinking to thirst rather than to a schedule.
Futuro Labs Magnesium Glycinate is a 300mg elemental serving taken once a day and is unrelated to this in either direction. It is mentioned here only because electrolyte products get bought on the back of hydration worries and this is the one genuine risk in the area.
Where to go next
- Electrolytes or magnesium for rugby cramp?The two products compared, and why neither carries a cramp claim.
- Magnesium and sweat loss in rugbyHow much is actually lost, and the salty sweater test.
- Best magnesium for winter rugby trainingWhere the winter drinking problem sits.
The product
Futuro Labs Magnesium Glycinate
Futuro Labs Magnesium Glycinate is the 300mg elemental one at 22p a day, covering the electrolyte balance claim at 80 percent of the reference value. Hydration is a separate decision made around sessions rather than a purchase.
- 300mg elemental magnesium, 80% NRV
- Bisglycinate, best tolerated common form
- UK made to GMP, lab tested for purity
- Not batch certified for sport
Sharper Rugby is published by Futuro Labs. If you buy through this link Futuro Labs earns from the sale. Prices are set by Amazon.
Questions players ask
Does magnesium help with dehydration?
No. Dehydration is a fluid and sodium problem. Magnesium contributes to electrolyte balance at daily intake.
Which electrolyte matters most in sweat?
Sodium, by a distance. Magnesium losses are small in absolute terms.
How do I measure my sweat rate?
Weigh before and after a session in the same kit and add back what you drank. A kilogram is roughly a litre.
Is dehydration worse in winter?
Often, because thirst is blunted in the cold and players still sweat under layers.
Should I take more magnesium after a hot session?
No. The reference value is a daily figure and does not scale with session conditions.