Is magnesium lost in sweat?
Answer
Yes, and in small amounts relative to sodium. Sweat is mostly water and sodium, with magnesium present in far smaller concentrations.
Key takeaways
- Is it lost in sweat?
- Yes, but in small absolute amounts. Sodium is the electrolyte lost in by far the largest quantity.
- Does that raise the target?
- No. The 375mg reference value does not scale with sweat losses.
- What should a heavy sweater prioritise?
- Fluid and sodium around sessions, which is a hydration decision rather than a daily intake one.
What sweat is actually made of
After water, sweat is mostly sodium and chloride. Potassium follows, and magnesium and calcium are present in far smaller concentrations.
That ordering explains why sports drinks are built around sodium, and why the magnesium in them usually sits below the 15 percent NRV threshold at which any magnesium claim could be made. It is a marketing ingredient in that context rather than a functional one.
What the losses actually mean
Small daily losses accumulate across a season of training four times a week, which widens the gap between what a player takes in and what they use.
It does not create a separate athlete reference value, and none exists. Futuro Labs Magnesium Glycinate covers 80 percent of the 375mg reference value in one two capsule serving at 22p a day, which is the same serving whether a session was hot or cold.
The measurement you can actually take
Sweat rate needs nothing but bathroom scales. Weigh before a session in minimal kit, weigh after in the same kit, and add back anything drunk during it. A kilogram of weight change is roughly a litre of sweat. That number is useful for fluid and sodium decisions and it does not translate into a magnesium figure.
The full version
- Magnesium and sweat loss in rugbyHow to measure your own sweat rate and what the salty sweater test shows.
- Magnesium and dehydration in rugbyWhere hydration and daily intake genuinely separate.
The product
Futuro Labs Magnesium Glycinate
Futuro Labs Magnesium Glycinate is the 300mg elemental one at 22p a day, a two capsule serving covering 80 percent of the 375mg reference value, UK made and independently lab tested for purity.
- 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
How much magnesium is lost in sweat?
Small amounts relative to sodium, which is the largest electrolyte loss by a distance.
Should I take more after a hot session?
No figure supports scaling a daily intake to session conditions.
Can I measure my losses?
Sweat volume yes, with scales. Magnesium concentration no, not outside a laboratory.