How much magnesium do you lose in sweat?
Answer
Small amounts in absolute terms. Sweat is mostly water and sodium, and magnesium concentration is low enough that no consumer method estimates the loss.
Key takeaways
- How much is lost?
- Small amounts relative to sodium, which is the largest electrolyte loss by a wide margin.
- Can it be measured?
- Sweat volume can be, with scales. Magnesium concentration cannot outside a laboratory.
- Does it change the serving?
- No. The reference value is a daily figure and does not scale with sweat.
The ordering in sweat
After water, sodium and chloride dominate. Potassium follows, then magnesium and calcium in far smaller concentrations.
That ordering is 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. In that context it is a marketing ingredient rather than a functional one.
What can and cannot be measured
Sweat volume is measurable with bathroom scales and it is worth knowing. Sodium concentration has a visible proxy in the white marks a salty sweater leaves on kit.
Magnesium has neither. There is no equivalent test, and the practical response is covering the daily intake rather than trying to match losses. Futuro Labs Magnesium Glycinate does that at 300mg elemental and 22p a day.
Why the figure varies so much
Sweat composition differs between people, between sites on the body and with sweat rate itself, which is why published figures for magnesium in sweat span a wide range. Collection method affects results as well. That variation is another reason the practical response is covering a daily intake rather than trying to match an estimated loss.
What is worth measuring instead
Sweat volume, once in a warm session and once in a cold one, so a player has their own range rather than a generic figure. That number is genuinely useful for fluid decisions and for judging whether sodium is worth thinking about around long hot sessions. Magnesium losses cannot be estimated the same way, which is why the daily intake is the practical lever.
The full version
- Magnesium and sweat loss in rugbyThe full version, including salty sweaters and how to measure sweat rate.
- Is magnesium lost in sweat?The short answer on the losses themselves.
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 in sweat?
A low concentration relative to sodium, which dominates after water.
Can I test my losses?
Not outside a laboratory. Sweat volume can be measured with scales.
Is the magnesium in sports drinks useful?
Usually below the threshold at which any claim could be made.