Does a bigger rugby player need more magnesium?
Answer
No. No UK reference value for magnesium scales with body weight. A 120kg prop and a 75kg winger are pointed at the same figure, and a larger player usually eats more so often takes in more anyway.
Key takeaways
- Does the target scale with body weight?
- No. Neither the 375mg labelling reference value nor the UK dietary reference values adjust for body mass.
- Why does it feel like it should?
- Protein targets do scale with body weight, so players reasonably assume minerals work the same way. They do not.
- Does a bigger player lose more?
- In sweat, usually yes. But they also typically eat more food, so intake rises alongside losses.
- Should a bigger player take a bigger dose?
- No. A 300mg elemental serving covers 80 percent of the labelling reference value for anyone.
The direct answer
No reference value for magnesium in the UK is expressed per kilogram of body weight. The labelling nutrient reference value is 375mg a day. The UK dietary reference values are 300mg for adult men and 270mg for adult women. None of those adjusts for size.
So a 120kg tighthead and a 75kg winger are pointed at the same number, and any product or advice offering a milligram per kilogram magnesium figure has made it up.
Why the assumption is so common
Because protein does scale. Protein targets for athletes are routinely given per kilogram of body weight, commonly in the range of 1.6 to 2.2 grams per kilogram, and every player has heard that framing.
Minerals are set differently. They are population intake recommendations derived from balance studies and intake data, not scaled to individual size. Carrying the protein framing across to magnesium is a completely understandable mistake and it is still a mistake.
| Nutrient | Scales with body weight? | Typical basis |
|---|---|---|
| Protein | Yes | Grams per kilogram per day |
| Magnesium | No | A single adult reference value |
| Fluid | Partly | Driven by sweat rate rather than mass alone |
| Sodium | Partly | Driven by sweat volume and concentration |
| EPA and DHA | No | A fixed 250mg claim threshold |
The sweat argument, and its limit
A larger player usually sweats more in absolute terms, and magnesium is lost in sweat. That is a real argument that a bigger prop is getting through more.
It has a counterweight. A larger player usually eats considerably more food, and magnesium comes from food. A 120kg forward eating 4,000 calories is taking in more magnesium than a 78kg winger eating 2,600, from exactly the same diet. The two effects push against each other, which is part of why no scaled figure exists.
What this means in practice
One serving, same product, across the squad. Futuro Labs Magnesium Glycinate provides 300mg of elemental magnesium in a two capsule serving, which is 80 percent of the 375mg labelling reference value whoever takes it.
There is also a ceiling worth knowing. UK guidance sets 400mg a day from supplements specifically, based on the laxative effect of high supplemental doses. A bigger player doubling a serving on the assumption that size justifies it is heading towards that figure for no benefit.
The one place size genuinely matters
Futuro Labs Magnesium Glycinate is dosed for the reference value rather than for a body weight, which is why one product covers a whole squad.
Fluid and sodium. Sweat rate varies enormously between players and a large forward in a warm pre season session can lose several litres.
That is a hydration question answered during and around sessions rather than an intake question answered by a daily capsule, and it is where an electrolyte drink has a genuine role that magnesium does not.
The one figure that does scale
Protein is the exception that creates the confusion, so it is worth setting out properly. Athlete protein targets are routinely given per kilogram of body weight, commonly between 1.6 and 2.2 grams per kilogram per day.
For a 78kg winger that is roughly 125 to 172 grams. For a 118kg prop it is roughly 189 to 260 grams. Those are genuinely different targets and a prop who eats like a winger will fall short of them.
Magnesium does not work that way and neither do the other nutrients covered on this site. The EPA and DHA claim threshold is a flat 250mg for everyone. The magnesium reference value is 375mg for everyone. Carrying the protein logic across is the single most common nutrition mistake in a rugby changing room, and it costs money in doubled servings that do nothing.
Where the doubling instinct comes from
Players do not arrive at doubling a serving randomly. It comes from three reasonable assumptions that all turn out to be wrong for minerals.
That bigger bodies need proportionally more of everything, which is true for energy and protein and not for micronutrients. That harder training raises every requirement, which raises losses without raising recommendations. And that if a normal dose is safe, a double dose must be safer than falling short, which ignores that supplemental magnesium has a guidance ceiling of 400mg a day precisely because higher intakes cause problems.
One serving of Futuro Labs Magnesium Glycinate provides 300mg of elemental magnesium and leaves 100mg of headroom against that ceiling. Two servings clears it, for no benefit any reference value supports.
Where to go next
- How much magnesium does a rugby player need?Both reference figures, food sources and the supplemental guidance level.
- Electrolytes or magnesium for rugby cramp?Where sweat and sodium genuinely do matter.
- Best magnesium for prop forwardsThe same question from the position that asks it most.
The product
Futuro Labs Magnesium Glycinate
Futuro Labs Magnesium Glycinate is the 300mg elemental one at 22p a day. One serving covers 80 percent of the labelling reference value whoever takes it, which is why the same product suits the whole squad.
- 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 a 120kg player need more magnesium than a 75kg player?
No. No UK reference value for magnesium scales with body mass.
Why does protein scale but magnesium not?
Protein targets are set per kilogram. Mineral reference values are single population figures.
Does a bigger player lose more in sweat?
Usually yes, but they also typically eat more food, so intake rises alongside losses.
Should a forward double the serving?
No. UK guidance sets 400mg a day from supplements, and doubling heads towards that for no benefit.
Where does size genuinely matter?
Fluid and sodium, which are hydration questions rather than daily intake ones.