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How much sodium do you actually need?

Electrolyte products sell you four or five minerals. Only one of them changes what happens to you in a long, hot session — and unlike fluid, it's worth replacing close to what you lose.

Last updated September 2026

Why sodium is different from fluid

With fluid, replacing most of your losses is enough — finishing a session slightly down is normal and fine. With sodium it's close to the opposite. Under-replacing sodium while drinking plenty of water is exactly the combination that leads to hyponatremia. The sodium in your blood gets diluted twice over: once by the water you drink, and once by the salt you've sweated out and not put back.

That's the asymmetry worth remembering. Being a litre down on fluid at the finish is unremarkable. Being significantly down on sodium while topped up on water is the scenario that ends races and occasionally ends up in a medical tent.

The variation between people is huge

Sweat sodium concentration ranges from roughly 200mg to 2000mg per litre — a tenfold difference. Two people on the same ride, sweating the same volume, can have wildly different sodium needs. Unlike sweat rate, this one barely shifts with training or acclimatisation. It's largely just how you're built.

Put the two variables together and the spread gets dramatic. A light sweater with dilute sweat might lose 200mg of sodium in an hour. A heavy sweater with salty sweat, in the heat, can lose well over 2000mg in the same hour. No single electrolyte tablet dose serves both of those athletes.

How to spot the high end without a lab test

Sweat sodium testing exists and is genuinely accurate, but you can place yourself fairly well for free. Signs that point to salty sweat:

• White marks on dark kit after a session dries — the clearest signal there is.
• Sweat that stings your eyes or tastes noticeably salty.
• Gritty residue on your skin, cap or sunglasses after a hot session.
• A tendency to cramp in heat, particularly late in long events.

If several of those describe you, plan toward the upper end of your sodium range rather than the middle. The "salty sweater" option in the My Fuel Plan sweat test raises your target accordingly, so you're not doing that arithmetic yourself.

Roughly where to aim

Two things to note when reading product labels. First, many list sodium chloride (salt) rather than sodium — and salt is only about 40% sodium by weight, so 1g of salt gives you roughly 400mg of sodium. Second, standard sports drinks are relatively low in sodium, usually a few hundred milligrams per litre. Hitting 1000mg an hour from a normal sports drink alone is not realistic; that's what the concentrated tablets and high-sodium mixes are for.

What about potassium and magnesium?

Both get marketed heavily, and both appear on the front of the packet. But you lose far less of them in sweat — potassium at roughly a tenth of sodium levels, magnesium less still. A normal diet covers them for most people, and there's little evidence that topping them up mid-session changes anything. Sodium is where the attention belongs.

The same goes for cramp products built around magnesium. If cramping is your problem, the causes are more likely elsewhere — which is worth being honest about.

Sodium and cramping: the honest version

Cramp causes are still genuinely debated. Sodium loss and dehydration get blamed most often, but muscle fatigue and simply going harder than your training supports may matter more. The strongest case for sodium is the specific combination of a known salty sweater cramping repeatedly in heat late in long events — there, more sodium is well worth trying.

What it won't do is fix cramps caused by starting too fast. If you cramp at 70 minutes into a race you went out hard in, no electrolyte product is the answer to that.

Pre-loading before a hot event

Sodium pre-loading works best around 12–15 hours before the start — salty foods or added salt at meals the evening before, rather than a large dose on race morning. It's particularly worth doing if you're a salty sweater or the forecast is hot. Like everything else in fuelling, try it in training first; discovering how your stomach responds to a deliberately salty dinner is not a race-eve experiment.

General information for healthy adults, not individual medical or dietary advice. If you have a condition affected by sodium intake, or take medication that is, speak to a doctor before changing it.