The science of a hydration formula built for the heat

Most 'hydration' is sold on a vibe. We wanted the opposite: to start from the physiology and work forwards. What does a body in Dubai actually lose — sweating outside, then sitting in dry air-conditioning all day — and what would the ideal drink to replace it contain? Here is the science, said plainly, and the formula it points to.

First, what you actually lose.

Sweat isn't just water. By a wide margin, the two things you lose most are sodium and chloride — the salt in 'salty sweat', and they leave together. Everything else is a rounding error by comparison: potassium is a small loss, and magnesium and calcium smaller still. The sweat research is consistent on this — sodium and chloride dominate; the rest are minor.

Chloride is the forgotten one. It is the biggest *negative* ion you sweat out — often as much as the sodium by weight — and yet most hydration brands leave it off the label entirely. Replace the sodium but ignore the chloride and you have only put back half of the salt you actually lost.

Why water alone leaves a gap.

Drink only water after a long, sweaty stretch and you top up the *volume* but not what was dissolved in it. Sodium contributes to normal hydration — so putting it back, alongside the fluid, is the point. That is the gap an electrolyte drink fills: the minerals, not just the millilitres.

There is a second, quieter reason every proper rehydration drink in the world contains a *little* sugar. In your gut, sodium and glucose are absorbed together, and water follows them across — it is the principle behind oral rehydration solutions. You do not need much; a small amount does the job. Too much sugar and the drink turns into a soft drink that works against you. That is why SALT carries just 3 g — enough to help the sodium land and to taste like something you will finish, not enough to be the story.

The Goldilocks problem.

Here is where most products go wrong, in one of two directions. Wellness sprinkles put in so little sodium they can't meaningfully replace what heat-sweat takes — they taste lovely and do little. At the other extreme, athlete salt-bombs pack around 1,000 mg of sodium a serve, built for elite athletes losing litres of sweat an hour, and frankly punishing to drink every day.

The reference point hydration scientists actually use sits between them: the World Health Organization's rehydration standard is deliberately hypotonic — more *dilute* than your blood — because hypotonic drinks are the ones your gut takes on best. The lesson for a daily drink isn't to copy a medical rehydration salt (that is for illness); it is the shape of it — meaningful sodium, low sugar, kept dilute.

The Dubai twist: your body adapts.

This is the part that quietly argues against the salt-bomb for anyone who lives here. Spend a couple of weeks in real heat and your body acclimatises — and one of the things it does is make your sweat *less salty*, to hold on to sodium. The research puts the drop at around 40%: a long-term Dubai resident loses noticeably less sodium per litre of sweat than someone who flew in last week.

So the daily dose that makes sense for a heat-adapted body isn't the extreme one designed for an unacclimatised marathoner. It is a balanced one — enough to matter, not so much it is built for a body you don't have.

And the part nobody mentions: the air-con.

Step out of 42°C into a building chilled to 21°C and the air around you is *dry*. With every breath, your airways add moisture to it — and you breathe that water straight back out. It is not dramatic, but across a whole day in heavy air-conditioning it is a quiet top-up to everything else you are losing. The heat pulls fluid out of you outside; the AC keeps a slow pull going at your desk.

So what should be in the bottle?

Put the physiology together and the ideal *daily* heat-and-AC formula has a clear shape: a meaningful but not extreme dose of sodium (around 500 mg), chloride to genuinely match it, a modest amount of potassium (around 200 mg), a little magnesium, little or no calcium, and only a touch of sugar — all kept dilute and low-sugar. Effective enough to replace what the heat takes; gentle enough to drink every day.

One honest caveat: there is no single 'correct' number for everyone. Sweat — and how salty it is — varies a lot from person to person. A heavy outdoor worker needs the upper end; someone mostly at a desk, the lower. Any one formula is a sensible middle, not a prescription. This is general guidance, not medical advice.

How SALT is built.

We built SALT to that shape on purpose. One sachet in 750 ml puts back 500 mg sodium, around 600 mg chloride, 200 mg potassium and 60 mg magnesium, with 3 g of sugar — in a full bottle, kept comfortably dilute. The chloride is the part most brands skip; we put it on the label because it is half the salt you actually lose.

A detail we are quietly proud of: our sodium is set slightly higher than the chloride on purpose — some of it comes from sodium citrate, not just table salt, the same gentle, buffering source the WHO rehydration standard uses. It rounds the taste and lets us get the sodium right without over-salting the chloride.

The result is the balance the science points to: roughly double the salt of a typical wellness sachet, but a fraction of an athlete salt-bomb. Alongside the sodium, potassium contributes to normal muscle function, and magnesium contributes to normal muscle function and to normal energy-yielding metabolism. Three jobs, three minerals, the amounts on the pack.

The short version.

You lose mostly sodium and chloride; water alone only replaces the volume; a little sugar helps the sodium land; the dose should be meaningful but not extreme — especially once you are heat-adapted — and kept dilute. That is not a marketing position. It is what the physiology says, and SALT is built to it.

Authorised health-claim references: Sodium contributes to normal hydration. Potassium contributes to normal muscle function. Magnesium contributes to normal muscle function. Magnesium contributes to normal energy-yielding metabolism.