We built a hydration formula backward, starting from what sweat actually removes

Sweat is not water, and that changes what replacing it means

A litre of sweat leaving the body takes sodium with it. Drinking a litre of plain water restores the volume but not the sodium, so plasma sodium falls further than sweating alone would have driven it. The deficit that matters is not simply fluid; it is fluid and solute together, and they have to be replaced together.

Three consequences follow, and they compound rather than occur separately.

1. Circulating volume contracts

   Water leaves the plasma faster than sodium is replaced, so blood volume falls and the heart has less to move with each beat.

2. The sodium deficit accumulates

   In tropical-native runners, mean sodium loss reached 54 ± 27 mmol per hour in males and 39 ± 22 in females.² Over a long shift or a long event, that is a substantial withdrawal.

3. Cooling capacity drops

   A smaller plasma volume means less blood available to shunt to the skin. Core temperature keeps climbing at exactly the point the body most needs to shed heat.

So the design question is not how much water was lost. It is how much sodium went with it, how much of that can realistically be absorbed during the exposure itself, and what the drink has to look like for that absorption to happen at all.

The tropical case is about volume, not saltier sweat

It would be convenient to claim that people in Indian heat have distinctively salty sweat and therefore need a distinctive formula. The published data does not support that, and we are not going to argue it.

What the tropical studies show is more useful than the marketing version. Sweat sodium concentration in the tropics falls inside the ordinary global range. Across 556 athletes training at a wet-bulb globe temperature of 29.4 °C, whole-body sweat sodium averaged 43 ± 10 mmol/L in adults.³ In 166 tropical-native runners, individual values ranged from 11 to 80 mmol/L and did not differ between men and women.² In professional footballers training at 32 °C and 79% relative humidity, forearm sweat sodium was 26.7 ± 11.3 mmol/L — described by those authors as relatively low.⁴ The authors of the runner study concluded plainly that existing fluid-replacement guidelines apply to tropical-native athletes.²

The pressure comes from somewhere else. Sweat rate is high and sustained: 1.3 ± 0.5 L/h in male tropical runners, 0.9 ± 0.3 in females, with individuals spanning 0.3 to 2.5 L/h,² and 1.7 ± 0.5 L/h in footballers under hotter, more humid conditions.⁴ Multiply an ordinary concentration by a large and prolonged volume and the absolute sodium loss becomes large. That is the whole argument, and it survives scrutiny in a way the saltier-sweat claim would not.

Rehydration has to pass three gates, and most formulas open one

Fluid you have swallowed is not fluid you have absorbed, and sodium you have absorbed is not sodium you have kept. Between the bottle and the bloodstream sit three separate mechanisms, each with its own controlling variable.

These are not three marketing pillars dressed up as biology. They are three genuinely independent constraints, and they pull against each other: adding solute to improve gate one raises osmolality and can work against gate three. Getting all three right at once is a formulation problem, not an ingredient list.

Gate one: why there is glucose in an electrolyte drink

SGLT1 is a transporter in the wall of the small intestine that moves sodium and glucose across together. Water follows the gradient the pair creates. Sodium arriving without glucose is limited to slower routes, which is why an electrolyte drink with negligible carbohydrate is working against its own absorption.

The dose is a compromise between two opposing effects. Carbohydrate stimulates solute and water absorption, but carbohydrate concentration is also negatively related to water absorption once it raises luminal osmolality too far — a tension quantified across three decades of human intestinal perfusion studies.⁵ More glucose is not more absorption. Past the useful range it is simply more osmotic load working in the wrong direction.

HydraOsmo carries 8 g of glucose per 500 mL, a 1.6% solution. That is enough to drive co-transport and to keep the finished drink well inside the hypotonic range discussed in Section 6.

Gate two: the kidney decides what it keeps, using ubiquitin

Absorbed sodium is not retained sodium. The kidney adjusts, continuously, how much it reabsorbs — and the switch it uses is a ubiquitin ligase, which is not where most people expect a hydration story to go.

Under sodium stress, aldosterone rises. Aldosterone induces the kinase SGK1, which phosphorylates the ubiquitin ligase NEDD4-2 and so prevents NEDD4-2 from interacting with the epithelial sodium channel, ENaC.⁶ Ubiquitylation is the tag that pulls ENaC off the membrane for internalisation and degradation. Block the tagging and more channels stay in place; more channels in place means more sodium reabsorbed.⁷ The kidney also runs the reverse operation, deubiquitylating ENaC through an aldosterone-induced protease to the same end.⁸

This is the same ubiquitin machinery that governs protein turnover throughout the body, running here as a control system for salt and blood pressure. It is the reason our formulation work starts from regulatory biology rather than from an ingredient catalogue.

Gate three: the sachet is not the product, the solution is

What matters is not the ingredient list but the total concentration of dissolved particles once the powder is in water. That figure, osmolality, decides whether water crosses into the blood or is drawn the other way into the gut.

The evidence here is unusually clean. A 2022 systematic meta-analysis pooled 28 studies and 68 drink treatments to compare hypertonic, isotonic and hypotonic carbohydrate–electrolyte drinks against water, measuring change in plasma volume across up to 180 minutes of continuous exercise.¹ Hypotonic drinks preserved plasma volume best, at −6.3%, against −8.7% for isotonic, −7.4% for hypertonic and −7.5% for water. The hypotonic advantage over isotonic was 2.3 percentage points, with a 98.4% probability of superiority.¹

The threshold in that analysis matters more than the headline. Hypotonic means below 275 mOsmol/kg; isotonic begins at 275. A formula targeting 260–280 would straddle the boundary and could easily land on the wrong side of the finding it cites. Ours does not go near it.

Summing the dissolved species in one 500 mL serving — sodium 23.9 mmol, chloride from the salt architecture, potassium 4.6 mmol, magnesium 3.1 mmol, citrate roughly 3 mmol and glucose 44.4 mmol — gives approximately 95 mmol of particles, or around 185 mOsmol/kg once a normal osmotic coefficient is applied. That is comfortably hypotonic and close to the range where intestinal water absorption is most efficient.

We are publishing the calculated figure and labelling it as calculated. Real solutions come in below ideal arithmetic, flavouring and acidulants shift the total, and the salt architecture is not finalised. The batch specification will be set from a measured value on finished product, and it will be published here when it exists.

The formula, and the arithmetic behind each number

Nothing in this list is present for breadth, and nothing is present for the label. Each entry answers to a gate, or it does not appear.

Replacement percentages are calculated against measured sweat sodium loss rates in tropical-native runners and describe a single serving against one hour of exposure. Individual loss rates in that cohort ranged widely; these figures describe a population mean, not any individual.

What partial replacement means, and why we are not claiming more

One serving covers a little under half the mean hourly sodium loss of a male tropical runner. Two servings over an hour, at 1 L, cover about 89% of it. Across a longer exposure the arithmetic shifts again: 1.5 L over three hours delivers 72 mmol against a mean loss of about 162 mmol, so roughly 44%.

None of these is complete replacement, and complete replacement during exposure is not the goal. A drink salty enough to match loss litre for litre would not be drunk in the quantities required. The purpose is to keep the deficit from reaching the point where plasma volume, thermoregulation and performance start to fail, and to leave the remainder to food and post-exposure rehydration. The current position stand on fluid replacement makes the same point: it recommends individualised programmes and limiting body-mass loss to under 2%, rather than prescribing a single replacement fraction.⁹

What we left out, and why leaving it out was the harder decision

Most of these ingredients have real pathways. Having a pathway is not the test. The test is whether the pathway improves the outcome this product is being built to deliver, which is fluid and sodium retention during heat exposure.

• Citrulline. Converts to arginine and supports vasodilation. That is a blood-flow effect, which is a performance outcome, not a hydration one. If it belongs anywhere, it belongs in a separate performance formulation with its own trial.
• Beetroot and nitrate. Same category, same reasoning. Nitrate also adds regulatory complexity and shifts osmolality with source variability we would not be able to control batch to batch.
• Coconut water powder. Genuinely potassium-rich and commercially appealing, but elemental content varies with source and processing. We would rather specify a defined salt and know exactly what is in the sachet.
• Boron. Added elsewhere for mineral completeness. We found no evidence it accelerates rehydration or sodium absorption during acute heat exposure.
• Calcium, zinc and the rest of the complete-electrolyte set. Each adds osmotic particles at gate three in exchange for no demonstrated benefit at gates one or two. That is a bad trade in a formula whose central constraint is total dissolved solute.

Where one formula fits across very different exposures

The same three gates operate whether the exposure is a ninety-minute match or an eight-hour shift. What changes is drinking pattern and total volume, which is why one formula can cover the range without a different SKU for each use.

These are design envelopes drawn from published loss rates, not validated outcomes. They describe who the formula was built for. Section 10 describes what we have to do before we can say it worked.

What we still owe you: the measurements

Everything above is a design argument. A design argument is not evidence of an outcome, and the gap between the two is closed by testing, in this order.

1. Analytical specification

   Sodium, potassium, magnesium, chloride and glucose assayed by ion chromatography, ICP and HPLC. pH and osmolality measured at the recommended 500 mL dilution. This is what replaces the calculated osmolality figure in Section 6 with a real one.

2. Stability

   Accelerated storage at 40 °C and 75% relative humidity alongside real-time storage at 25 °C, with potency checked at 0, 3, 6, 9 and 12 months. This sets shelf life and storage conditions.

3. Gastrointestinal tolerance

   A crossover study, 12 to 20 participants, under controlled heat and exercise. Endpoints are nausea, cramping, fullness and palatability. A formula people will not finish drinking has no hydration effect at all.

4. Hydration efficacy

   The primary study: two to three hours of exercise under tropical heat conditions, crossover design, 24 to 30 participants, against water and against a marketed comparator. Endpoints are plasma volume, core temperature, fluid balance and time to fatigue.

Until stage four reports, we describe mechanism and dose. We do not describe outcomes.

What we will not claim

A claim that cannot survive being asked for its source should not be printed on a pack. These are ours, sorted by whether we can currently stand behind them.

What we can say now

• The formula was designed from measured sweat-loss data in tropical populations, with those sources named in the references below.
• It contains 550 mg sodium and 8 g glucose per 500 mL, a ratio chosen to engage sodium–glucose co-transport.
• Its calculated osmolality is hypotonic, the category that performed best for plasma-volume retention in a 2022 meta-analysis of 28 studies.¹
• Magnesium is held below the level at which magnesium salts commonly cause loose stools.

What we will not say until it has been tested

• Any multiple of hydration — no “5×”, no “100% cellular”, no “faster than water”. These have no defined endpoint and no measurement behind them.
• That HydraOsmo prevents hyponatremia. That is a clinical claim requiring a clinical study design.
• That it produces superior plasma-volume retention. The meta-analysis result belongs to a category of drinks, not to this product; inheriting it without our own comparative data would be borrowing someone else's evidence.
• That Indian or tropical physiology is categorically different. The published sweat data does not show that, and Section 2 says so.
• That the formula is engineered to any individual's sweat profile. Measured variation between individuals is too wide for that to be true of any single serving size.

Naming the boundary of what you know is not a weaker position than claiming past it. It is the only position you can still be standing in when someone asks to see the data.