Electrolytes: When You Need Them and When It Is Marketing

Shelves of electrolyte powders have grown out of sports nutrition into a category of their own — sold now for morning water, for hangovers, and simply for "energy". Yet the physiology is built so that a healthy person eating normal food almost never needs them: the body defends these concentrations more tightly than nearly anything else, and it does so for free. Here is where the physiology ends and the marketing begins.

What they do#

Electrolytes are minerals that dissociate into charged ions in solution. The charge is the point: the difference in sodium and potassium concentrations across the cell membrane creates the resting potential, and with it every nerve impulse and every muscle contraction, the heart included.

Electrolyte	Main role	Daily reference	Where to get it
Sodium	Extracellular fluid volume, nerve conduction	1.5–2.3 g (4–6 g of salt)	Salt, bread, cheese, prepared food
Potassium	Cell potential, cardiac function, blood pressure	3.5–4.7 g	Potatoes, pulses, bananas, spinach, dried apricots
Chloride	Acid-base balance, gastric acid	about 2.3 g	Table salt
Magnesium	Over 300 enzymes, neuromuscular transmission	300–400 mg	Nuts, seeds, whole grains, dark chocolate
Calcium	Muscle contraction, bone, clotting	1,000 mg	Dairy, sardines, tofu, leafy greens

The irony is that for most people the real problem runs the other way. Western diets carry a sodium surplus — 9–12 g of salt a day against a recommended 5. Potassium, meanwhile, is short almost everywhere: it lives in vegetables, pulses and fruit, which people eat too little of. It is the sodium-to-potassium ratio, rather than sodium alone, that maps most closely onto blood pressure.

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What sweat takes with it#

Sweat is not just water. It carries sodium and chloride and, in smaller quantities, potassium, magnesium and calcium. But the proportions are nothing like plasma: sweat is hypotonic, meaning it holds relatively more water than salt.

The spread between people is enormous. Normative data put sweat sodium anywhere from 200 to 2,000 mg per litre. At a sweat rate of one litre an hour, that is the difference between a pinch of salt and a gram and a half.

Weight, kg

Age, years

Sex

MaleFemale

Exercise per day: 45 min

IntensityLight — walking, yogaModerate — running, gym, cyclingHard — heat, racing, long cardio

Climate and conditionsCool, under 15 °CTemperate, 15–25 °CHot, 25–32 °CVery hot or humid, above 32 °C

Waking hours

To drink per day

2.3 Lroughly 9 glasses of 250 ml

Total water for the day is 3.0 L, of which about 0.7 L arrives in food: vegetables, fruit, soups, porridge.

Where it comes from

Baseline for your body mass

2,475 ml

Sweat losses in training

525 ml

Across the day

About 146 ml per waking hour — roughly a glass every ninety minutes across 16 h.

The check that needs no calculator

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Urine colour tracks concentration better than any sensation except thirst. Shades on the left are normal, on the right show a deficit. The first morning sample is always darker, and that means nothing.

📐 For comparison

EFSA recommends 2.5 L of total water a day for your sex; the US Institute of Medicine says 3.7 L. Both figures are medians of what healthy people actually drink, not a measured requirement. The gap between them is the honest measure of how precise any “water norm” can be.

💡 What does not count as dehydration

Coffee and tea count towards your daily balance: at habitual doses the diuretic effect of caffeine does not exceed the volume you drank. The “eight glasses” rule has no source in the research literature. Thirst, on the other hand, works: in a healthy adult with access to water it fires well before any meaningful deficit.

This calculation does not apply in heart or kidney failure, on diuretics, or in any condition where fluid is deliberately restricted — there the target comes from a doctor and can be considerably lower. Too much water is dangerous too: hyponatraemia develops when intake persistently outruns the kidneys. 800 ml/h is the reference ceiling for clearance.

When electrolytes genuinely matter#

Efforts beyond 60–90 minutes, especially in heat. Losses accumulate to meaningful quantities here, and drinking large volumes of plain water starts diluting blood sodium. Hyponatraemia is documented in long endurance events, and the leading risk factor is not the heat but excessive plain water intake.

Vomiting and diarrhoea. The least disputable indication of all. Sodium and potassium losses are fast and large while absorption is impaired. WHO oral rehydration solutions have saved more lives than most drugs, and they work through sodium-glucose co-transport: glucose literally drags sodium and water across the intestinal wall.

Keto and the first weeks of a low-carbohydrate diet. Falling insulin reduces renal sodium reabsorption, and the body sheds sodium and water. Weakness, headache and dizziness on standing are the classic picture, and an extra 1–2 g of salt a day usually settles it.

Hot work and saunas. Builders, chefs and foundry workers lose several litres of sweat per shift.

Certain drugs and conditions. Diuretics, adrenal insufficiency, cystic fibrosis (where sweat is abnormally salty).

Situation	Electrolytes needed?	What exactly
An hour in the gym	No	Water, ordinary food afterwards
Two-hour run in the heat	Yes	Sports drink, 500–700 ml/h, 300–600 mg sodium
Gastrointestinal infection	Yes, essential	Pharmacy oral rehydration solution
Hangover	Probably not	Water and food; powder does not treat it
First weeks of keto	Yes	An extra 1–2 g of salt, potassium from food
Office day	No	Normal eating covers the requirement
Two or three sauna rounds	Usually not	Water; salty food afterwards if you sweat heavily

About cramps#

Exercise cramps are the electrolyte industry's central argument, and it is half out of date. The classic hypothesis blames sodium depletion and dehydration. It holds for a subset: athletes with heavy salty sweat during long events, where sodium genuinely resolves the cramps.

But the current review of mechanisms points to a second, more common pathway: altered neuromuscular control under fatigue — alpha motor neuron hyperexcitability caused by an imbalance between muscle spindle and Golgi tendon organ signalling. That mechanism has nothing to do with electrolytes at all, and it explains why cramps strike people with entirely normal bloodwork and why they arrive at the end of a session rather than in the middle.

Practical reading: if cramps come during long efforts in heat and you are a salty sweater, try sodium. If they show up at the end of an ordinary session or at night, the cause is more likely fatigue, muscle extensibility and training load — and magnesium is unlikely to touch it.

Читайте также: Magnesium: Forms, Doses and What It Actually Helps

What to buy, if anything#

A standard sports drink carries 400–600 mg of sodium and 30–60 g of carbohydrate per litre — a formulation aimed squarely at prolonged work. Sugar-free electrolyte powders supply sodium and potassium, but without glucose absorption is slower.

A home alternative for training: one litre of water, half a teaspoon of salt (about 1 g of sodium), 2–3 tablespoons of sugar or honey, the juice of half a lemon. Compositionally that is close to a commercial sports drink at a fraction of the price.

Pharmacy oral rehydration solution is its own category: its composition is calibrated for diarrhoeal losses, and a sports drink is not an adequate substitute during a gastrointestinal infection.

The bottom line#

Electrolytes are not an energy supplement but minerals whose concentration the body already defends fiercely. A healthy person on a mixed diet gets enough from food, and a morning powder in water improves nothing.

The genuine indications are narrow and easy to recognise: efforts beyond an hour or ninety minutes, especially in heat; vomiting and diarrhoea; the first weeks of a low-carbohydrate diet; a job or hobby that produces heavy sweating. In every other case the most useful electrolyte work is not buying a powder but adding vegetables and pulses for the potassium that nearly everyone is genuinely short of.

Читайте также: How Much Water Per Day: The Real Numbers and the Myths