Electrolyte Science: How Minerals Support Recovery

Whether you're recovering from a night out or a long run, someone will tell you that you "need electrolytes". Here's what that actually means — and when it's true.

Electrolytes are real, important and widely misunderstood. They get credited with fixing hangovers (they don't), blamed for every cramp (sometimes fairly) and sold in every colour of sports drink. The science underneath is more interesting than the marketing, and a lot more honest.

Your body is roughly 60% water. That water doesn't float about freely; it's held in the right compartments by electrolytes — electrically charged minerals you can't make yourself and have to eat or drink. You do lose them: through urine, through sweat, and occasionally through the less dignified routes of a bad night. How much you lose, and whether it matters, depends a lot on what you were doing.

This guide covers what electrolytes do, what alcohol and exercise really do to them (less than you've been told in one case, more in the other), why sodium is the one that makes water stay put, and how to replace what you've lost without falling for the hype.

What are electrolytes?

Electrolytes are minerals that carry an electrical charge when dissolved in water. Sodium, potassium, magnesium, calcium, chloride, phosphate and bicarbonate are the main ones your body relies on. Each has a specific job, and they work as a system.

In your body, electrolytes do four critical things:

• Regulate fluid balance. Electrolytes determine where water sits — inside cells, around them, or in your bloodstream. Sodium is the main one holding water in your blood and the fluid around your cells; potassium does the same job inside them.
• Enable nerve signalling. Every thought, movement and reflex depends on electrical signals passing between nerve cells. Those signals are generated by sodium and potassium moving across cell membranes.
• Drive muscle contraction. Whether it's your heart beating or your legs running, calcium, sodium, potassium and magnesium let muscles contract and relax.
• Help regulate pH. Bicarbonate and other electrolytes keep your blood within a narrow acidity range.

Serious electrolyte disturbance is a medical problem — the kind that happens with prolonged vomiting and diarrhoea, certain medicines or kidney disease, not after a Friday night. The everyday version is subtler: you're a little short of fluid and salt, you haven't eaten properly, and you feel it.

The electrolytes that matter for recovery

Sodium: the one that makes water stay

Sodium is the most abundant electrolyte outside your cells and the main thing that sets the concentration of your blood. That's why it matters more than any other electrolyte for rehydration: when you drink fluid with sodium in it, your kidneys hold on to more of the water.

This has been measured directly. In a classic Aberdeen study, volunteers who had sweated out about 2% of their body weight drank one-and-a-half times what they'd lost as drinks containing 2, 26, 52 or 100 mmol/L of sodium. About six hours later, the people on the near-sodium-free drink were still almost 700 ml down; the ones on the 52 and 100 mmol/L drinks were back in balance. The fraction of fluid retained rose in step with the drink's sodium content (Maughan & Leiper, 1995). A follow-up showed that volume matters too: you need to drink more than you lost, but without enough sodium the surplus mostly becomes urine (Shirreffs et al., 1996).

How much you need: the NHS advice for adults is no more than 6 g of salt a day (about 2.4 g of sodium) — most of us already get more than that from food. You'll find sodium in table and sea salt, bread, cheese, cured meats, soy sauce, stock, olives and most processed food. People who sweat heavily during long exercise may need to replace more on those days.

Potassium: the inside partner

Potassium is the main electrolyte inside your cells, balancing sodium outside. Together they create the electrical gradient that powers nerve signals and muscle contractions, and your heart rhythm depends on potassium staying within a tight range. Adults need about 3,500 mg a day according to the NHS, and the only sensible way to get that is food.

Bananas get the credit, but potatoes, avocados, spinach and other leafy greens, beans and lentils, yoghurt and fish are all rich sources. Most rehydration drinks and sachets, Humans Against included, contain only a small amount of potassium relative to a day's intake — useful as part of a drink, not a substitute for lunch.

Magnesium: the one alcohol actually affects

Magnesium is a cofactor in more than 300 enzyme reactions, including the ones that turn food into usable energy, and it's the electrolyte with the clearest link to drinking. In 1963, researchers gave ethanol to both healthy volunteers and heavy drinkers and measured a prompt rise in urinary magnesium excretion in both groups (Kalbfleisch et al., 1963). A smaller Swedish study found that even moderate drinkers excreted more magnesium and calcium in their urine after a magnesium load than non-drinkers did, in proportion to how much they drank (Rylander et al., 2001). One night out won't make you deficient, but alcohol does nudge magnesium out of the body, and sustained heavy drinking is a well-recognised cause of low magnesium (Shane & Flink, 1991).

The NHS puts the daily requirement at 300 mg for men and 270 mg for women (aged 19 to 64), and says a varied diet should cover it: pumpkin seeds, almonds, spinach, wholegrains, beans and dark chocolate are all good sources. Magnesium's authorised claims are also the ones most relevant to the morning after: it contributes to electrolyte balance, to normal muscle function, to normal functioning of the nervous system, and to the reduction of tiredness and fatigue. Each Humans Against sachet contains 200 mg of magnesium (53% of the NRV).

Calcium: important, but not a recovery electrolyte

Calcium is an electrolyte too, essential for muscle contraction, nerve-to-muscle signalling and bone. But the amounts lost in sweat and urine after a night out or a workout are small, and dairy, fortified plant milks, tinned fish with bones and leafy greens cover it comfortably. Calcium isn't one of the electrolytes in Humans Against, and it doesn't need to be — this is one for your diet, not your recovery drink.

What alcohol actually does to your electrolytes

The popular story is that alcohol switches off your kidneys' water-saving hormone, you urinate out litres of fluid and electrolytes, and that's your hangover. The mechanism is real; the scale is not what the story suggests.

The mechanism: alcohol suppresses antidiuretic hormone (vasopressin), which normally tells your kidneys to conserve water. Less vasopressin, more urine. That part is settled physiology.

The scale: a diet-controlled crossover trial gave older men a moderate dose of alcohol — 30 g, roughly three to four UK units — as beer, wine or spirits, matched against alcohol-free beer, alcohol-free wine and water. Wine and spirits produced a small, short-lived increase in urine output over the first four hours; by 24 hours there was no difference at all. Beer was no different from alcohol-free beer at any time point, and urine sodium and potassium followed the same pattern (Polhuis et al., 2017). In other words, moderate drinking makes you wee a bit more for a few hours, and your body corrects for it within the day.

The hangover link: when researchers have actually measured blood and urine the morning after, electrolyte concentrations and markers of dehydration (including vasopressin) did not track with how bad people's hangovers were. The strongest correlates were immune-system factors (Penning et al., 2010). So electrolyte loss isn't the engine of a hangover — which is why rehydration fixes thirst and a dry mouth but doesn't fix the headache. We've covered that honestly in Electrolytes vs water: what actually helps the next day.

What a heavy night does reliably do is three smaller things at once: a modest fluid-and-salt deficit from the extra urine, a measurable loss of magnesium, and a poor night's eating and sleeping. Vomiting changes the picture — you lose fluid, acid and chloride — and if you've been sick, a drink with some salt and sugar in it is a sensible way to rehydrate. (Vomiting that won't stop, or that comes with confusion or severe pain, is a reason to call NHS 111, not to reach for a sachet.)

Exercise and sweat: where the losses are real

Exercise is a different story, because sweat is where meaningful electrolyte loss actually happens.

Sweat is a dilute salt solution, and how salty it is varies enormously. A 2017 review of sweat-testing research put the normal range of sweat sodium at roughly 10 to 90 mmol/L — about 230 to 2,000 mg per litre — with a several-fold difference between individuals (Baker, 2017). What moves it:

• Genetics. Some people are simply "salty sweaters" — the white crust on a black T-shirt is the giveaway.
• Heat acclimatisation. Over a couple of weeks in the heat, your sweat glands get better at reabsorbing sodium, so your sweat becomes more dilute even as you sweat more.
• Intensity and conditions. Harder efforts in hotter weather mean higher sweat rates, and total loss is rate × concentration × time.

Put numbers on it: a heavy sweater producing 1.5 litres an hour at 1,000 mg/L loses about 1.5 g of sodium an hour — more than half the NHS daily salt guideline in sodium terms. Potassium and magnesium losses in sweat are much smaller, which is why sports hydration advice is almost entirely about sodium.

The plain-water problem during long exercise: drinking large volumes of plain water through a long event, while losing salty sweat, can dilute blood sodium — exercise-associated hyponatraemia. Among 488 finishers tested at the 2002 Boston Marathon, 13% had low blood sodium. The risk factors were drinking so much that runners actually gained weight during the race and being on the course for more than four hours; notably, the type of fluid (water or sports drink) made no difference (Almond et al., 2005). The protection is not a particular drink — it's not overdrinking. Drink to thirst.

Why sodium (and a little glucose) makes water count

Two pieces of physiology explain why a pinch of salt and a little sugar beat plain water for getting fluid back on board.

Osmolality. This is the concentration of dissolved particles in a fluid. Your blood sits at about 285 to 295 mOsm/kg and your body defends that number closely. Drink a lot of plain water quickly and your blood gets slightly more dilute; your kidneys respond by making more, paler urine until the concentration is back where it should be. (Contrary to a common claim, this doesn't "dehydrate your cells" — dilute blood pushes a little water into cells, not out of them.) Fluid with sodium in it keeps your blood concentration steadier, so less of what you drank is sent straight back out — exactly what the Aberdeen trials measured.

Sodium-glucose co-transport. The cells lining your small intestine carry a transporter (SGLT1) that pulls in a sodium ion and a glucose molecule together, and water follows the solute osmotically. Pairing sodium with a modest amount of glucose therefore speeds up how quickly fluid crosses the gut wall. This is the discovery behind oral rehydration solution, which has been used for decades to treat dehydration from diarrhoeal illness (Ofei & Fuchs, 2019; Singh et al., 2014).

The WHO's current reduced-osmolarity ORS is the reference recipe. Per litre of water it contains 2.6 g sodium chloride, 13.5 g glucose, 1.5 g potassium chloride and 2.9 g trisodium citrate, giving sodium 75, chloride 65, glucose 75, potassium 20 and citrate 10 mmol/L at a total of 245 mOsm/L (WHO, 2006). That's a medical formulation for people losing litres to diarrhoea; it's also the clearest illustration of the principle. Plain water can't trigger the co-transport mechanism because it contains neither half of the pair.

How to replenish electrolytes sensibly

Option 1: Food

For almost everyone, almost all the time, food is how electrolytes are replaced. Breakfast with something salty, a banana or some yoghurt, a handful of nuts: that covers sodium, potassium and magnesium together, with the fibre and protein the morning after also needs. It isn't fast, but it is complete. If you can eat, eat — we've laid out the morning-after routine that makes it easiest.

Option 2: Drinks

Sports drinks typically run at 4–8% carbohydrate because they're built to fuel exercise lasting over an hour, with sodium added. During a long session they do that job well. The morning after a night out, that's a lot of sugar for a problem that isn't about fuel — see our low-sugar hangover recovery guide.

Oral rehydration salts from the pharmacy are the WHO-style formulation above: salty, lightly sweet and designed for illness. If you've been vomiting or have a stomach bug, they're the right tool, and the pharmacist can advise.

Electrolyte sachets and tablets sit between the two: less sugar than a sports drink, less sodium than medical ORS, usually with magnesium and vitamins added. The useful question for any of them is what's actually in the sachet.

Option 3: What's in a Humans Against sachet

We'd rather show you the numbers than use the word "optimised". The electrolyte-relevant contents of one 9 g sachet, mixed into 200 ml of cold water, are:

That's a sodium-and-glucose pairing on the ORS principle at a far gentler salt level than a medical sachet, a meaningful dose of magnesium, and the vitamins that carry the energy and tiredness claims — alongside the other actives that make up the 24 ingredients. It is not a medical ORS and we don't pretend it is. Each sachet also contains 100 mg of caffeine, about the same as a cup of coffee; the maximum recommended intake is 400 mg a day from all sources.

How to take it

Follow the pack: empty one or two sachets into a glass, add 200 ml of cold water, stir until dissolved and drink within an hour of mixing. No more than two sachets a day. Sip it rather than downing it — steady intake is kinder on a delicate stomach — and have food alongside when you can. Humans Against is not suitable for under-18s or for women who are pregnant or breastfeeding, and if you have a medical condition or take prescribed medication, check with your doctor before use. After exercise, remember the Aberdeen finding: you need to drink a bit more than you lost, over the following hours, for the fluid to stick.