Electrolytes explained: when you need an electrolyte drink, tablets or powder – and when water is enough

Electrolytes: what they are and when you need them

Electrolytes are minerals that carry an electrical charge in your blood: sodium, potassium, chloride and magnesium. They balance fluid, carry nerve signals and help muscles contract. Most people get enough from food, and plenty of sodium.

Replacing them separately makes sense when you lose them faster than you eat them:

• long endurance sessions – running, cycling, skiing or hiking for several hours;
• heavy sweating in the heat – training, outdoor work or a hot journey;
• diarrhoea or vomiting – which needs a specific solution, not a sports drink.

To turn sodium on a label into salt, multiply by 2.5: 400 mg of sodium is 1 g of salt.

Electrolyte drinks for sport: when water isn’t enough

The American College of Sports Medicine (ACSM) stresses that sweat rate and sweat sodium vary widely from person to person. So there’s no single formula. The aim is to avoid losing more than 2% of your body weight during exercise, because that level of dehydration can hurt performance.

How to work out what you lose:

• weigh yourself before and after an hour’s session, without clothes; each kilogram lost is roughly a litre of sweat;
• drink to thirst – the advice of the 2015 international consensus on hyponatraemia;
• if you weigh more after an event than before, you drank too much.

ACSM says that in certain situations a drink with electrolytes and carbohydrate has benefits over plain water. Long sessions and heavy sweating are the usual examples. The carbohydrate gives energy, and sodium helps you hold on to what you drink. For an hour in the gym, water is usually enough, and your next meal replaces the salt and potassium. Pick your situation:

Hyponatraemia: why “drink more” can be dangerous

Hyponatraemia means blood sodium below 135 mmol/L. In sport, the 2015 international consensus says the main cause is drinking too much, not too little salt. Your risk is higher if:

• you’re exercising for more than 4 hours at a slow pace;
• you drink at every station rather than to thirst, and gain weight during the event;
• you’re less experienced or less trained, or your BMI is very low or very high.

And one more thing: electrolyte drinks don’t prevent hyponatraemia if you overdrink them. They contain far less sodium than your blood does. Warning signs are nausea, headache, puffiness and confusion. Vomiting, seizures or confusion after a long event need emergency care, not another drink.

Your bathroom scales can show how much you sweat, and if you’re overdoing the water:

Electrolytes for diarrhoea and vomiting: oral rehydration salts

With a stomach bug you lose water, sodium and potassium in stools and vomit. WHO and UNICEF developed oral rehydration salts (ORS), sold in UK pharmacies as powder sachets. The WHO formula per litre of water:

• sodium – 75 mmol (about 1.7 g);
• glucose – 75 mmol (13.5 g);
• potassium – 20 mmol (about 0.8 g);
• chloride – 65 mmol and citrate – 10 mmol.

The glucose isn’t there for taste: in this ratio it helps your gut absorb sodium and water. According to WHO and UNICEF, the reduced-osmolarity solution cut the need for unplanned drips in children by a third compared with the old formula.

Mix it exactly as the pack says and sip slowly, especially if you feel sick. The NHS says not to give young children fruit juice or fizzy drinks, which can make diarrhoea or vomiting worse. Sports drinks and sugar-free tablets aren’t a substitute for ORS.

Get urgent advice from your GP or NHS 111 if you’re confused or very drowsy, dizzy when you stand up, passing very little urine, or breathing fast or have a racing heart. Babies, older people and anyone with a long-term condition need help sooner.

Sugar-free tablets vs powder vs sports drinks

On the label, check the Sodium, Potassium and Magnesium lines per serving. If your powder contains magnesium and you also take magnesium for sleep, add them up: EFSA advises no more than 250 mg a day from all supplements. Some “energy” electrolytes contain caffeine and taurine; our taurine guide explains the latter.

Potassium, magnesium and sodium: who should take care

• Kidney disease. NIH ODS notes that with chronic kidney disease potassium isn’t cleared well, so even intakes below the usual guide can push blood levels dangerously high. Magnesium from supplements is cleared by the kidneys too. Use electrolytes only if your kidney team agrees.
• Blood pressure and heart medicines. ACE inhibitors, ARBs (sartans) and potassium-sparing diuretics (spironolactone, amiloride) make you hold on to potassium. Avoid potassium tablets and powders unless your GP agrees.
• Salt substitutes are often potassium chloride: 440–2,800 mg of potassium per teaspoon. That counts too.
• Older people. Food Standards Scotland advises against potassium supplements without medical advice, because ageing kidneys clear potassium less well.
• High blood pressure and heart failure. Sodium from powders adds to the salt in your food. If you’ve been told to limit fluid or salt, don’t take electrolytes without your doctor’s agreement.

Before combining electrolytes with other supplements, check the pairs in our vitamin compatibility chart.

How to choose electrolytes on iHerb

1. Decide what it’s for: long sessions, heat or diarrhoea. For diarrhoea, choose oral rehydration salts.
2. For sessions over 2 hours, pick a powder with sodium and carbohydrate; for heat and travel, sugar-free tablets.
3. Check the sodium per serving and count it alongside the salt in your food.
4. Check the potassium and magnesium, especially if you take magnesium separately or use blood pressure medicines.
5. Skip products with caffeine if you train in the evening or are sensitive to it.
6. With kidney or heart disease or high blood pressure, talk to your GP first.

If you lift weights, the best-studied supplement is creatine monohydrate, and the core set for men is in our guide to supplements for men. Not sure where to start? Try our vitamin check.