Electrolyte drinks: when to use them and how to choose

An electrolyte drink provides water and minerals such as sodium, which is lost through sweat. It can be useful during a long race or a hot training session that causes heavy sweating. For a short, moderate run, however, water is usually enough.

The choice depends on exercise duration, environmental conditions and how much you sweat. Some drinks also contain carbohydrates, which provide energy during prolonged exercise; others have very few calories. Not all have the same composition or serve the same purpose.

What electrolytes are and why runners need them

Electrolytes are substances that carry an electrical charge when dissolved in body fluids. They include sodium, chloride, potassium, calcium and magnesium. They play a part in fluid balance, nerve signalling and muscle function.

The body regulates their concentrations through mechanisms involving, among other organs, the kidneys. A varied diet usually supplies these minerals, so an electrolyte label does not in itself make a drink necessary for everyday use.

When you run, evaporating sweat helps release heat. Sweat contains water and salts, mainly sodium and chloride. The amount lost differs between runners and also varies with intensity, temperature, humidity, clothing and adaptation to heat.

White marks on clothing after sweat has dried may indicate the presence of salt, but they cannot show precisely how much sodium has been lost. Nor is the colour of a shirt or the feeling that you have sweated heavily enough to establish an exact dose.

When an electrolyte drink makes sense

On an easy run of around 30 to 60 minutes in moderate temperatures, a special drink is generally unnecessary. Water during or after the session and regular meals are usually enough. Duration is a guide, not a dividing line beyond which everyone needs salts.

These drinks become more useful as exercise goes on, particularly beyond an hour, or when sweat losses are substantial. A long run on a humid morning along the Valencian coast, for example, may call for a different plan from a short jog on a cool day.

In those circumstances, a sports drink provides a way to carry fluid and sodium in the same container. If it also contains carbohydrates, it can contribute energy. That does not mean all fuel has to come from the bottle: gels and other foods also provide energy and need to be counted.

After training, water alongside a meal or snack containing salt is often a reasonable alternative. Replacing losses over the following hours is particularly important after a long session or when there is little time before the next workout.

Understanding sodium on the label

When assessing a drink intended to replace sweat losses, sodium content is more useful than the total number of minerals advertised. Potassium, calcium and magnesium have important roles, but adding large amounts does not automatically improve hydration.

Spanish and European labels generally list salt rather than sodium. As a conversion rule, 1 g of salt is approximately 400 mg of sodium. If a drink lists 0.1 g of salt per 100 ml, one litre provides about 400 mg of sodium; a 500 ml bottle provides approximately half that amount.

Compare amounts over the same volume. A tablet listing 300 mg of sodium per serving may be mixed with half a litre or a litre, depending on the instructions: the total remains the same, but the concentration changes. Following the stated dilution prevents different mixtures being treated as equivalent.

Products also come as powders, sachets and ready-to-drink bottles. Convenience varies, but what matters is what the amount actually consumed provides. Some formulations contain caffeine or other ingredients that are not essential for replacing fluid and may not suit certain people.

Carbohydrates: fuel, not just flavour

During prolonged running, carbohydrates help sustain the effort. A common guideline for endurance exercise lasting between one and two and a half hours is approximately 30 to 60 g per hour, although digestive tolerance and needs vary. Shorter efforts do not always require that amount.

A drink can provide part of this intake. For example, 500 ml of a mixture containing 6 g of carbohydrate per 100 ml supplies 30 g. If you also take a gel, its carbohydrates add to those in the drink; counting both gives a clearer total and helps avoid an unexpected digestive load.

A sugar-free electrolyte tablet may provide sodium, but it does not replace a source of energy. Conversely, a sweet drink may supply carbohydrates while containing little sodium. Nor is it necessary to avoid sugar automatically: during a long effort it serves a different purpose from sugar in a drink consumed out of habit away from training.

Isotonic, hypotonic and hypertonic drinks differ in their concentration of dissolved particles relative to body fluids. That classification does not by itself show how much sodium or energy they provide. When comparing specific options, the composition per 100 ml and the amount you expect to drink are more practical measures.

How much to drink on a run

Thirst is a useful signal, although on long efforts access to water and the ability to drink comfortably also matter. A common starting range is 400 to 800 ml per hour, adjusted to conditions and tolerance. It is not a mandatory target: a smaller person in cool weather may need less, while someone sweating heavily may need more.

One simple way to estimate losses is to weigh yourself without wet clothing before and after a session, record what you drink and account for any urine. As an approximation, each kilogram of weight lost represents close to one litre of fluid deficit; to estimate total sweat loss, add the fluid consumed and subtract urine produced.

For example, if you weigh 0.5 kg less afterwards, have drunk 500 ml and have not urinated, estimated sweat loss for that session is one litre. The figure describes that particular workout; it does not reveal sweat sodium concentration or establish a universal drinking amount.

Drinking much more than you lose also carries risks. Excess fluid can dilute sodium in the blood and cause exercise-associated hyponatraemia. Drinks containing salts do not remove that danger if consumed in excess. Confusion, a severe headache, vomiting or fainting during or after a race requires urgent medical attention.

How to make an electrolyte drink at home

A homemade mixture lets you control the ingredients. For one simple example, dissolve 1 g of table salt and 40 g of sugar in water, add a little lemon juice for flavour and top up with water to make one litre. Stir until dissolved. The salt supplies approximately 400 mg of sodium in the full litre.

Drinking 500 ml of this mixture provides approximately 200 mg of sodium and 20 g of sugar, plus the small and variable amount supplied by the juice. Weighing the salt is more reliable than using a pinch or a teaspoon, because their weight changes according to how they are filled.

This recipe is an option for exercise, not a medical oral rehydration solution. Keep it in a clean, closed container, refrigerate it and preferably consume it within 24 hours. Its composition can vary with the juice, and it does not allow every mineral present to be measured precisely.

Coconut water, juice and milk: what they offer

Coconut water contains potassium and fluid, but its sodium content is usually lower than that of a sports drink formulated to replace sweat losses. Amounts vary by product. It is therefore not necessarily equivalent to a sports mixture during several hours of running in hot conditions.

Fruit juices also provide water, carbohydrates and potassium. However, their sugar concentration may be high for some people during exercise and, on their own, they usually provide little sodium. Dilution changes both the flavour and the amount of carbohydrate per volume.

Milk provides fluid, protein and minerals, including calcium and potassium. It can be part of a post-training meal for those who tolerate it, although it is not essential or always comfortable to consume while running. Plant-based drinks have different compositions, especially in protein and minerals, so they should not be treated as equivalent without checking the label.

Cramps, illness and warning signs

A cramp during a run does not by itself prove an electrolyte deficiency. It can occur in connection with fatigue and other factors, and taking more salts does not guarantee it will go away. Heat can also cause serious problems even when someone is drinking: reducing exposure and finding a cool place matter too.

For diarrhoea or vomiting, a sports drink is not equivalent to a pharmacy oral rehydration solution formulated for those losses. If fluids cannot be kept down, there are signs of significant dehydration or symptoms are severe, medical assessment is needed. Confusion, fainting or a very high body temperature requires urgent attention.

People with kidney or heart disease, those following a sodium-restricted diet and those taking medicines that affect fluid or mineral balance should consult a healthcare professional before regularly using concentrated preparations. More minerals do not mean greater safety, especially when a medical condition is involved.

Hydration depends on context

The same drink may be practical on a long run and offer little benefit during a short session. The difference lies in fluid losses, exercise duration and energy needs, not in a package promising superior hydration.

For runners, an informed choice combines volume, sodium and carbohydrates with a straightforward assessment of the actual conditions. Water, everyday foods and sports drinks each have a different place: none needs to become the only answer for every run.