Electrolytes and hydration: when you actually need them

Electrolytes are among the body’s most important micronutrients, involved in all the major physiological processes — from muscle contraction to blood pressure regulation. Even so, many athletes and health-conscious people ask: is an electrolyte supplement truly necessary, or is it just a marketing trick? In this article, we look at the evidence: what electrolytes are, what they do and when extra intake is justified.

What are electrolytes and how do they work in the body?

Electrolytes are mineral salts that dissolve into ions in water and conduct an electrical charge. The main electrolytes in the body are sodium (Na⁺), potassium (K⁺), magnesium (Mg²⁺), calcium (Ca²⁺) and chloride (Cl⁻). For more detail, you can review the essential minerals and their roles in our separate overview.

The main functions of electrolytes:

• Fluid balance — sodium regulates the fluid between cells, potassium the fluid inside them. Their balance determines how well cells retain and release water.
• Muscle contraction — every muscle contraction requires the release of calcium and the exchange of sodium and potassium across the cell membrane (Sawka et al., 2007).
• Nerve transmission — action potentials, the signals between nerve cells, depend directly on the movement of ions across the membrane.
• Acid-base balance — keeping blood pH within a narrow range (7.35–7.45) depends in part on the balance of bicarbonate and chloride.

When are extra electrolytes truly necessary?

The most common misconception is that an electrolyte supplement is necessary for every active person. The reality is more complicated.

Under normal circumstances, food and water are enough. Healthy, balanced eating covers most people’s daily electrolyte needs. We get sodium from salty foods, potassium from fruit and vegetables, and magnesium from nuts and whole grain products. If you want to assess your overall micronutrient intake, our overview of required vitamin amounts is also useful.

Extra electrolytes are justified in the following cases:

1. Prolonged intense training (over 60–90 minutes). Through sweat, the body loses on average 0.5–2 liters of water and 200–1000 mg of sodium per hour (Sawka et al., 2007). If training lasts over an hour and you sweat heavily, drinking only water can put you at risk of hyponatremia — a condition in which the sodium level in the blood drops too low.
2. Exposure to heat. In conditions of high outdoor temperature and humidity, sweating is more intense and electrolyte loss is faster.
3. Recovery from illness. Vomiting and diarrhea remove significant amounts of sodium, potassium and chloride from the body. The World Health Organization (WHO) recommends an oral rehydration solution in such cases, containing both water and electrolytes — you can find more detailed guidance in the WHO ORS guide.
4. On a keto diet or strict calorie restriction. Drastically cutting carbohydrates depletes glycogen stores, which is accompanied by greater sodium loss through the kidneys.

Isn’t water enough? Electrolytes vs. plain water

For short workouts (under 60 minutes) at moderate intensity, plain water is usually completely sufficient. In a study, Shirreffs and Maughan (1998) showed that the body restores lost fluid more effectively when the drink contains sodium — but this applies primarily in cases of significant dehydration (over 2% of body weight).

Another problem is that many commercial sports drinks contain large amounts of sugar, which does make up for the energy lost during prolonged endurance training but isn’t necessary for a shorter workout. If you’re weighing up supplements more generally, it’s also worth reading 💊 Do you need supplements? When to actually use them — it helps build a complete picture of the role of supplements.

A practical rule:
– Workout under 60 min, moderate sweating → water
– Workout of 60–90 min, heavy sweating → water + some salty food or a diluted sports drink
– Workout over 90 min, hot weather or competition conditions → adding electrolytes is justified

How does an electrolyte deficiency show up?

Electrolyte imbalances can show up as a range of symptoms, from mild to serious:

• Sodium deficiency (hyponatremia): headache, nausea, confusion, and in more severe cases seizures
• Potassium deficiency (hypokalemia): muscle weakness, fatigue, heart palpitations
• Magnesium deficiency: muscle cramps, irritability, sleep disturbances (Maughan, 2003)
• Calcium deficiency: numbness, muscle spasms, and weakening teeth and bones in the longer term

It’s important to remember that an electrolyte deficiency is diagnosed with a blood test — you can’t draw accurate conclusions from how you feel. If in doubt, see a doctor.

How do you adjust electrolyte intake to your training plan?

Your electrolyte needs depend strongly on the type, duration and intensity of your training. If you already have a structured training program, it’s worth building your hydration strategy around the training loads planned in it. Endurance athletes who do long outdoor sessions in summer need to pay considerably more attention to electrolytes than someone doing a gym workout three times a week.

Practical tips:
– Drink regularly throughout the day, not just during training
– The taste of your sweat can tell you how much sodium you are losing — saltier sweat means greater losses
– Recovery after training speeds up if you eat electrolyte-rich foods (bananas, nuts, dairy products) within 30–60 minutes
– Smarter habits help you avoid overheating: stay in the shade and drink before you get thirsty

References

• Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. (2007). American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine & Science in Sports & Exercise. 39(2):377-390. PMID: 17277604
• Shirreffs SM, Maughan RJ. (1998). Volume repletion after exercise-induced volume depletion in humans: replacement of water and sodium losses. American Journal of Physiology. 274(5 Pt 2):F868-75. PMID: 9612330
• Maughan RJ. (2003). Impact of mild dehydration on wellness and on exercise performance. European Journal of Clinical Nutrition. 57 Suppl 2:S19-23. PMID: 14681719
• World Health Organization. (2006). Oral Rehydration Salts: Production of the new ORS. WHO/FCH/CAH/06.1. Geneva: WHO Press.

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