Hydration and Electrolytes: More Than Just Drinking Water

Water: The Underestimated Foundation

The human body consists of approximately 60% water. In the brain, this proportion is even around 75%. Water is involved in nearly every physiological process. It regulates body temperature, transports nutrients to cells, cushions joints and supports the excretion of metabolic waste through the kidneys (Popkin et al., 2010).

A fluid loss of just 2% of body weight can measurably impair cognitive performance and physical endurance. At 3 to 4% loss, aerobic capacity drops significantly. This is particularly relevant because many people do not consciously perceive mild dehydration.

The 2-Litre Rule: Myth or Guideline?

The widespread recommendation to drink 2 litres of water per day has no solid scientific basis. It likely traces back to a recommendation by the US Food and Nutrition Board from 1945, which also noted that a large portion of this amount is already consumed through food (Valtin, 2002).

Actual fluid requirements depend on many individual factors:

• Body weight and composition: A larger body requires more fluid.
• Physical activity: Athletes lose 0.5 to 2 litres of sweat per hour depending on intensity and ambient temperature.
• Climate and altitude: Heat, low humidity and high altitude increase requirements.
• Diet: Those who eat plenty of fruit, vegetables and soups take in more fluid through food.
• Health status: Fever, diarrhoea or vomiting increase requirements considerably.

A practical indicator is urine colour. Pale yellow suggests good hydration. Dark yellow signals that more fluid is needed.

What Are Electrolytes?

Electrolytes are minerals that carry electrical charges in the body. They are essential for the function of nerves, muscles and fluid balance. The four most important electrolytes in the context of hydration are:

Sodium

Sodium is the most important electrolyte in the extracellular space. It regulates fluid volume, blood pressure and nerve signal transmission. Sodium is lost in significant amounts through sweat. The concentration in sweat varies widely between individuals, ranging from 200 to 1600 mg per litre (Baker et al., 2016).

Potassium

Potassium is the counterpart to sodium and acts primarily within the cells. It is essential for muscle contraction and heart function. Good sources include bananas, potatoes, avocados and legumes.

Magnesium

Magnesium is involved in over 300 enzymatic reactions in the body. It plays a role in muscle relaxation, protein synthesis and energy production. A magnesium deficiency can lead to muscle cramps, fatigue and reduced performance.

Calcium

Calcium is not only important for bone health. It also plays a central role in muscle contraction and blood clotting. Small amounts of calcium are lost through sweat during heavy sweating.

Hyponatraemia: When Too Much Water Becomes Dangerous

Most people think of hydration only in terms of “drink more”. However, excessive water intake without adequate electrolyte replenishment can become dangerous. Hyponatraemia refers to a condition in which blood sodium concentration falls below 135 mmol/l.

This condition typically occurs when endurance athletes drink large quantities of plain water over several hours without replacing the sodium lost through sweat. Symptoms range from nausea and headaches to confusion and, in severe cases, life-threatening conditions.

Studies at the Boston and London Marathons found mild forms of hyponatraemia in up to 13% of finishers (Almond et al., 2005). Slower runners are particularly affected, as they spend many hours on the course and consume large amounts of water at every aid station.

Exercise and Sweat Loss

During exercise, the body loses not only water but also electrolytes. The composition of sweat varies considerably between individuals. Some people are “salty sweaters” and lose significantly more sodium than others.

When is water alone sufficient?

• During moderate activity under 60 minutes
• In cool temperatures with low sweat loss
• When a balanced meal is eaten before and after exercise

When are electrolytes beneficial?

• During intense activity lasting over 60 to 90 minutes
• In high temperatures or high humidity
• During heavy sweating (recognisable by salt crusts on clothing)
• During multi-hour endurance activities such as marathons or cycling races

The American College of Sports Medicine recommends in its Position Stand on fluid replacement that athletes should know their individual sweat rate and adjust fluid and electrolyte intake accordingly (Sawka et al., 2007).

Natural Electrolyte Sources

Commercial sports drinks are not strictly necessary to support electrolyte balance. Many natural foods provide relevant amounts:

• Coconut water: Contains potassium, magnesium and small amounts of sodium. A natural isotonic alternative, though relatively low in sodium for heavy sweaters.
• Banana: Rich in potassium (approximately 400 mg per piece) and provides quickly available carbohydrates.
• Salt: A pinch of sea salt in water provides sodium and trace minerals. A simple and effective solution for intense training.
• Vegetable broth: Provides sodium, potassium and magnesium. Particularly suitable for recovery after long sessions.
• Watermelon: High water content plus potassium and magnesium. An ideal snack on hot days.
• Potatoes and sweet potatoes: Rich in potassium and simultaneously good carbohydrate sources for recovery.

Commercial Sports Drinks: Useful or Marketing?

Commercial sports drinks such as Isostar or Gatorade typically contain water, sugar, sodium and potassium. For endurance athletes during intense exercise lasting over 60 to 90 minutes, they can be a practical solution (Shirreffs, 2003).

For everyday life or moderate training, they are generally unnecessary. Many commercial products also contain large amounts of added sugar, artificial colourings and flavourings. A homemade alternative made from water, a pinch of salt, some lemon juice and optionally honey can serve the same purpose.

Composition of a simple electrolyte solution:

• 500 ml water
• 1/4 teaspoon salt (approximately 500 mg sodium)
• 2 tablespoons lemon juice
• Optional: 1 teaspoon honey for flavour and carbohydrates

Practical Recommendations

Hydration does not need to be complicated. A few simple principles cover most situations:

• Listen to thirst. The thirst sensation is a reliable indicator in healthy individuals. There is no need to drink before feeling thirsty.
• Monitor urine colour. Pale yellow is the goal. Colourless suggests excessive drinking.
• Add electrolytes for prolonged exercise. From 60 to 90 minutes of intense activity, adding sodium is worthwhile.
• Do not overdo it. More water is not automatically better. Excessive drinking dilutes electrolyte concentration.
• Do not forget meals. A balanced diet with vegetables, fruit, nuts and salt already provides many electrolytes.

Hydration is an interplay of water and electrolytes. Those who only think about how much they drink and forget the minerals have only understood half the picture.

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Sources:

• Popkin BM, D’Anci KE, Rosenberg IH (2010). Water, hydration, and health. Nutrition Reviews.
• Shirreffs SM (2003). Markers of hydration status. European Journal of Clinical Nutrition.
• Sawka MN et al. (2007). American College of Sports Medicine Position Stand: Exercise and Fluid Replacement. Medicine & Science in Sports & Exercise.
• Valtin H (2002). “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 × 8”? American Journal of Physiology.
• Baker LB et al. (2016). Body map of regional vs. whole body sweating rate and sweat electrolyte concentrations in men and women. Journal of Applied Physiology.
• Almond CS et al. (2005). Hyponatremia among runners in the Boston Marathon. New England Journal of Medicine.