Electrolytes and Hydration: What Active People Should Know

Every training session costs water, and sweat also carries minerals out of the body. This guide explains how much fluid people generally need, how to estimate your own sweat losses, what electrolytes are, and why drinking far more than you sweat can be a problem too.

Key points

  • EFSA's adequate intakes for total water, from drinks and food together, are 2.0 litres a day for women and 2.5 litres a day for men (EFSA NDA Panel, 2010).
  • Sweat rates and the amount of electrolytes lost in sweat vary considerably between people (Sawka et al., 2007).
  • A common goal during exercise is to avoid losing more than 2% of body weight through water loss, without drinking more than you lose.
  • Over-drinking can lower blood sodium, a condition called exercise-associated hyponatraemia.
  • Weighing yourself before and after training is a simple way to estimate your own sweat losses.

What are electrolytes?

Electrolytes are minerals that carry an electrical charge when dissolved in water, including sodium, potassium, chloride, magnesium and calcium. Sweat contains mostly sodium and chloride, with smaller amounts of potassium, magnesium and calcium.

In the EU, authorised health claims state that magnesium contributes to electrolyte balance and to normal muscle function, and that potassium contributes to normal muscle function and to normal functioning of the nervous system (Commission Regulation (EU) No 432/2012). These claims may only be made for foods that are at least a source of the mineral concerned.

How much fluid do you need each day?

EFSA set adequate intakes for total water of 2.0 litres a day for women and 2.5 litres a day for men. These figures cover water from all sources, including food (EFSA NDA Panel, 2010). Needs are higher in hot conditions and when you are physically active.

Two authorised EU claims relate to water: water contributes to the maintenance of normal physical and cognitive functions, and water contributes to the maintenance of normal regulation of the body's temperature. To obtain the claimed effect, at least 2.0 litres of water from all sources should be consumed per day.

How much do you lose when you train?

The American College of Sports Medicine (ACSM) position stand on exercise and fluid replacement stresses that sweating rates and the electrolyte content of sweat vary considerably between individuals, and therefore recommends customised fluid replacement plans (Sawka et al., 2007). How much you sweat also depends on how hard you train, the temperature and humidity, your clothing and how used you are to the heat. That is why general advice is a starting point, not a rule.

Estimate your own sweat loss

Individual sweat rates can be estimated by measuring body weight before and after exercise (Sawka et al., 2007):

  1. Weigh yourself before a typical training session, after using the toilet and in minimal clothing.
  2. Note how much you drink during the session.
  3. Towel off and weigh yourself again straight afterwards, in the same clothing.
  4. Weight lost plus fluid drunk gives an estimate of sweat loss. One kilogram of body weight corresponds to roughly one litre of fluid.

Repeat this in different seasons and at different intensities, because your losses change with the conditions.

Avoid both dehydration and over-drinking

According to the ACSM, the goal of drinking during exercise is to prevent excessive dehydration, defined as losing more than 2% of body weight through water loss, and excessive changes in electrolyte balance (Sawka et al., 2007). The National Athletic Trainers' Association recommends measuring sweat rates and developing individual fluid plans that promote sufficient, but not excessive, hydration before, during and after activity (McDermott et al., 2017).

Drinking more than you lose carries its own risk. The same position statement warns active people about over-drinking and hyponatraemia, an abnormally low blood sodium level (McDermott et al., 2017), and an international consensus statement is dedicated to exercise-associated hyponatraemia (Hew-Butler et al., 2015). Gaining weight over a training session is a sign that you drank more than you lost.

After training

After exercise, the goal is to replace any fluid and electrolyte deficit; how quickly you need to do this depends on when you train next (Sawka et al., 2007). With plenty of time before the next session, regular meals and drinks are usually enough. With a short turnaround, plan your fluid and salt intake more deliberately.

Sports drinks and electrolyte powders

In the EU, two claims are authorised for carbohydrate-electrolyte solutions: they contribute to the maintenance of endurance performance during prolonged endurance exercise, and they enhance the absorption of water during physical exercise. These claims may only be used for drinks that meet strict criteria: 80–350 kcal per litre from carbohydrates, at least 75% of the energy from carbohydrates that cause a high glycaemic response (such as glucose, glucose polymers and sucrose), 20–50 mmol/L (460–1,150 mg/L) of sodium, and an osmolality of 200–330 mOsm/kg water (Commission Regulation (EU) No 432/2012). Products that do not meet these criteria, for example sugar-free mineral powders, cannot carry these claims.

If you use an electrolyte product, compare the amounts of sodium, potassium and magnesium per serving with your own needs, and follow the directions on the label. For example, Genetic Nutrition Laboratories Base Powder Electrolyte is a powdered mineral blend with minerals in citrate form; its product page lists the composition per serving and the directions.

Who should take extra care?

If you have high blood pressure, a heart or kidney condition, follow a low-sodium diet or take medication that affects fluid or electrolyte balance, ask a doctor before changing your fluid or salt intake or using electrolyte products.

A practical checklist

  • Spread drinks across the day and include water-rich foods.
  • Start long or hot sessions well hydrated.
  • Use your own sweat-loss estimate as a guide during training, and avoid gaining weight over a session.
  • After training, replace what you lost; plan more carefully when the next session is soon.
  • Check the label of any electrolyte product for the amounts per serving.

Hydration is one part of recovery. Read our guides to recovery fundamentals and understanding creatine.

References

  1. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on Dietary Reference Values for water. EFSA Journal. 2010;8(3):1459. doi:10.2903/j.efsa.2010.1459
  2. Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods (consolidated version). EUR-Lex
  3. Sawka MN, Burke LM, Eichner ER, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377–390. doi:10.1249/mss.0b013e31802ca597
  4. McDermott BP, Anderson SA, Armstrong LE, et al. National Athletic Trainers' Association position statement: fluid replacement for the physically active. J Athl Train. 2017;52(9):877–895. doi:10.4085/1062-6050-52.9.02
  5. Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clin J Sport Med. 2015;25(4):303–320. doi:10.1097/JSM.0000000000000221
  6. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on the substantiation of health claims related to carbohydrate-electrolyte solutions. EFSA Journal. 2011;9(6):2211. doi:10.2903/j.efsa.2011.2211

This article is general information and is not medical advice. If you have a medical condition, are pregnant or breastfeeding, or take medication, speak to a healthcare professional before changing your fluid intake or using food supplements.

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