Electrolytes and hydration: labels and context

By DanielUpdated 23 Oct 2026
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30 years in strength training & bodybuilding7 min read
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Electrolyte products vary in their ingredients, quantities and serving instructions. This guide covers the label details, cited hydration sources and authorised wording to check when comparing them.

The authorised claims, verbatim

The boxes above show the EU-authorised health claims for magnesium, potassium and carbohydrate-electrolyte solutions, in the exact wording of Commission Regulation (EU) No 432/2012 (consolidated text of 20 August 2025). We don’t combine, intensify or paraphrase any of them.

What the studies say, outcome by outcome

Sweat loss varies from person to person

A review of sweat-testing methods and variability in athletes (Baker, 2017) describes how sweating rate and sweat sodium concentration vary within and between individuals, with exercise intensity, environmental conditions, heat acclimation, aerobic capacity, body size, sex, age, diet and hydration status among the factors it lists. The author reports that the simplest and most accurate method to assess whole-body sweating rate is the change in body mass during exercise, and that sweat testing can be a useful tool to estimate an athlete’s sweating rate and sweat sodium loss to guide fluid and electrolyte replacement strategies, provided the data are collected, analysed and interpreted appropriately. The review also notes that unstandardised methods and challenging field conditions can produce inconsistent or inaccurate results.

What the American College of Sports Medicine position stand covers

The American College of Sports Medicine’s position stand on exercise and fluid replacement (Sawka et al., 2007) gives guidance on fluid replacement for people performing physical activity. It states that the goal of drinking during exercise is to prevent excessive dehydration, which it defines as more than 2% of body weight lost from a water deficit, and excessive changes in electrolyte balance. Because of the considerable variability in sweating rates and sweat electrolyte content between individuals, it recommends customised fluid-replacement programmes, and says that individual sweat rates can be estimated by measuring body weight before and after exercise. For after exercise, it says the goal is to replace any fluid and electrolyte deficit. The paper dates from 2007, so it is worth reading it alongside the more recent sweat-testing review above.

Hyponatraemia in marathon runners

Hyponatraemia means a low sodium concentration in the blood. A cohort study at the 2002 Boston Marathon (Almond et al., 2005) enrolled 766 runners, of whom 488 (64%) provided a usable blood sample at the finish line. Thirteen per cent of those runners had hyponatraemia, defined as a serum sodium concentration of 135 mmol/L or less, and 0.6% had critical hyponatraemia (120 mmol/L or less). In the multivariate analysis, hyponatraemia was associated with weight gain during the race (odds ratio 4.2, 95% confidence interval 2.2 to 8.2), with a racing time of more than 4 hours compared with under 3 hours 30 minutes (odds ratio 7.4, 95% confidence interval 2.9 to 23.1), and with extremes of body-mass index. Female sex, the composition of the fluids ingested and use of nonsteroidal anti-inflammatory drugs were not associated with it. This was a study of marathon runners at one event, so it does not tell us what happens in shorter sessions.

Amounts, as reported by official sources

These figures come from different bodies for different purposes, so they are not interchangeable.

  • Magnesium, from the NHS and EFSA: adults aged 19 to 64 need 300 mg a day (men) or 270 mg a day (women) according to the NHS, which says most people should be able to get all the magnesium they need from a varied, balanced diet. For the EU, the tolerable upper intake level for magnesium from supplements is 250 mg a day for adults and for children from 4 years of age. It applies to readily dissociable magnesium salts and compounds such as magnesium oxide in food supplements, water or added to foods, and does not include magnesium naturally present in foods and beverages (EFSA, 2025; SCF, 2001). The NHS gives a higher UK figure: it says taking 400 mg or less a day of magnesium from supplements is unlikely to cause harm, and that high doses of more than 400 mg for a short time can cause diarrhoea.
  • Potassium, from the NHS and EFSA: adults aged 19 to 64 need 3,500 mg a day, and the NHS says most people should be able to get all the potassium they need from their diet. EFSA concluded in 2005 that the available data were insufficient to establish an upper level for potassium, and its overview of upper intake levels (version of August 2025) still records no adequate data to derive one (EFSA, 2005; EFSA, 2025). EFSA noted that elderly people may be more vulnerable to adverse effects of potassium because of reduced kidney function or drugs that affect potassium balance. The NHS likewise says that older people may be more at risk because their kidneys may be less able to remove potassium from the blood, and should not take potassium supplements unless advised to by a doctor.
  • Salt, from the NHS: adults should eat no more than 6 g of salt (2.4 g of sodium) a day. The NHS says that having too much salt is linked to high blood pressure, and that the Department of Health and Social Care says sodium chloride should not be used in supplements.
  • EU label reference values: under Article 32 of Regulation (EU) No 1169/2011, a vitamin or mineral declaration on a food label is also expressed as a percentage of the reference intakes in Annex XIII, which gives 375 mg for magnesium and 2,000 mg for potassium. These are labelling figures, not the NHS amounts above, so the milligram amount on the label is the number to read.
  • Foods: the NHS lists spinach, nuts and wholemeal bread as examples of magnesium sources, and bananas, some vegetables, beans and pulses, nuts and seeds, fish and meat as examples of potassium sources.

If you have a health condition, take medication, or are pregnant or breastfeeding, speak to a healthcare professional before taking electrolyte or mineral supplements.

What we do not say

  • Anything beyond the authorised wording. The authorised magnesium, potassium and carbohydrate-electrolyte wordings shown above do not cover cramp prevention, recovery or inflammation, so we don’t say any of those things. Sodium is not among the claims we quote.
  • Session-length or heat thresholds for when to use an electrolyte drink. The sources above say that sweat losses and needs vary widely from person to person, and the method they describe is to measure your own sweating rate, so we don’t give a one-size-fits-all rule.

Sources

This page is part of the CapyFuel Evidence Library — see how we summarise the research and pick sources. Related pages: vitamin D, omega-3, our magnesium guide, rest and recovery and supplements for muscle gain. Looking for prices? Our live price pages track protein, creatine, pre-workout and EAA/BCAA products — electrolyte products are not one of the tracked categories. See the Malta and Cyprus Price Index, supplement prices in Malta and supplement prices in Cyprus.

Frequently asked questions

Which electrolyte claims are authorised in the EU?

The exact EU-authorised wording is shown in the box on this page.

How do sweat losses differ between people?

A review of sweat-testing research describes considerable variability in sweating rate and sweat sodium concentration within and between individuals (Baker, 2017). The American College of Sports Medicine position stand says individual sweat rates can be estimated by measuring body weight before and after exercise (Sawka et al., 2007).

What did the Boston Marathon study find about low blood sodium?

In a cohort of 488 runners with a usable finish-line blood sample, 13% had a serum sodium concentration of 135 mmol/L or less. In the multivariate analysis it was associated with weight gain during the race, a racing time of more than 4 hours and extremes of body-mass index, and not with female sex, the composition of the fluids ingested or use of nonsteroidal anti-inflammatory drugs (Almond et al., 2005).

What intakes of magnesium, potassium and salt does the NHS give?

The NHS gives 300 mg of magnesium a day for men and 270 mg for women aged 19 to 64, 3,500 mg of potassium a day for adults aged 19 to 64, and no more than 6 g of salt (2.4 g of sodium) a day for adults. These are NHS figures; the reference intakes used on EU food labels are different labelling figures.

Sources & further reading

  1. Baker 2017 — Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability (Sports Medicine, PMC)
  2. Sawka et al. 2007 — American College of Sports Medicine position stand: Exercise and fluid replacement (Med Sci Sports Exerc, PubMed)
  3. Almond et al. 2005 — Hyponatremia among runners in the Boston Marathon (N Engl J Med, PubMed)
  4. NHS — Others: vitamins and minerals (magnesium, potassium, sodium chloride)
  5. EFSA 2025 — Overview on Tolerable Upper Intake Levels as derived by the SCF and the EFSA NDA Panel (version 11, August 2025)
  6. SCF 2001 (magnesium) and EFSA 2005 (potassium) — Tolerable Upper Intake Levels for Vitamins and Minerals (EFSA, 2006)
  7. Regulation (EU) No 1169/2011 — food information to consumers, Art. 32 and Annex XIII (EUR-Lex, consolidated 1 Apr 2025)
  8. Commission Regulation (EU) No 432/2012 — authorised health claims, wording and conditions of use (EUR-Lex, consolidated 20 Aug 2025)
  9. EU Register of authorised nutrition and health claims made on foods