The Science of Hydration - Sweat sodium concentration: why measure and what influences it?

October 8, 2020
The Science of Hydration - Sweat sodium concentration: why measure and what influences it?

Recently we launched the MX3 Sweat Sodium Test – a kit which contains everything needed to collect and analyse a sweat sample for sodium levels in combination with the MX3 LAB PRO. In this article we’ll discuss how sweat sodium concentration varies and what factors can influence this important parameter that informs individuals on electrolyte replacement needs.

Why measure sweat sodium concentration?

The main electrolytes lost in sweat are sodium, potassium, calcium, magnesium and chloride1. Of these, sodium and chloride make up the majority– up to several grams per litre of sweat. As a result of this, athletes or workers with a high sweat sodium concentration can easily exceed the recommended daily intake for salt, particularly when they are sweating heavily or over extended periods of time. Both insufficient and excessive sodium intake is unhealthy2, so it’s important to understand how much sodium is being lost and therefore needs to be replaced using a personalised electrolyte replacement strategy.

How much can sweat sodium concentration vary?

Sweat sodium concentration varies dramatically between individuals, from 250 mg/L to 3000 mg/L3. The MX3 Sweat Test Kit categorises sweat sodium concentration into four categories across this range; low, moderate high and very high sweat sodium concentration.

What factors can influence sweat sodium concentration?

There are many factors which can impact sweat sodium concentration including body mass and composition, gender, fitness levels, medication and genetics. Some of the major factors are:


Both sweat rate and sweat sodium concentration increase with higher intensity physical activity. Compared to low intensity exercise (45% VO2max) moderate intensity exercise (65% VO2max) can increase sweat sodium concentration more than 50%4. For this reason, it’s important to assess your sweat sodium levels at a work or exercise intensity that is typical of everyday activities.

Environmental Acclimatization

When working or exercising in hot or humid conditions, sweat rate will increase to help the body reduce core temperature by evaporative cooling. With repeated exposure to heat stress, the body begins to adapt as part of a process known as heat acclimatization. Individuals unacclimatized to work or exercise in high temperature environments typically have a higher sweat sodium concentration than those who have acclimatized. Sweat sodium concentration can decrease by up to 45% during a 1-2 week acclimatization period5.


A change in diet can also impact sweat sodium concentration, as the body looks to conserve or excrete excess sodium. Consuming a high sodium diet for only a few days will increase sweat sodium concentration by over 10%, and conversely consuming a low sodium diet will decrease sweat sodium concentration by a similar amount6.

Where can I find out more?

For more information about the importance of hydration and sweat sodium monitoring check out our other blog posts and keep an eye out for future updates. If you’re interested in using MX3 sweat testing at your team or worksite contact us to hear about our sweat testing packages.


1               American College of Sports, M. et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc 39, 377-390, doi:10.1249/mss.0b013e31802ca597 (2007).

2               Graudal, N., Jurgens, G., Baslund, B. & Alderman, M. H. Compared with usual sodium intake, low- and excessive-sodium diets are associated with increased mortality: a meta-analysis. Am J Hypertens 27, 1129-1137, doi:10.1093/ajh/hpu028 (2014).

3               Baker, L. B., Barnes, K. A., Anderson, M. L., Passe, D. H. & Stofan, J. R. Normative data for regional sweat sodium concentration and whole-body sweating rate in athletes. J Sports Sci 34, 358-368, doi:10.1080/02640414.2015.1055291 (2016).

4               Baker, L. B. et al. Exercise intensity effects on total sweat electrolyte losses and regional vs. whole-body sweat [Na(+)], [Cl(-)], and [K(+)]. Eur J Appl Physiol 119, 361-375, doi:10.1007/s00421-018-4048-z (2019).

5               Mikkelsen, C. J. et al. Prolonged heat acclimation and aerobic performance in endurance trained athletes. Frontiers in physiology 10 (2019).

6               McCubbin, A. J., Lopez, M. B., Cox, G. R., Odgers, J. N. C. & Costa, R. J. Impact of 3-day high and low dietary sodium intake on sodium status in response to exertional-heat stress: A double-blind randomized control trial. European journal of applied physiology 119, 2105-2118 (2019).

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