Electrolyte loss through sweating: what is really lost

What to expect in this article

1. What sweat is and what it is for
2. Why sweat changes on its way out
3. Three groups of substances, three very different losses
4. What is actually needed during exertion
5. How the body adapts to heat
6. Sweat and sodium in numbers
7. When replacement is even worth discussing
8. The mistake that is more dangerous than the loss
9. Three statements about sweating fact-checked
10. What a blood test can show here
11. Limits: what cannot be measured
12. What matters when sweating
Frequently asked questions
Sources

What sweat is and what it is for

Sweating is the most effective cooling mechanism the body has. When fluid evaporates from the skin, it removes heat, keeping body temperature within a safe range. Everything else in sweat is a by-product of this task.

The MSD Manual quantifies how much this cooling can be ramped up in its professional edition: under heat stress, sweat production rises from negligible levels to more than two liters per hour (2025).

Why salt is carried along in the first place

Sweat forms as fluid diverted from the space between cells. Whatever is dissolved there initially comes along. The body reclaims some of it on its way out, but not all of it.

How much is reclaimed depends on the rate. Baker’s review in the journal Temperature notes that higher sweat rates are associated with proportionally lower reabsorption rates, resulting in higher electrolyte concentrations in the final sweat (2019).

Why sweat changes on its way out

This section may sound like a minor technical detail, but it is the reason incorrect figures circulate online. The fluid produced in the sweat gland is considerably saltier than the sweat that ultimately reaches the skin.

A considerable portion of the sodium is reabsorbed on its way through the sweat duct. Anyone who cites the values from the first stage and presents them as the composition of sweat arrives at a multiple of the actual loss.

A second source of error lies on the skin

Baker also describes a measurement problem that undermines many widely circulating figures: contamination from the skin’s surface led to reported concentrations of trace elements such as iron and calcium that were two to five times higher (2019).

So if you read that sweat contains surprisingly much calcium or iron, you may be reading a measurement of the skin rather than the gland. This is not a peripheral issue but the crux of the debate about trace elements in sweat.

Three substance groups, three very different losses

Not everything found in the blood is lost through sweating to a comparable extent. The table compares the three groups according to the same four criteria.

The third column is the key finding of this article. It contradicts what is stated on most electrolyte powder packages.

What is actually needed during exercise

In 2019, the Sports Nutrition Working Group of the German Nutrition Society published a position paper on this topic. One sentence from it answers the question addressed in most advertising copy.

This refers to everything except water, carbohydrates, and sodium. In this list, magnesium, calcium, zinc, and potassium are among the other minerals whose intake during exercise is not necessary.

How the body adapts to heat

Salt loss through sweat is not a fixed quantity. It decreases when someone is regularly exposed to exertion in the heat. The MSD Manual quantifies this effect clearly: With heat acclimatization, sodium levels in sweat decrease by up to 60 percent (2025).

The adaptation takes time. According to the same source, acclimatization generally requires seven to fourteen days in the hot environment.

What this means in practice

Someone experiencing the first warm week of spring loses more salt at the same level of exertion than in midsummer. The same applies to someone who flies directly from winter to a warm holiday destination and immediately exercises there.

The reverse conclusion is equally useful. Anyone who has been working or training in the heat for weeks has already significantly reduced their losses without doing anything to cause it. The body regulates this itself if you give it two weeks.

Why the adaptation works at all

The body improves sodium reabsorption in the sweat gland's duct. So you do not sweat less—in fact, the opposite—but your sweat contains less salt. Cooling performance is maintained while the loss decreases.

This explains an everyday observation familiar to many people. In spring, sweat stings the eyes and leaves white marks on dark clothing; in midsummer, noticeably less so. The amount is the same; the composition is not.

Sweat and sodium in numbers

The following three figures come from the DGE working group's position paper and describe the same process. They are the only reliable figures this article has to offer.

Sweat in numbers

Source: Sports Nutrition Working Group of the German Nutrition Society, Fluid Management in Sports, as of 2019

What the range means

The range from 175 to 1,512 milligrams is almost ninefold. Two people can lose vastly different amounts of salt during identical exertion, and neither of them will notice.

That is why the DGE position paper also states that blanket recommendations for fluid intake during sports make little sense, because fluid losses vary greatly both between individuals and within the same person.

A calculation for context

One hour of running at 10 kilometers per hour means that, according to the example values in the DGE position paper, a person weighing 70 kilograms loses around 0.79 liters of sweat in cool weather and 0.89 liters in warm weather. Using the average of 900 milligrams of sodium per liter, that amounts to approximately 710 to 800 milligrams of sodium.

For comparison: The DGE's estimated value for an appropriate sodium intake is 1,500 milligrams per day, while actual intake in Germany is significantly higher. An hour of running therefore costs less sodium than many people already consume in excess every day.

When replacement is even worth discussing

The DGE position paper specifies clear thresholds. For exertion lasting less than 30 to 40 minutes, fluid intake is therefore not necessary, and minor fluid deficits are tolerable during exercise.

The second threshold is one hour. Anyone who starts adequately hydrated does not need to drink anything during endurance exercise lasting up to 60 minutes, according to the same position paper. Sodium is recommended only after about one and a half hours of exercise and when the sweat rate is high.

Where heat work is different

A different scale applies to people who work in the heat. The MSD Manual gives a clear figure here: workers, soldiers, endurance athletes, or other people who sweat heavily can lose 20 grams or more of sodium per day (2025).

Twenty grams is more than thirteen times the daily estimate. At this magnitude, replacement is no longer a matter of optimization but part of occupational safety. This explicitly does not apply to one hour of recreational exercise.

After exertion, the plate is usually enough

The position paper also offers reassurance about what comes afterward. If body weight has decreased by less than five percent, the DGE says that consuming normal meals and snacks combined with sufficient water intake is enough to restore fluid and electrolyte balance.

Five percent is three and a half kilograms of weight loss at 70 kilograms in a single session. Anyone who reaches that point knows it. Everyone else is adequately served by a normal dinner.

What can be in the glass instead

The DGE position paper identifies an alternative that appears in no advertising brochure because it costs nothing: fruit juice spritzers made from one part fruit juice and two parts high-sodium, low-carbonation mineral water are well suited as rehydration drinks.

Two details in this sentence are often overlooked. The mixing ratio is one part to two, not half and half, and the mineral water should be high in sodium. Anyone who drinks a ready-made spritzer made with low-sodium water has a drink without the component in question.

For the rare cases in which a drink during exercise is useful, the same source specifies a composition of 4 to 8 percent carbohydrates and 400 to 1,100 milligrams of sodium per liter. These are figures against which a label can be checked.

The mistake that is more dangerous than the loss

During prolonged endurance exercise, drinking too much is a greater risk than drinking too little. In the German Journal of Sports Medicine, Scheer and Hoffman describe exercise-associated hyponatremia as a serum sodium concentration below 135 mmol/L during or up to 24 hours after exercise (2018).

The frequency is surprising. According to the same study, the incidence varies by sport, from 11 percent in the Ironman Triathlon to 51 percent after a 161-kilometer ultramarathon; rates of up to 70 percent have been reported among rowers at a training camp.

Why this has little to do with salt loss

The authors cite hyperhydration caused by excessive fluid intake, together with an inappropriate release of the hormone arginine vasopressin and the resulting water retention, as the cause. The sodium is therefore diluted, not sweated out.

The authors’ recommendation is correspondingly simple: drinking according to thirst is an effective prevention strategy. Anyone who follows this sensation instead of a predetermined amount will not make this mistake.

Exercise-associated hyponatremia is a serious condition and requires medical treatment. Anyone who notices nausea, headaches, or confusion after prolonged exercise should not continue drinking, but should seek medical attention.

Three statements about sweating, fact-checked

The following three statements appear in almost every text on the subject. All three are so widespread that they are hardly questioned anymore.

Checked against the evidence

The first point deserves an addition, so that reassurance does not become a free pass. The fact that we found no figure does not mean that no magnesium is lost through sweat. It means that no one has reliably quantified this loss and that the available measurements are distorted by skin contamination.

What a blood test can show here

A blood test does not measure how much you have sweated. It shows where your concentrations stand at the time of sampling, and shows them together with the other electrolytes and trace elements.

The converse is also true. Baker's review notes that the usefulness of sweat composition as a biomarker of human physiology is currently limited because further research is needed to determine possible relationships between concentrations in sweat and blood (2019).

Capillary blood test

BalanceCheck | Electrolytes & minerals test

15 elements from a blood sample: sodium, potassium, calcium, magnesium, and phosphorus, plus six trace elements and four heavy metals. What the test does not do: It does not measure sweat loss or answer how much you have sweated. It does not provide a diagnosis, and there is no evidence-based indication for routine electrolyte testing in healthy recreational athletes.

Price €139.00 As of 08/11/2026, subject to change

Sample type Capillary blood

Processing time Kit shipping 1–3 business days
Laboratory analysis 3–5 business days after sample receipt

Laboratory certified medical testing laboratory
Product page information, accessed 08/11/2026

To BalanceCheck

A measurement is useful when there is a specific reason for it. The following four points describe what needs to be clarified beforehand.

Limitations: what cannot be measured

Individual salt loss through sweat cannot be determined outside a laboratory. The range of 175 to 1,512 milligrams per liter means that any calculation based on the average could be far off for you personally.

There is no data basis at all for trace elements. In the sources we reviewed, we found no reliable concentrations for magnesium and calcium in sweat, and the available measurements are distorted by skin contamination. That is why this article gives no figure for them.

A blood test does not close this gap either. It measures concentrations, not losses, and only at one point in time. For healthy recreational athletes, none of the sources reviewed contains a recommendation for routine blood electrolyte testing.

Another limitation concerns sweating itself. Excessive sweating can be harmless, but the MSD Manual points out that diffuse sweating, when accompanied by relevant findings, can also suggest infections, disorders of the endocrine system, or cancer, and that an asymmetric sweating pattern indicates a neurological cause (2024). Neither can be clarified by a blood test.

This list may read like an argument against measuring. It is not. It is an argument against expecting one value to represent a loss that is not actually present in the blood.

What matters when you sweat

If you take away one practical step from this article, let it be this: Weigh yourself once before and once after a typical training session, without clothes and without drinking in between. The difference in kilograms roughly corresponds to your fluid loss in liters.

The reason is unremarkable. This one figure tells you more about your personal loss than any average from an article, and it costs nothing except a set of scales. If it is below two percent of your body weight, the question of whether you need replacement is answered for you.

It began with the question of what is lost through sweating. The most honest answer is: water and salt—and less salt than advertising claims might suggest. For everything else, there is still no figure.

Frequently asked questions

Sources

1. Mosler S, Braun H, Carlsohn A et al. (DGE Sports Nutrition Working Group): Fluid management in sports. Ernährungs Umschau, 2019 – dge.de
2. MSD Manual, Professional Edition: Heat illness overview, Yip K, Tanen D, Birnbaumer DM (as of 2025) – msdmanuals.com
3. Scheer V, Hoffman MD: Exercise-associated hyponatremia. German Journal of Sports Medicine 10/2018 – zeitschrift-sportmedizin.de
4. Baker LB: Physiology of sweat gland function. Temperature 6(3), 2019 – pmc.ncbi.nlm.nih.gov

The verbatim quotation regarding the intake of additional minerals, information on sodium in sweat, sweat rate, exertion thresholds, the performance limit at 2 to 4 percent, and rehydration after exertion comes from source [1]. Maximum sweat rate, sodium loss during heat work, and information on heat acclimatization come from [2]. The definition, incidence, and cause of exercise-associated hyponatremia, as well as the recommendation to drink according to thirst, come from [3]. The assessment of sweat-related trace element deficiencies, the note on skin contamination, the relationship between sweat rate and reabsorption, and the statement regarding the limited suitability of sweat as a biomarker come from [4]. The information on warning signs of excessive sweating comes from the MSD Manual, Professional Edition, Hyperhidrosis (as of 2024); the estimated sodium intake is based on the DGE reference values (2016 derivation). Both are attributed in the text with the institution and year. Information on price, biomarkers, sample type, and laboratory comes from the mybody®x product page, accessed on 11 August 2026; processing times follow the central guideline for blood tests. All sources were accessed and reviewed on 11 August 2026.

mybody®x Editorial & Expert Team

Laboratory diagnostics Nutritional science Blood analysis interpretation Nutrigenetics

This article was created by the mybody®x editorial and expert team. The team combines laboratory diagnostics, nutritional science, and the interpretation of blood analyses. Everyone involved can be found on the authors' page.

Published on 11 August 2026 · Last updated on 11 August 2026

The content is provided for general information and does not replace medical advice, diagnosis, or treatment. Reference ranges depend on the laboratory, method, and age; the information on your test report is always authoritative.