How Many Electrolytes Do You Lose in Sweat During Exercise?

🧠 Article Difficulty: Intermediate
🕒 8 minute read

If you are wondering how much sodium and other electrolytes you lose while sweating so that you can make an informed decision regarding electrolyte replacement strategies, then this article is for you.

When we exercise, we sweat, and when we sweat, we lose electrolytes. The more we sweat, the more electrolytes we lose. But how many do we lose, and do they need to be replaced? This article looks at actual research data from multiple sweat loss studies, which are referenced throughout, to show exactly how much sodium, potassium, calcium, and magnesium we lose during exercise.

Navigation:

• Sweat loss per hour
• Electrolyte losses
• Sodium losses in endurance athletes
• Electrolytes and exercise performance
• Do you need to supplement?
• Further learning: what are electrolytes?

How much do we sweat per hour?

To determine electrolyte losses, we need to know how much we sweat per hour while exercising.

Data from a large research study of 506 athletes of various disciplines showed that typical sweat losses during exercise range from 1.0 to 1.9 litres per hour depending on conditions, exercise intensity and individual sweat rates (1).

Individual sweat losses typically varied from 0.6 to 2.6 L/hour, as people sweat different amounts. However, the authors were able to average the sweat losses and group them according to exercise intensity:

• Lower intensity or cooler conditions = 1.0 L/hour
• Moderate intensity or warmer conditions = 1.5 L/hour
• High intensity or hot conditions = 1.9 L/hour
• Very high intensity, very hot conditions, or being a heavy sweater = >1.9 L/hour

Electrolyte losses

Using data from various research studies on electrolyte losses in sweat, here are the average electrolyte values lost per hour at the different exercise intensities:

Lower intensity exercise (1.0 litres of sweat)

• Sodium: 826 mg - 860 mg
• Potassium: 222 mg - 366 mg
• Calcium: 44 mg
• Magnesium: 10 mg

Higher intensity exercise (1.9 litres of sweat)

• Sodium: 1570 mg - 1634 mg
• Potassium: 422 mg - 695 mg
• Calcium: 84 mg
• Magnesium: 19 mg
  

As you can see, sodium is by far the most heavily excreted during sweat loss, followed by potassium. Calcium and magnesium are lost in much smaller amounts and replacement is not strictly necessary to aid exercise performance.

Note that these are averages from research on athletes across various disciplines. Individual losses vary significantly. Some people lose more, while others less.

Losses in sodium have been reported as high as 6,000 mg in a single hour, and potassium as high as 581 mg (2), which highlights how individual sweat response, exercise intensity, and climate conditions play a huge role. 

Another factor is the type of exercise. Athletes performing continuous endurance exercise such as running or cycling will typically sweat more than those in sports like tennis or soccer, which include more frequent rest periods (1).

Sodium losses are higher in endurance athletes

Interestingly, research looking specifically at endurance athletes showed that not only does sweat volume increase with intensity, but the actual concentration of sodium per litre of sweat also increases (2). Meaning that as exercise intensity increases, not only does sweat volume increase, but sodium concentration in the sweat increases as well.

The data showed sodium losses were as follows: low intensity ~700 mg/L, moderate intensity, 940 mg/L, high intensity 1,130 mg/L. This means if you're an endurance trained athlete training at a high intensity, and sweating at a rate of 1.9 litres per hour, you can expect to lose 2150 mg of sodium every hour (1) (2).

Given these levels of electrolyte loss, particularly sodium, replacing electrolytes becomes important for maintaining exercise performance.

Electrolyte replacement and exercise performance

Electrolyte replacement during prolonged exercise can improve performance compared to water alone. However, for any benefit to be seen, bouts of exercise need to be long enough to induce enough sweat loss to deplete stored electrolytes (3) (4). 

For example, A study on 26 triathletes competing in a half-Ironman provided one group with ~500–600 mg of sodium per hour (via salt capsules) in addition to their normal fluid and food intake, while the control group received a placebo. The sodium group completed the race ~7.8% faster than the control group (5).

In a controlled crossover study (3), nine male participants completed three 48-hour dietary conditions: normal energy intake with adequate electrolytes, low energy intake (~33% of requirements) with electrolytes, and low energy intake (~33%) without electrolytes. This design allowed for a direct comparison of electrolytes vs no electrolytes under identical calorie-restricted conditions, used to simulate a stressed state such as prolonged exercise. After completing each 48-hour period of controlled diet and supplementation, participants performed a cycling test to exhaustion at ~60% VO₂ peak in hot conditions (~35°C). Exercise capacity was significantly better in the electrolyte group, with an improvement of ~10.5 minutes (~19%). Performance in the electrolyte condition was also close to the control group who were not calorie restricted. These findings suggest that electrolytes can prevent the decline in performance seen with energy restriction.

Generally, effects are only seen during prolonged exercise protocols (7). i.e., you don’t need electrolyte replacement unless you’re losing significant amounts through prolonged sweating. While an exact duration to warrant supplementation can't be given, as it depends on intensity, heat, and individual sweat losses, it's safe to say that electrolyte replacement is unlikely to have a meaningful effect on exercise bouts below 60 minutes

Replacing lost electrolytes, especially sodium, becomes increasingly important as exercise duration increases to maintain fluid balance and support normal muscle and nerve function, while helping reduce the risk of imbalances that can contribute to fatigue. As fluid and sodium losses increase, reductions in plasma volume and disruptions in electrolyte balance can impair muscular performance, thermoregulation, and cardiovascular function (6). Replacing electrolytes, particularly sodium, helps sustain fluid balance, maintain blood volume, and support continued performance.

Danger of very low sodium

Very low sodium levels dilute blood sodium concentration, causing water to move into cells (osmosis), which can lead to hyponatremia. When sodium drops too low in the blood, often from sweat loss combined with excessive water intake, this creates a concentration imbalance between the blood and cells. Cells swell, including brain cells, increasing intracranial pressure and potentially causing headaches, nausea, and vomiting. Severe hyponatremia can be dangerous. At higher levels of sodium loss, this can contribute to fatigue, headaches, and nausea, and in severe cases where water is consumed without sodium during very heavy sweat loss, the risk of hyponatremia increases (11).

Electrolytes + carbohydrate during exercise is best for performance

Most of the exercise performance research combines electrolytes with carbohydrates, which together represent the optimal strategy to support prolonged performance (8) (9). Carbohydrate + electrolyte solutions have been shown in multiple endurance exercise studies to significantly improve performance by supporting both energy delivery and hydration status (10). 

For example, a meta-analysis of 50 studies in running and cycling found that carbohydrate intake of 30–80 g/h improves time trial performance by ~2.0%, with larger improvements observed in time to exhaustion (15.1 %, and even greater 54.2% improvement when already pre-fatigued) (10). 

Do you actually need to supplement?

If you are engaging in prolonged (90 minutes+) endurance exercise at a decent intensity, then you should strongly consider electrolyte supplementation. However, there seems to be a common trend where people who don’t train hard or sweat heavily are buying hydration products unnecessarily. If you’re consuming high amounts of sodium without meaningful sweat losses on a regular basis, not only is this unnecessary, but it may contribute to elevated blood pressure over time as you are not excreting the increased sodium intake. Therefore, if you are a casual exerciser who goes to the gym once or twice a week, you likely don’t need to be consuming electrolytes. These products are designed for endurance athletes who train hard, sweat heavily, and exercise multiple times per week.

If, however, you are sweating frequently, supplementation can improve performance, but you must be careful to avoid the many gimmicky ‘hydration’ supplements on the market that are significantly underdosed in sodium and designed for general ‘lifestyle’ use (e.g. Cira, Organika, BioSteel). If you are looking for the optimal electrolyte supplement to support your training, check out our guide to the best electrolyte supplements in Canada, where we compare 8 products side by side against the sweat loss data above to determine the most effective electrolyte replacement option. 

Thrive Hydrate & EnduraFuel

Thrive Hydrate is designed according to the sweat loss data in this article. If you are looking for a Canadian-made, evidence-based electrolyte supplement, take a look at the product formula and see if it meets your needs. 

Research consistently shows that the optimal solution for endurance exercise should contain both carbohydrates and electrolytes (8) (9). Thrive EnduraFuel is designed to provide these together in scientifically optimized ratios to maximise exercise performance. If you are an endurance performer looking to optimize your training, this is the product for you. 

Further Learning

What actually are electrolytes?

Electrolytes are minerals that carry an electrical charge when dissolved in fluid (such as blood or intracellular fluid).

The main electrolytes in the human body include sodium, potassium, calcium, magnesium, chloride, phosphate, and bicarbonate. Chloride, phosphate, and bicarbonate are not often discussed in the context of exercise, as chloride is typically consumed alongside sodium as sodium chloride (salt), while phosphate and bicarbonate are not lost in meaningful amounts in sweat and are therefore not usually considered in electrolyte replenishment. The primary electrolytes considered in replenishment are sodium (and chloride), potassium, calcium, and magnesium.

Sodium

Sodium and potassium maintain electrochemical gradients across cell membranes via the sodium–potassium pump (Na⁺/K⁺-ATPase). This pump moves sodium out of the cell and potassium into the cell, creating a charge difference across the membrane. This gradient is essential for nerve signaling (action potentials), muscle excitation and contraction, and normal cellular function. The sodium-potassium pump is used in cells throughout the body - if you are interested in learning more about how it works, this 2-minute video gives a good explanation. 

Sodium also plays a key role in fluid balance and hydration. It is the primary extracellular electrolyte and helps regulate plasma volume and water retention. This is why sodium is the most important electrolyte lost in sweat and the primary driver of rehydration.

Chloride works alongside sodium as the primary extracellular anion (negatively charged ion) and is important for fluid balance and osmotic pressure, acid–base balance (via bicarbonate exchange), and the formation of hydrochloric acid (HCl) in the stomach for digestion.

Potassium

Potassium, in addition to its role in the sodium–potassium pump, is critical for restoring membrane potential after depolarization, allowing for proper nerve and muscle function. It also plays a role in regulating fluid balance within cells.

Calcium

Calcium is required for muscle contraction. When a muscle is stimulated, calcium is released within the muscle cell, allowing actin and myosin to interact and generate force. Calcium also contributes to nerve transmission and cell signaling. Losses are relatively low in sweat (roughly 44 mg per litre) and dietary intake is typically sufficient, so it is not strictly necessary to replenish during exercise.

Magnesium

Magnesium supports muscle relaxation and overall neuromuscular function. It acts as a cofactor for hundreds of enzymes involved in energy metabolism, protein synthesis, and nerve function. Magnesium helps regulate calcium activity, counterbalancing its role in contraction and allowing the muscle to relax. Magnesium is lost in very small amounts in sweat (roughly 10 mg per litre), so it is not necessary to replenish during exercise, although supplementation may still be beneficial and is a useful addition to an electrolyte formula.

Choosing the right electrolyte supplement

If you believe supplementation may improve your performance, check out our two electrolyte brand comparison articles below, which use the sweat loss research discussed in this article and compare it directly against electrolyte products.

• 8 Best Electrolyte Powders in Canada (Scientific Guide)
• Best LMNT Alternatives in Canada

Or if you are looking to explore the best carbohydrate + electrolyte products, check out this product comparison guide. 

About the Author:

Joe is a certified personal trainer, strength and conditioning coach, and nutrition coach. He holds a Bachelor of Science with Honours in Sport and Exercise Science, graduating with First Class standing. During his studies, Joe focused on human physiology and performance, and he applies this knowledge of exercise science to his work with Thrive. He is the co-founder of Thrive Protein, a Canadian family-run supplement company focused on clean, scientifically backed nutrition products, including protein powders, greens, and electrolytes.