How Much Sodium Do You Lose in Sweat? Electrolyte Dosing for Training

Athletes' sweat typically contains roughly 400 to 1,600 mg of sodium per liter. In a study of 506 athletes, the average was about 830 mg per liter. Athletes typically sweat 0.5 to 2 liters an hour during training, so hourly sodium losses can be anywhere from a few hundred milligrams to well over 2,000 mg. Your own number depends on how much you sweat and how salty your sweat is, and both vary widely from person to person.

Key takeaways

• Sodium is the electrolyte lost in the greatest amounts in sweat. Chloride is lost alongside it, and potassium and magnesium are lost in much smaller amounts.
• In 506 athletes, estimated whole-body sweat sodium averaged 35.9 mmol/L (about 830 mg/L). Individual values ranged from 18.2 to 70.8 mmol/L, roughly a fourfold spread.
• Weighing yourself before and after training is the simplest way to estimate your sweat rate. One kilogram lost is about one liter of sweat.
• For most sessions under an hour, water and normal meals are enough. Sports-nutrition guidance points to added sodium for sessions longer than 2 hours, sweat rates above 1.2 L per hour, or noticeably salty sweat.
• Drinking well beyond what you sweat is a risk of its own, and adding electrolytes does not cancel it out.

How much sodium is in sweat

Sweat starts out in the gland with about the same salt content as blood. As it moves up the duct to the skin, the body pulls much of the sodium and chloride back in, so the sweat that reaches your skin is far less salty than your blood. How much gets reabsorbed differs from person to person and changes with conditions. That is why sweat sodium is so variable.

In a 2016 study of 506 athletes, predicted whole-body sweat sodium averaged 35.9 mmol/L, with a range of 18.2 to 70.8 mmol/L. A joint position paper from the Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine (ACSM) uses a rounder average of about 50 mmol/L, roughly 1 g of sodium per liter, and stresses that it is highly variable. To convert, one millimole of sodium weighs 23 mg.

Your diet also changes the result. In studies reviewed by Baker, sweat sodium rose after 8–14 days of very high salt intake (8–9 g of sodium a day) and fell after a shift to low intake (1–2 g a day). Heat acclimation also helps the body hold on to more salt.

How much you sweat

Sweat rate matters as much as concentration. The joint position paper gives a typical range of 0.3 to 2.4 liters per hour, depending on intensity, duration, fitness, heat acclimatization, altitude and weather. Average rates differed by sport in a later analysis of 1,303 athletes. American football players averaged 1.51 L per hour, endurance athletes 1.28, basketball 0.95, soccer 0.94 and baseball 0.83. Average sodium losses in that dataset ranged from about 27 mmol an hour in baseball, about 630 mg, to about 56 mmol an hour in American football, about 1,290 mg. Individual athletes fell well above and below those averages.

Estimate your own sweat rate

1. Weigh yourself in minimal clothing right before a typical session, after using the bathroom.
2. Train as usual. Note how much you drink, in liters.
3. Towel off and weigh yourself again in the same clothing.
4. Calculate: (weight before minus weight after) plus fluid drunk, minus any urine passed, then divide by the hours trained. One kilogram (2.2 lb) is about one liter of sweat.

Repeat this in different conditions, such as a cool morning run and a hot afternoon session, because the result can change a lot. Multiply your liters per hour by an assumed sweat sodium concentration and you have a rough hourly loss. At an average concentration, one liter of sweat is about 830 mg of sodium. At the high end it is about 1,600 mg. Only a properly collected sweat test measures your actual concentration. Baker's review notes that results depend heavily on how the sample is collected and analyzed.

Sodium, chloride, potassium and magnesium

Sodium is the main electrolyte lost in sweat and the one that matters most for fluid balance outside your cells. Chloride travels with it, and the concentrations of both rise together as sweat rate increases. Potassium is the main electrolyte inside your cells and is involved in nerve signaling and muscle contraction. Sweat contains only about 2–8 mmol/L of it. Magnesium is involved in more than 300 enzyme systems, including energy production and muscle and nerve function, and appears in sweat in even smaller amounts. Day to day, most of your potassium and magnesium comes from food, not from replacing what you sweat out.

When water is enough, and when electrolytes make sense

The ACSM's fluid replacement position stand describes a goal of not losing more than about 2% of body weight to dehydration during exercise. It recommends individualized plans because sweat rates and sweat electrolyte content vary so much. It also notes that drinks containing electrolytes and carbohydrate can be more useful than water in some circumstances.

• Water is usually fine for sessions under about an hour in mild conditions, especially if you eat normally afterward. Food usually replaces the sodium you lost.
• Electrolytes make more sense for sessions longer than 2 hours, for heavy sweaters losing more than 1.2 L per hour, and for people with salty sweat. After training, the joint position paper suggests drinking about 1.25–1.5 liters for each kilogram lost, over time, and says not to restrict sodium after large sweat losses.

Over-hydration

Drinking well beyond what you sweat over long events can dilute blood sodium. An international consensus statement identifies overdrinking as the main cause of this. Gaining weight during exercise and events lasting more than 4 hours are among the listed risk factors. The same statement notes that sodium-containing drinks cannot offset persistent overdrinking, because they are much less salty than blood. It describes drinking to thirst as a safe individualized approach. Electrolytes are not a reason to drink more than you need.

If you have been told to limit salt

The Dietary Guidelines for Americans recommend that adults limit sodium to less than 2,300 mg a day. The average American eats about 3,400 mg. If a clinician has told you to limit sodium, or you have kidney problems or take blood pressure medication (including ACE inhibitors, ARBs or potassium-sparing diuretics, which affect potassium), check with them before using an electrolyte product.

Where MAXIS Hydrate Electrolyte Mix fits

Each stick of Hydrate Electrolyte Mix provides 600 mg sodium, 900 mg chloride, 300 mg potassium and 100 mg magnesium, plus 400 mg vitamin C. It is sugar free and has 5 calories. It is designed to replace sodium, chloride and potassium lost in sweat and to support normal fluid balance.† Using the averages above, one stick covers a meaningful share of the sodium in roughly one liter of sweat. That makes it a better fit for long, hot or very sweaty sessions than for a short gym workout.

Count each stick toward your daily sodium total. The 100 mg of magnesium also counts toward the NIH upper limit of 350 mg a day for magnesium from supplements. For long endurance days, the Endurance Stack pairs Hydrate with Organic Fermented Beets.

FAQ

How many milligrams of sodium do I lose per hour of exercise?

Multiply your sweat rate by your sweat sodium concentration. For someone sweating 1 L an hour at an average concentration, that is roughly 800–1,150 mg. Heavy sweaters with salty sweat can lose several times as much.

Do I need electrolytes for a 45-minute workout?

Usually not. Water and your next meal are generally enough unless it is very hot or you are training again the same day.

How do I know if I am a salty sweater?

Visible salt residue on dark clothing after training can be a hint, but it is not a measurement. A properly run sweat test is the only reliable way to know your sweat sodium concentration.

References

1. Baker LB (2017). Sweating rate and sweat sodium concentration in athletes: a review of methodology and intra/interindividual variability. Sports Medicine. PubMed
2. Baker LB, Barnes KA, Anderson ML, Passe DH, Stofan JR (2016). Normative data for regional sweat sodium concentration and whole-body sweating rate in athletes. Journal of Sports Sciences. PubMed
3. Barnes KA, Anderson ML, Stofan JR, et al. (2019). Normative data for sweating rate, sweat sodium concentration, and sweat sodium loss in athletes: an update and analysis by sport. Journal of Sports Sciences. PubMed
4. Thomas DT, Erdman KA, Burke LM (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: nutrition and athletic performance. Journal of the Academy of Nutrition and Dietetics. DOI
5. American College of Sports Medicine (2007). American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine and Science in Sports and Exercise. PubMed
6. Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. (2015). Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. British Journal of Sports Medicine. BJSM
7. U.S. Food and Drug Administration. Sodium in your diet. FDA
8. NIH Office of Dietary Supplements. Potassium: fact sheet for health professionals. NIH ODS
9. NIH Office of Dietary Supplements. Magnesium: fact sheet for health professionals. NIH ODS

†These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.