Runners take salt tablets to replace the sodium they lose through sweat during long runs. Sodium is the primary electrolyte lost in sweat, and losing too much of it can lead to drops in blood volume, impaired performance, and in severe cases, a dangerous condition called hyponatremia. The American College of Sports Medicine recommends 300 to 600 mg of sodium per hour during prolonged exercise lasting more than two hours to reduce dehydration risk and help prevent hyponatremia.
How Much Sodium Runners Actually Lose
Sweat contains far more sodium than any other electrolyte. Whole-body sweat sodium concentration typically ranges from about 10 to 70 millimoles per liter, which translates to roughly 230 to 1,610 mg of sodium per liter of sweat. That range is enormous, and it explains why some runners feel fine without any supplementation while others cramp up or feel terrible during a long race.
How much you personally lose depends on genetics, fitness level, heat acclimatization, and how heavily you sweat. A runner producing 1.5 liters of sweat per hour at the higher end of sodium concentration could be losing well over 2,000 mg of sodium per hour. That’s more than the average person consumes in an entire meal. Over the course of a marathon or ultramarathon, those losses add up fast, and food and plain water alone may not keep pace.
What Sodium Does During Exercise
Sodium’s main job is maintaining the volume of fluid outside your cells, including your blood plasma. It acts like a sponge for water: where sodium goes, water follows. When sodium levels in your blood drop, your body can’t hold onto fluid as effectively, blood volume shrinks, and your heart has to work harder to deliver oxygen to working muscles.
This is also why drinking plain water during a long event isn’t always enough. If you’re sweating out sodium but only replacing the water, you dilute the sodium that’s left in your bloodstream. Taken to an extreme, this leads to exercise-associated hyponatremia, defined as a blood sodium level below 135 millimoles per liter during or up to 24 hours after physical activity. Hyponatremia can cause nausea, confusion, seizures, and in rare cases, death. It’s most common in slower marathon and ultramarathon runners who drink large volumes of water without replacing electrolytes.
Do Salt Tablets Prevent Muscle Cramps?
This is one of the most common reasons runners reach for salt tablets, but the science is surprisingly thin. The traditional explanation was that losing sodium and becoming dehydrated caused exercise-associated muscle cramps. It’s an intuitive theory, but multiple studies have failed to confirm it. A 2022 review in the International Journal of Environmental Research and Public Health concluded there is no documented scientific evidence for a direct relationship between sodium depletion and exercise-associated muscle cramps.
Current thinking points more toward neuromuscular fatigue as the primary cause of cramping during exercise. Your muscles cramp when the nerve signals controlling them become overexcited, typically from pushing harder or longer than your body is conditioned for. That said, many runners swear salt tablets help with cramps, and the placebo effect is powerful. It’s also possible that maintaining overall fluid balance through sodium intake indirectly reduces cramping in some individuals, even if sodium depletion isn’t the direct trigger.
Salt Tablets vs. Electrolyte Drinks
Salt tablets are popular because they’re compact, easy to carry, and deliver a precise dose of sodium without the sugar or bulk of sports drinks. But they come with real trade-offs.
A salt capsule has to dissolve in your stomach before the sodium can be absorbed, and that process requires adequate water. If you swallow a capsule without drinking enough fluid alongside it, you’re dropping a concentrated lump of salt into your gut. Highly concentrated sodium solutions slow stomach emptying and can actually reverse fluid absorption, pulling water into your intestines instead of your bloodstream. This can cause nausea, bloating, and stomach distress mid-run.
Electrolyte drinks, by contrast, arrive in your stomach already dissolved and can begin delivering sodium within minutes. The dilute nature of sports drinks is generally gentler on the stomach during exercise. They also combine sodium with carbohydrates, which aids absorption and provides fuel at the same time. Sipping a drink throughout a run delivers sodium in a steady, gradual stream, while capsules deliver it in a concentrated burst that you have to time manually.
From a practical standpoint, many runners find it easier to sip one bottle that handles hydration, electrolytes, and some energy rather than juggling pills, water, and gels separately. The salty taste of an electrolyte drink can also serve as a built-in reminder to keep drinking. That said, salt capsules still make sense in situations where carrying liquid is impractical, when you’re already getting enough water at aid stations, or when you need extra sodium beyond what your drink provides.
How Much Sodium to Take
The ACSM guideline of 300 to 600 mg of sodium per hour during exercise lasting longer than two hours is a reasonable starting point. Most commercial salt capsules contain somewhere between 200 and 400 mg of sodium per pill, so one or two capsules per hour with adequate water puts you in that range.
But individual needs vary dramatically. A light sweater running in cool weather may not need any supplementation at all, while a heavy sweater racing in heat and humidity might need the upper end of that range or more. The best approach is to experiment during training runs rather than trying something new on race day. Pay attention to how you feel, whether you notice white salt stains on your clothes (a sign of high sweat sodium concentration), and whether you gain or lose weight during long runs.
Risks of Taking Too Much
While sodium replacement during endurance exercise is generally beneficial, overdoing it carries real risks. Excessive sodium intake can cause nausea, vomiting, and significant gastrointestinal distress, particularly when capsules are taken without enough water. In extreme cases, very high sodium intake can lead to hypernatremia, the opposite of hyponatremia, where blood sodium climbs too high.
There’s also individual variation in how efficiently your kidneys clear excess sodium. Some people are genetically “salt-sensitive” and more vulnerable to the effects of acute sodium loading, while others handle excess sodium without issue. For most runners following the 300 to 600 mg per hour guideline and drinking appropriately, the risk of overconsumption is low. The bigger practical concern is stomach problems from taking capsules without enough fluid, which can derail a race faster than the sodium deficit you were trying to prevent.