Supplement Guide | Electrolytes 02 | What Sports Drinks Get Wrong About Sweat

This is part 2 of SuppCo's 3-part Supplement Guide on electrolytes. The series covers what electrolytes actually do in the body and why the market around them exploded, the research on when they actually matter for athletic performance, and a practical guide to what to look for when you buy one.

To read part 1 in the series, click here.

One in twelve. That's how many marathon finishers had hyponatremia, low blood sodium, show up in their blood tests, according to a 2022 review of several endurance races. That works out to an average of just over 8%. Most of these runners felt fine. They had no idea it happened.

 A smaller number just might matter even more. About 0.1% to 1% of endurance athletes get hyponatremia bad enough to need treatment. Picture a marathon with 30,000 finishers. At the low end, that's 30 people in the medical tent. At the high end, it's 300. A tiny percentage on paper turns into a long line for treatment at the finish. And the people in that line got there by drinking too much water, not too little.

Part 1 of this series showed that most people don't have a real electrolyte gap on a normal day. Exercise can change that. But it changes less than the marketing suggests, and the overall story is more complicated than one simple number. Exercise is where the evidence for adding electrolytes gets stronger. It's also where getting it wrong, in the other direction, can put someone in an ambulance.

Why Sweat Isn't the Same for Everyone

Sweat doesn't carry the same amount of sodium every time. As sweat forms inside a sweat gland, it passes through a duct on its way out. Special channels in that duct pull some sodium back into the body before the sweat reaches your skin. How much sodium gets pulled back depends on how fit you are, how heat acclimated you are, your genes, and how fast you're sweating. When you sweat fast, the duct has less time to grab that sodium back. That's why a hard, hot workout doesn't just make you sweat more. It makes each drop of sweat saltier, too.

A 2017 review in the journal Sports Medicine looked at sweat tests from many athletes. Sweat ranges from about 0.5 to 2.0 liters per hour. That's a fourfold difference from one person to the next. That means, using that same test, under the same conditions, one athlete's sweat can run four times heavier than someone else's.

Four times. That's the spread between the lightest sweaters and the heaviest ones, tested the same way, under the same conditions.

That range is why one sodium number can't work for every athlete. It also matters less than the next problem. Drinking too much water is what actually sends people to the medical tent.

Signs you're likely a "salty sweater":

• White marks on dark clothes, a hat, or your skin after a long or hot workout

• Stinging eyes from sweat during exercise

• Salt on your skin, or a salt craving, in the hours after training

• A history of cramping during long or hot workouts specifically, not short ones

The Overdrinking Problem (Hiding in Plain Sight)

Hyponatremia during exercise usually isn't about losing too much sodium. It's about drinking more water than your kidneys can remove. A healthy kidney can flush out roughly 800 to 1,000 milliliters of water an hour, even at rest. Drink faster than that for long enough, and the extra water dilutes the sodium in your blood directly. Long, hard exercise makes this worse. Pain, nausea, and physical stress keep a hormone called ADH turned on. ADH normally tells your kidneys to hold onto water. During long exercise, it can stay switched on even after your blood is already too diluted, which is exactly backward, and it stops your kidneys from clearing the extra water.

The advice that caused this problem meant well. "Drink as much as you can" was standard race advice for years, meant to prevent dehydration. It worked in that sense: dehydration became less common. But it created a separate, real risk of its own: drinking too much.

Even with time, this advice hasn't yet reached the athlete population. A study of 210 runners, surveyed before a Southern California marathon found similar results. 84% said they'd heard of exercise-associated hyponatremia. But only 32% could actually name a symptom of it. Fewer than 5% mentioned "drink to thirst" as a way to prevent it, even though that's been the official medical advice since 2015. Slower runners and first-time marathoners were the most likely to over-plan how much they'd drink. They also knew the least about hyponatremia. Combined… that creates significant risk.

A tiny percentage on paper turns into a long line at the finish-line medical tent. Most people got there by drinking too much water, not too little.

What the Performance Research Actually Shows

Before asking whether sodium helps you perform better, it helps to know what sodium actually does. It helps hold water inside your blood vessels, which keeps your blood volume up on a long effort, and your heart needs that volume to keep pumping efficiently. Sodium, along with potassium, also drives the electrical signal that lets a muscle or nerve fire at all. Both jobs matter more the longer you exercise.

The proof that electrolytes boost performance is notably weaker than the headlines suggest. A 2025 review of the clinical trial evidence found high-sodium drinks gave athletes a small edge over other options, but not a real, statistically meaningful one. Official sports medicine guidelines on sodium during exercise are designed to lower the risk of hyponatremia, not to boost performance… and when researchers tested a higher dose directly against a placebo, it made no difference to how athletes performed; this held regardless of whether it was long-term sustained exercise or short-term burst activities. Overdoing sodium regularly carries its own risk, like higher blood pressure, so more isn't automatically better.

What About Cramps?

The cramping marketing goes perhaps, furthest past the evidence. Scientists still argue about what actually causes exercise cramps: a sodium deficit, or nerve fatigue from overworked muscles. Some of the best support for the nerve explanation comes from an unlikely source: a 2022 trial that gave pickle juice to patients with a liver condition that causes frequent muscle cramps. Over a month, it cut their cramp severity significantly more than plain water did… even though a sip of pickle juice couldn't meaningfully change anyone's sodium levels. Researchers think a nerve reflex triggered in the throat is doing the work, not sodium reaching the bloodstream. Treating a cramp as proof of low electrolytes is, contrary to popular opinion, not supported by science.

Now, none of this means sodium doesn't matter. It just means the strongest reason to use them isn't a faster performance time or fewer cramps. It's more so about staying safe when fluid balance breaks down on a long, hot effort. Which is a much less flowery claim than marketing tends to make.

When the evidence for added sodium is strongest:

• Exercise lasting 60 to 90 minutes or longer without a break

• Hot or humid weather, which raises both your sweat rate and how salty your sweat is

• A confirmed heavy or salty sweat profile, from a sweat test or the signs above

• Endurance events over two hours, where the hyponatremia risk described above becomes real

• A history of cramping during long or hot workouts specifically, even with the unsettled science above

Individualizing It

How much sodium you lose overall is calculated as your sweat rate multiplied by how long you're sweating. That's why a marathon runner and a CrossFit athlete need different math, even if both sweat a lot. A marathoner sweating for 90 minutes or more builds up a real sodium loss over that time, even at a moderate rate. A CrossFit workout usually lasts under 60 minutes. The sweat rate can be very high, but the short time means the total loss usually stays smaller. That's why adding sodium during a long endurance effort makes sense. For a short, hard workout, it usually makes more sense to replace sodium afterward instead (or just drink water).

Sweat testing is the only way to get your own real number, instead of guessing from someone else's average. That means either a lab test that washes down your whole body, or a patch test worn during a workout. Without a sweat test, drinking when you're thirsty is the safest default. It matches your body's real fluid needs closely enough for most training and racing. It's also the exact habit fewer than 5% of surveyed marathon runners said they follow to prevent hyponatremia. The situations below are what should push someone past "just drink when thirsty" and toward planning sodium ahead of time.

Practical Guidance

• Under 60 minutes, in normal conditions: water alone is usually enough, for both endurance and HIIT-style training.

• 60–90+ minutes, in heat, or with a known heavy/salty sweat profile: 500 to 700 mg of sodium per liter of fluid, the range recommended by the International Society of Sports Nutrition for exercise lasting over an hour. Use the higher end if you're a confirmed salty sweater, the lower end if you're not.

• CrossFit or HIIT under 60 minutes with heavy sweating: replace sodium after the workout instead of during it. The total loss usually isn't enough to justify dosing mid-session.

Limitations Worth Knowing

The evidence behind these numbers isn't perfect. Studies use different temperatures, different workout lengths, and different types of athletes. That makes it hard to combine their results precisely, even in a careful review. Most trials in this area are also small. And they are shorter than a real marathon or triathlon. And after decades of research, scientists still don't agree on what exactly causes exercise cramps.

Electrolytes during exercise isn't something everyone needs. But it isn't nothing, either. It depends on how long you're moving, how hot it is, and how salty your own sweat is. It doesn't depend on what a bottle promises, or what a marathon expo booth is selling. Skipping electrolytes during a 40-minute workout is rarely an issue.

None of this tells you what to buy (or how to take it). Part 3 breaks down exactly what belongs on the label, and what's just marketing.