Every summer, emergency tents at marathons and triathlons fill up with athletes who did exactly what they were told: they drank plenty of water. The problem is that “drink more” became “drink too much.” Overhydration is a real and occasionally fatal risk, and it has a name: exercise-associated hyponatremia (EAH). If you train or race in the heat, understanding it is just as important as knowing how to avoid dehydration.
What Hyponatremia Actually Is
Hyponatremia is an abnormally low concentration of sodium in the blood — below roughly 135 millimoles per liter, against a normal range of about 136 to 142. Exercise-associated hyponatremia develops when an athlete takes in more fluid than the kidneys can excrete, usually over hours of activity. The excess water dilutes the sodium already in the bloodstream. Because sodium controls how water moves in and out of cells, that dilution pulls water into tissues — including the brain. In severe cases the resulting swelling causes confusion, seizures, coma, and death.
It is easy to assume this is rare, but in the right conditions it is not. Studies of ultramarathons over 100 kilometers in hot weather have found that 30 to 51 percent of finishers show some degree of hyponatremia, and long-course triathlons such as Ironman events report rates of 18 to 28 percent. The athletes most affected tend to be the ones who drink the most, not the least.
Why Summer Makes It Worse
Heat is a double-edged sword. It increases your sweat rate, so you genuinely need more fluid — but it also raises anxiety about dehydration, which pushes many athletes to drink at every opportunity regardless of thirst. The danger zone is the combination of long duration, plentiful aid stations, and a slower pace that leaves time to keep sipping. Mid- and back-of-pack finishers in marathons are statistically more likely to develop EAH than the leaders, simply because they are on course longer and drinking more.
The other overlooked factor is what you are drinking. Plain water and very low-sodium beverages dilute blood sodium fastest. A drink that contains meaningful sodium replaces some of what you are losing in sweat and helps keep blood sodium in a safer range. This is the core reason the “sodium-first” approach has gained traction among endurance coaches.
How Much Sodium You Actually Lose
Sweat is not just water. Every liter carries roughly 500 to 2,000 milligrams of sodium, and the concentration varies enormously between individuals. “Salty sweaters” — people who finish a hot session with white residue on their skin and stinging eyes — sit at the high end. Sweat rates themselves range from about 0.5 liters per hour to more than 3 liters per hour in hot, humid conditions. That means two athletes side by side can have wildly different sodium needs.
Research in the Journal of Athletic Training found that runners consuming 1,000 milligrams or more of sodium per hour during 90°F-plus marathons had significantly fewer heat-related medical issues, with cramping reduced by roughly 60 percent. The takeaway is not that everyone needs exactly that amount, but that sodium — not just fluid volume — is the variable most athletes underestimate.
Choosing a Drink That Carries Enough Sodium
This is where product choice matters. A traditional sports drink like Gatorade or Powerade provides carbohydrate and some electrolytes, but its sodium content (around 160 milligrams per 12 ounces) is modest for a heavy sweater in summer heat. Higher-sodium options have filled that gap. LMNT delivers 1,000 milligrams of sodium per packet, which is a lot and best suited to genuinely salty, high-sweat efforts. Nuun Sport and Skratch Labs sit in a more moderate range, pairing sodium with potassium and light carbohydrate for steady sipping.
Pickle juice has also earned a place in this conversation, and not just as a folk remedy. A serving is concentrated sodium, which is exactly what a depleted, cramp-prone athlete is short on. Brands like Fast Pickle have leaned into this, offering pickle-brine shots designed as a fast, high-sodium top-up rather than a primary hydration source. Used alongside your regular fluids, a small dose can help replace sodium quickly during or after a hot, salty session. The point across all of these is the same: match the sodium to your sweat, and do not rely on water alone to do a job it cannot do.
A Practical Summer Hydration Plan
Start by learning your own numbers. Weigh yourself before and after a one-hour session in similar heat; each pound lost is roughly 16 ounces of fluid you did not replace, and gaining weight during exercise is a warning sign of overhydration. Use that to estimate your sweat rate, then drink to roughly match it — not to exceed it.
During longer efforts, aim for a beverage providing somewhere in the range of 500 to 900 milligrams of sodium per liter, leaning higher if you are a salty sweater. Drink to thirst rather than on a rigid schedule, which is the single most protective habit against EAH. And learn the early warning signs: nausea, headache, bloating, puffy hands or fingers, and confusion. Those symptoms overlap with dehydration, but if they appear after you have been drinking heavily, the answer is almost never more plain water.
The Bottom Line
Hydration is not a contest to drink as much as possible. The athletes who stay safe and perform best in summer treat fluid and sodium as a pair, tailoring both to their own sweat. Water keeps you hydrated; sodium keeps that water where it belongs. Whether you reach for a measured electrolyte mix, a sports drink, or a quick pickle-brine shot, the goal is balance — enough fluid to replace what you lose, and enough sodium to hold the line.
This article is for general education and is not medical advice. If you experience confusion, severe headache, or vomiting during or after exercise, seek medical attention promptly.