04/14/2026
What Runners Need to Know About Hyponatremia (Overhydration)
When runners think about hydration, the message has always been clear: drink, drink, and drink some more. Water bottles, hydration packs, and aid stations every mile have become standard equipment for anyone serious about the sport. And for good reason—dehydration is dangerous. But there is another risk that many runners have never even heard of, and it can be just as deadly: hyponatremia, or overhydration.
Hyponatremia occurs when you drink so much water that your body's sodium levels become dangerously diluted. Sodium is essential for nerve function, muscle contractions, and maintaining fluid balance. When levels drop too low, cells begin to swell—including cells in the brain. The result can range from mild nausea to seizures, coma, and even death.
In this article, learn what causes hyponatremia, who is most at risk, and how to hydrate properly so you can stay safe on your next run.
What Is Hyponatremia?
The term "hyponatremia" comes from Greek and Latin roots meaning "low salt in the blood." Medically speaking, it is defined as a serum sodium concentration below 135 mmol/L. For runners, this typically happens when fluid intake exceeds fluid loss over a prolonged period.
Here is the paradox: hyponatremia is most common in endurance events like marathons and ultramarathons—exactly the situations where runners are trying their hardest to stay hydrated. According to a study in the Clinical Journal of Sport Medicine, up to 13% of marathon runners develop some degree of hyponatremia, and in some events, as many as 30% of finishers are affected.
Symptoms to Watch For
The early symptoms of hyponatremia can be easy to mistake for dehydration or just feeling "off" during a long run. That is what makes it so dangerous.
Mild to moderate symptoms include:
Nausea and vomiting
Headache
Bloated feeling or swelling in hands and feet
Restlessness and irritability
Severe symptoms include:
Confusion and disorientation
Seizures
Difficulty breathing
Loss of consciousness or coma
If you or a fellow runner experience these symptoms, especially after drinking large amounts of water during a race or long training run, seek medical help immediately.
Who Is Most at Risk?
Not every runner is equally vulnerable. The following factors increase your risk of hyponatremia:
Slow runners. The longer you are on the course, the more opportunities you have to overdrink. Faster runners finish before they can consume dangerous amounts of fluid.
Smaller runners. Women and smaller-framed individuals have lower total body water volume, meaning sodium dilution happens more quickly.
Runners who drink at every aid station. Many well-intentioned runners force themselves to drink at every water stop, even when they are not thirsty.
Runners taking certain medications. NSAIDs (like ibuprofen), antidepressants, and diuretics can affect kidney function and sodium regulation.
How to Hydrate Safely
The good news is that hyponatremia is entirely preventable. Here is what you need to know:
No. 1: Drink to thirst, not on a schedule. Your body has a built-in hydration monitor for a reason. If you are not thirsty, do not force yourself to drink. This single change prevents the vast majority of hyponatremia cases.
No. 2: Replace sodium, not just water. During runs longer than 60-90 minutes, especially in hot weather, you need electrolytes. Sports drinks, salt tablets, or salty snacks (pretzels, salted nuts, or even just a pinch of salt in your water bottle) help maintain sodium balance.
No. 3: Weigh yourself before and after long runs. This is the most accurate way to measure your hydration needs. A loss of 1-2% of body weight is normal and safe. If you gain weight after a run, that is a red flag for overhydration.
No. 4: Be careful with NSAIDs before racing. Ibuprofen and similar drugs are common among runners managing aches and pains. But they can impair kidney function and increase hyponatremia risk. Consider acetaminophen (Tylenol) as a safer alternative if you need pain relief during a race.
No. 5: Know the conditions. Cool, cloudy days require less fluid than hot, sunny ones. Do not use the same hydration plan for a 50-degree race as you would for an 80-degree race.
The Importance of Life ID for Runners
For runners who train or race alone, carrying a Life ID is one of the smartest safety precautions you can take. Hyponatremia can cause sudden confusion, seizures, or loss of consciousness—symptoms that look very different from dehydration or heat stroke. When first responders arrive on scene, they need to know what they are dealing with. If they assume you are dehydrated and give you IV fluids, that treatment could actually make hyponatremia worse and push you into a medical crisis. Without your medical information, they cannot know the difference.
Life ID provides a simple, reliable solution for runners. Unlike traditional engraved jewelry that has limited space, Life ID uses a durable QR code that first responders can scan instantly. This code links to a secure, detailed medical profile containing your conditions, medications, allergies, and emergency contacts. If you have a history of hyponatremia, kidney issues, or take medications that affect sodium levels, that information is critical. The QR code can be worn on a wristband, attached to a running belt, or placed on a shoe tag—designed to stay secure even during intense activity. Best of all, you can update your profile anytime online. If your health changes or you start a new medication, there is no need to buy a new ID. Just log in and update. Life ID grows with you, ensuring your emergency information is always accurate and up to date.
Takeaway
Hydration is not just about drinking enough water—it is about drinking the right amount. For runners, understanding hyponatremia could save your life. Drink to thirst, replace sodium on long runs, and listen to your body rather than following rigid hydration rules.
Do not let an unexpected medical emergency leave you without a voice. Get your Life ID QR today and ensure that when every second counts, first responders have the information they need to treat you correctly.
