Trail First Aid: Overhydration

Some runners know a lot about the dangers of overhydration. They know how to avoid it, how to help others avoid it, how to recognize its symptoms, and what to do to treat it. Maybe they’ve even read Dr. Tracy Hoeg’s superb Running on Science column article, “Exercise-Associated Hyponatremia: The (Not So) Salty Truth.” But a lot of runners don’t know much about overhydration. Or what they think they know isn’t quite right. And severe overhydration, like severe dehydration, can have dangerous consequences.

Take the following 10-question quiz to see where you fall on hydration-genius spectrum. You’ll either confirm your expertise or you’ll learn something. Either way, you’ll finish feeling good about your ability to help others.

Overhydration (Hyponatremia) Quiz

Question 1. TRUE or FALSE: You can drink too much water during a run.

If you answered TRUE: Good job with an easy question! Move on to Question 2.
If you answered FALSE: Scroll down to the answers and read Answer 1.

Question 2. TRUE or FALSE: You can drink too much sports drink during a run.

If you answered TRUE: Nicely done! Move on to Question 3.
If you answered FALSE: Scroll down to the answers and read Answer 2.

Question 3. TRUE or FALSE: Salt supplements won’t prevent overhydration problems.

If you answered TRUE: Brilliant! Move on to Question 4.
If you answered FALSE: Scroll down to the answers and read Answer 3.

Question 4. TRUE or FALSE: Overhydration is common at marathons and ultramarathons.

If you answered TRUE: Superstar! Move on to Question 5.
If you answered FALSE: Scroll down to the answers and read Answer 4.

Question 5. TRUE or FALSE: You can tell that someone is overhydrated by looking at them.

If you answered TRUE: Scroll down to the answers and read Answer 5.
If you answered FALSE: You’re ultra-smart! Move on to Question 6.

Question 6. TRUE or FALSE: You can tell if someone is overhydrated by asking how much they’ve had to drink.

If you answered TRUE: Scroll down to the answers and read Answer 6.
If you answered FALSE: Your brain is huge! Move on to Question 7.

Question 7. TRUE or FALSE:  You can tell if someone is overhydrated by asking how much they’ve peed.

If you answered TRUE: Scroll down to the answers and read Answer 7.
If you answered FALSE: Expert level! Move on to Question 8.

Question 8. It is difficult to distinguish between the symptoms of overhydration and dehydration.

If you answered TRUE: Scroll down to the answers and read Answer 8.
If you answered FALSE: Muy inteligente! Move on to Question 9.

Question 9. TRUE or FALSE: The treatment for overhydration is to stop drinking.

If you answered TRUE: Rock star! Move on to Question 10.
If you answered FALSE: Scroll down to the answers and read Answer 9.

Question 10. TRUE or FALSE: Overhydration is a much better name for being overhydrated than hyponatremia is.

If you answered TRUE: You are a genius! Tell your friends and then move on to the scenario. (Or read the answers and further confirm your brilliance before moving on to the scenario.)
If you answered FALSE: Scroll down to the answers and read Answer 10.

Overhydration Quiz Answers

Answer 1. It is definitely possible to drink too much water during a run. You’d think your kidneys would get rid of the excess fluid, but sometimes that doesn’t happen. Sometimes, a hormone is released that prevents you from peeing the excess fluid out. If you want to know more about how this hormone works and how exercise sometimes causes it to be released, read Dr. Tracy Hoeg’s, “Exercise-Associated Hyponatremia: The (Not So) Salty Truth.” (It’s so good!)

If you can’t pee off the excess fluid you’re taking in, it builds up. It dilutes your blood. Your cells swell. Ultimately, if you keep taking in too much fluid, your brain cells swell too. Seizures, coma, and even death can follow.

Answer 2. You can definitely overhydrate using sports drinks! Remember, they’re mostly water. The overhydration equation doesn’t change just because sports drinks contain electrolytes. If you drink too much fluid of any kind while you’re running, and a hormone gets released that prevents you from peeing the excess out, the fluid builds up. It dilutes your blood. Your cells swell. Ultimately, if you keep taking in too much fluid, your brain cells swell too. Seizures, coma, and even death can follow.

Answer 3. Salt supplements won’t prevent overhydration problems. Overhydration is a fluid-intake problem, not a salt-loss problem. You dilute your blood when you drink too much and you’re not able to pee out the excess. There’s the same amount of salt in your blood when you’re overhydrated as when you’re not; the salt’s just not as concentrated. Taking a sodium-tab to treat drinking too much water is like dumping a packet of salt in a freshwater lake and hoping for salt water. Sodium supplements won’t prevent or fix overhydration.

Answer 4. Mild and moderate overhydration is very common at marathons and ultramarathons. Here are three reasons why:

  • Many runners believe they can’t trust how thirsty they feel to let them know how much and when to drink. They’ve been told they should drink a certain amount of fluid every hour. But how much fluid you need every hour depends on a lot of factors including your body size and the outside temperature. Drop the schedule and drink when you’re thirsty.
  • The symptoms of overhydration are often confused with dehydration. Headache, weakness, and fatigue are common symptoms of mild and moderate overhydration. If you complain of these symptoms, your pacer, your crew, and the aid-station volunteers will usually assume you’re dehydrated. They’ll insist you drink more. You’ll probably figure they’re right and comply.
  • It usually takes athletes four or more hours of exercise and consistent fluid intake to become overhydrated. That’s pretty much a description of what we’re doing during all ultras and a lot of trail marathons too. We’re set up to become overhydrated if we drink beyond our thirst.

Answer 5. No, you can’t tell whether someone is overhydrated by looking at them. You can’t tell whether they’re dehydrated either. Your skin is an unreliable diagnostic tool for all kinds of medical and environmental emergencies. Swelling and bloating is common with overhydration, but you won’t be able to look at someone and see that. You’ll have to ask questions to try to figure out whether a runner is overhydrated, “Do you feel bloated or swollen? Do your clothes feel tight? Does your watch band feel tight?” This symptom is not always present.

Answer 6. You usually can’t tell if a runner has had too much to drink simply by asking how much they’ve drunk. That’s because ‘too much fluid’ varies from person to person depending on body size, exertion level, and temperature. What’s too much fluid for me, a 100-pound female, is likely different than your ‘too much.’ And what’s too much fluid for me in Texas when it’s 90 degrees Fahrenheit is different than what’s too much for me in the mountains when it’s 40 degrees Fahrenheit. Sometimes, it’s quite clear when fluid intake is excessive. Other times, that number is just one piece of the puzzle. It’s important note how long the runner has been drinking that much fluid. It usually takes more than four hours of excessive drinking to become overhydrated.

Answer 7. You can’t rely on urine output to determine whether someone is overhydrated. Remember, overhydration is a problem because your kidneys can’t get rid of the excess fluid. You might not pee at all when you’re overhydrated, or you might just pee a little bit. Sounds a lot like dehydration, doesn’t it?

Answer 8. It’s actually easy to distinguish overhydration from dehydration. You can simply ask, “Are you thirsty?” If a runner is thirsty, they’re dehydrated. If they’re not thirsty, it’s something else. If they’re not thirsty and have the following symptoms, then they are likely overhydrated:

  • A history of heavy water intake usually over four or more hours
  • Headache
  • Unusual weakness or fatigue
  • Swelling and bloating
  • Nausea and/or vomiting

Answer 9. The treatment for mild and moderate overhydration is to stop drinking. That’s it. You caused the problem by drinking too much. You can fix the problem by not drinking any more. Eventually your kidneys will kick in and get rid of the excess fluid.

If a runner is confused or has a decreased level of consciousness with a history of prolonged water intake, they need to be taken to a hospital as quickly as possible. Their brain is swelling, and they need an IV of highly concentrated saline solution to draw the fluid out of their brain.

Answer 10. Overhydration is a much better name for being overhydrated than hyponatremia is. Overhydration communicates both the problem and the solution. You drank too much. Stop drinking. Hyponatremia makes you think you’re dealing with a salt-loss problem. The word literally breaks down like this: ‘hypo’ = low, ‘natr’ = sodium, and ‘emia’ = blood. ‘Low salt in the blood.’ But remember, you haven’t lost salt. You’ve just diluted your blood by taking on too much water. It’s a relative salt loss. You don’t need more salt. You need to stop adding water.

Overhydration Scenario

You’re running Run the Red 120k  in Wyoming. The course is gorgeous and the temperatures are in the low 70s Fahrenheit (low 20s Celsius). Gels upset your stomach during your last race, so this time, you’re planning to use a sports drink for your calories. You put 100 calories of drink mix in each of your 500-milliliter hydration flasks. Your plan is to take in 200 calories per hour. You’ve trained through the summer down in San Antonio, Texas (95 to 100 Fahrenheit or 35 to 38 Celsius) using this method, with great success.

Six hours into the race, you’ve got a mild headache, you’re nauseated, your fingers are swollen, and your watch feels tight on your wrist. Your shorts are also tight at the waist. You feel wrecked. You make it to the mile-30 aid station and share your woes with your crew.

Your crew thinks you’re dehydrated. Before they give you anything to drink, what can they ask to be sure you’re actually dehydrated?

They should ask, “Are you thirsty?”

You are not, so it’s not dehydration that’s causing you to feel so rotten.

What combination of questions could your crew ask to help them determine whether you’re overhydrated?

  • “How much have you been drinking every hour?”
  • “Have you urinated?”
  • “Do you feel bloated or swollen? Do your clothes feel tight?”

You answer:

  • You’ve been drinking one liter/hour for the past six hours.
  • You have not urinated since you started running.
  • Yes, your hands and wrists are swollen. Your shorts feel tight around the waist.

You’re showing classic signs and symptoms of mild to moderate overhydration.

Signs and Symptoms of Mild/Moderate Overhydration 

  • History of heavy water intake usually over four or more hours
  • Headache
  • Unusual weakness and fatigue
  • Swelling and bloating
  • Nausea and/or vomiting

Your friends tell you need to stop drinking until you start peeing again. They load you up with a peanut butter and jelly sandwich for calories and tell you they’ll meet you at the next aid station in seven miles.

You try to eat the peanut butter and jelly sandwich, but you just can’t stomach it. After a mile, you decide to go back to using the calories in your hydration flasks. By the time you get to the next aid station, you’re clearly disoriented. You’re convinced you’re at the finish line and you’re talking about getting into your car to get back to the Lander Bar.

Mental-status changes (confusion, disorientation, combativeness, or unconsciousness) signal how severe your overhydration is. Your brain is swelling. You need medical attention immediately.

Your crew asks for help from the aid-station volunteers. They’ve all taken a Wilderness First Aid class and know that severe overhydration (hyponatremia) like this requires rapid evacuation.

At the hospital, they carefully restrict fluids while adding salt to draw the fluid from your brain. You make a full recovery and are released later that day. You vow to return to Wyoming’s Red Desert next year.

Overhydration Key Take-Home Points

  • Cause: Drinking too much fluid
  • Treatment: Stop drinking
  • Prevention: Use thirst to guide hydration

[Author’s Note: Learn more about caring for overhydration and other wilderness first-aid skills with a two-day NOLS course. Thank you to Tod Schimelpfenig, NOLS Wilderness Medicine’s Curriculum Director and author of NOLS Wilderness Medicine, for his guidance and oversight of this series. Thanks also to graphic artist Brendan Leonard, the trail and ultrarunner of Semi-Rad fame, for his graphics collaboration in this article series.]

Call for Comments (from Meghan)

  • Were you taught at some point in the past to drink a certain amount of fluids per hour during long runs and races? Now that scientific understanding of hydration and overhydration has evolved and the recommendation is for us to drink only when we are thirsty, have you shifted your fluid intake? Does it work for you to drink when you are thirsty and stop when you aren’t?
  • Have you experienced or seen symptoms of mild to moderate overhydration? What were the circumstances in which they came about?
Liza Howard

is a longtime ultrarunner who lives in San Antonio, Texas. She teaches for NOLS Wilderness Medicine, coaches, directs the non-profit Band of Runners, and drives her kids around in a minivan.

There are 18 comments

  1. Sarah Lavender Smith

    Thank you Liza for a really informative & important article. I’ve suffered from overhydration, and fingers as fat as sausages and an inability to pee, during 100Ks & 100Ms. I finally figured out that chugging soda was a big culprit. I’d drink water from my hydration vest fairly normally out on the route, then over-indulge in Coke or ginger ale at aid stations because it tasted so good and seemed like a good way to get calories (but soda has little if any sodium). Meanwhile I would go for hours without peeing even though I was puffy. I solved the problem by more carefully using “the spit test” (drinking when my mouth feels dry and it’s hard to form spit), using sports drink with electrolytes (GU Rocktane summit tea) rather than soda during the day for sugar/electrolyte/fluid combo in the hot, dry daytime of ultras, and saving soda as a special treat after sundown.

  2. Liza

    Thanks, Sarah! That’s really interesting about the soda. I like the spit test. I’m going to steal that. :) For me, overhydration is like hypothermia. The colder you get the dumber you get. The more overhydrated I make myself, the dumber I get about it — and the more I just keep drinking.

  3. Gordon

    I wonder if the liquids consumed that contributes towards overhydration perhaps tend to contain not enough sodium or potassium even though the volumes consumed seems reasonable to replace fluid loss through sweat, etc. The World Health Organization’s oral replacement solutions contain a considerable amount of salt, much more than sugary sports drinks. I think the use of NSAIDs like ibuprofen or naproxen doesn’t help the kidneys function as optimally as they need to on long runs.

  4. Liza

    Gordon, from what I understand about exercise-associated hyponatremia (EAH), it is not a salt loss issue at all. We’re just diluting our blood by taking in too much fluid. The amount of salt in our bloodstream doesn’t really change; Our blood’s “less salty” because we added so much water to it.
    Sports drinks or oral replacement therapy can still cause overhydration because the electrolytes and sugar in them don’t alter that they’re mostly water.
    Let me know if that brings up other questions for you.

  5. Cary Stephens

    The book Waterlogged by Timothy Noakes endorses Liza’s message here–“Drink to Thirst.” Given the dangers of overhydration, drink to thirst is clearly the first message to deliver to the public on this topic. However, defining “thirst” is a tricky thing in endurance exercise. Is it, “water tastes good so I should keep drinking,” or is it, “Oh my god, I have to find water now or I am going to die.” For most, it is probably somewhere in between. However, some, like me, have no strong sense of thirst while running. It seems to be masked by other senses (or often nausea), even when I am down 8% of my body weight mid-race. So, while “drink to thirst” should be the first approach taken, if it consistently leaves you dehydrated to a point that impacts performance, wouldn’t tracking your sweat rate at various temperatures and then devising a reasonable (and conservative) hydration plan applicable the race/training day conditions be an approach to consider?

    1. Liza

      Definitely, Cary. Like you said, most runners can rely on thirst. But what works for most, doesn’t work for all. I’d take your approach if that was my experience. Has it worked well for you?

      1. Cary Stephens

        Not perfectly well, especially as the distance increases. More than you want to know, but I am one of those people who suffers from chronic nausea as the runs/races get longer (used to be at 4 hours, now at 8 to 12 hours). Despite years of experimenting, I have never figured out the true cause (or causes). It is usually worse in the heat or elevation, with my weight typically down 5+%, so I suspected dehydration. When I have received IVs at the finish, the nausea vanishes, so that also pointed to dehydration, but last year I did a test run on a warm day (tracking everything) intentionally drinking to keep my weight loss at less than 5%. I still got nausea. It takes hours for the symptoms to abate, so I am now thinking (guessing really) that my kidneys may not process fast enough to keep up with toxins building up. They build up until I feel sick. When my kidneys catch up, I feel better. Looking for a specialist at this point.

  6. Tom Gamber

    I was thinking maybe I was dealing with this during my last 50k. It was a moderate day, temps in the 50’s. My fingers were swollen and I was feeling bloated in my stomach. However, I was very thirsty after the first 10 or so miles. I drank about 6 bottles of tailwind and one bottle of water through the entire race, (8HRs). In addition I used about 10 spring energy gels. I did chug some soda at the aid stations. However, I remained thirsty till the end. I peed maybe twice? Does this sounds like overhydrating?

    1. Liza

      Tom, if you were thirsty, I don’t think it was exercise-associated hyponatremia. It sounds like the salt you were taking might have caused your swelling and thirst. Sadly, it’s not just overhydrating that can make you swell up like a sausage. Figuring out what was going on would be easier if it was. Salt will cause you to retain fluid too. You might have just taken in more than you needed for those temps.

  7. Matt

    Great article. This happened to me once in a 100 miler about 3 years ago. I overhydrated throughout the hot day and then kept it up when the temps dropped at night. I was dizzy, delirious, and shaking badly. After they cut me from the race, I eventually threw up a lot of water. Then after sleeping for an hour my body finally began to urinate a full bladder about ever 15 minutes!! The signs were there by mile 35 but I didn’t know what they meant. My wrists had swollen so much that I had to loosen my watch band twice and take off my wedding ring. Since this experience I got educated and now drink to thirst with fairly low to moderate salt intake as needed. One thing I also discovered was that eating certain foods often – like PB&J – tended to make my mouth feel thirsty due to the consistency, even though I really wasn’t. I’m somewhat sensitive to salt anyway – HBP. So now when I eat these foods I try to rinse my mouth with water and spit it out so that I can regain my true sense of thirst. Thanks again for the amazing article!

  8. Liza

    Thanks so much, Matt! And thanks for sharing your race story. That’s really interesting about PB&J and other foods making you want to drink more. Makes sense.

  9. Melissa Trolene

    Fluid and electrolyte balance is so complex that nurses spend a few months learning about out it! Liza, what a phenomenal (and engaging format- I love the quiz style) article explaining some of the basic behind overhydration, myths and a few direct questions crew and runners can make to detect and how to treat it. I was starting ultra running in nursing school and I was amazed (and still sometimes am) that most of us make it off those courses alive and healthy.

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