Skip to main content

Hyponatremia: What It Is and How to Prevent It

Boston Marathon 2011

Boston Marathon 2011

All you marathoners and triathletes out there: Have you ever heard of the term hyponatremia? If you haven’t, then you should familiarize yourself with this potentially life-threatening condition. A little education can go a long way.

While statistics on this are hard to come by, there have been a few much-publicized cases of this condition that have resulted in the very unfortunate death of the athletes. Deaths from hyponatremia occurred at the 1998 Chicago marathon, the 2002 Boston and Marine Corps marathons, and also at the 2007 London marathon. Testing done on approximately 500 athletes following the 2002 Boston Marathon showed that thirteen percent of those tested had hyponatremia, a fairly alarming figure.

What Is Hyponatremia?

So what exactly is hyponatremia? Hyponatremia is a metabolic condition in which there is not enough sodium (salt) in the body fluids outside the cells. When the amount of sodium in fluids outside cells drops, water will move into the cells in an attempt to balance the sodium levels. This, in turn, causes the cells to swell with too much water.

Although most cells can handle the swelling, brain cells cannot because they are confined by the skull. It is this brain swelling that causes most of the symptoms of hyponatremia.

The accepted scientific definition of hyponatremia is when there are less than 135 millimoles (unit of measurement used to express the amount of a chemical substance) of sodium per liter of plasma. Normal values range from 138 to 142 millimoles, and symptoms usually begin when values fall below 130. If the plasma sodium level falls below 120, there will be massive brain swelling, and the condition can be fatal.

Long-distance athletes, marathoners, and triathletes are the athletes who are most at risk because the longer they exercise, the more they sweat, and the more likely they are to drink too much water without taking in enough sodium. Most athletes don’t get into trouble with a short workout.

It is longer races, such as the marathon or an Ironman Triathlon, where people get into trouble simply because of the extended time that they are out there. Being on the course longer requires the intake of important nutrients to replace what has been expended through sweating. Being told to drink water at every water stop, while sounding like good advice, may lead athletes to this condition.

There are two basic causes of hyponatremia, consuming too much fluid over too short a time span and excessive sodium loss through bodily sweat. If both factors are present, the risk is increased. If you are one who sweats at a high rate, then your risk is also higher; however, excessive fluid intake for a normal sweat rate can also lead to inadequate sodium levels and, therefore hyponatremia as well. If a person is over-drinking, meaning that they are not using the amount of water they are consuming for their level of exertion, they will dilute their plasma-sodium concentration and be more prone to the condition.

Early indications that you may be hyponatremic include disorientation, feeling bloated, nausea and vomiting. High blood pressure and headache often come next. In the more severe cases, respiratory distress and seizures can occur, and the most advanced stages include coma and possible death. Another very specific indicator of hyponatremia is weight gain during a race or long run. Most of us don’t stop to weigh ourselves during a run, but studies have found that weight gain during a run due to excessive drinking and water retention is the strongest indicator of hyponatremia.

Water anyone?

Water anyone?


How do you prevent hyponatremia? For starters, you need to become more aware of your fluid intake and your rate of perspiration. During training runs, start to notice how your body reacts to varying amounts of fluid and salt intake. Consume snacks with salt such as chips or pretzels and use sports drinks that have sodium and potassium in addition to water. On race day or prior to a long run make sure you eat a good breakfast and bring a snack with you to eat 30 to 60 minutes before the race starts.

Keep in mind also that the weather plays an important part in your rate of perspiration. In addition to making sure that you are not overdoing your fluid intake, you need to also stay alert to dehydration if you don’t drink enough. The fear with the competitive mind is that we sometimes overdue everything, so this is certainly a case where you need to maintain a proper balance.

It is also a good idea to make sure your supporters and family are aware of this condition as it may be impossible for you to communicate this to them should you have a problem. For most of you, this may have never been nor ever will be a problem. However, if you have been running for a number of years you may be able to recall a run or two, or perhaps even a race where you had some of these symptoms.

I have been running for over 40 years now, and I can think of a few particular cases where I certainly may have had this condition. It’s a little scary now to think that my reaction to these symptoms back then may have been to simply drink more water because that’s what we did to avoid dehydration. Back in the 1970s and 1980s, who knew that you could literally drown yourself from drinking too much water while running?

So, the lesson to be learned here is that too much of a good thing can certainly be bad for you. During long runs or races, you should drink to minimize your weight loss, but don’t over drink. Add in sports drinks that contain sodium and potassium. In the days leading up to a race or long run snack on salty foods? During your training, develop a feel for how your body reacts to what you are putting into it. Just a little precaution can go a long way toward avoiding this potentially serious condition.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2012 Bill De Giulio


Bill De Giulio (author) from Massachusetts on June 11, 2013:

Hi Mary. Thank you. In my youth I had no idea about this and had never heard of it until a few high profile unfortunate deaths at some of the larger marathons. Today the folks who organize races are all too familiar with this condition and warn competitors about it. It's all about being educated and aware of the possible risks. Thanks so much for stopping by today. Have a great day.

Bill De Giulio (author) from Massachusetts on June 11, 2013:

Hi pinto2011. Thank you for taking the time to read and comment. I sure wish I knew about this 30 years ago. For those today just getting into a running program they should be aware of what this is and how to recognize the symptoms.

Bill De Giulio (author) from Massachusetts on June 11, 2013:

Hi FlourishAnyway. Thank you for helping to spread the word and raise awareness. In my youth I am certain that I experienced this but had no idea what it was. Back then the solution was to drink more water, which is the worst thing you can do. Thanks for the visit and have a great day.

Bill De Giulio (author) from Massachusetts on June 11, 2013:

Hi Meg. So sorry to hear that your sister-in-law was diagnosed with this. It can be life threatening. I am glad to hear that she is being treated and hopefully is recovering. Thanks so much for adding a very important comment here, that you don't have to be a runner to experience this.

Mary Craig from New York on June 11, 2013:

Evidently this is something we should all know about but don't! What a greatly informative hub Bill. Perhaps you may even save a life with this. Low sodium is not something most people think of, unless they are in the tropics. Well done and a service to all.

Voted up, useful, and interesting.

Subhas from New Delhi, India on June 11, 2013:

Hi bdegiulio! Very nice and wholesome insight into this topic. Will really help newbie runners.

FlourishAnyway from USA on June 11, 2013:

Sending this to my triathalon/marathon husband and his friends. Thanks for writing about it.

DreamerMeg from Northern Ireland on June 11, 2013:

This is not only a problem for marathoners. My elderly sister in law was diagnosed with this. She had been told to lower her salt intake and just cut it out all together! She was becoming confused and this wasn't helped by being prescribed a diuretic tablet by her doctor to remove fluid from her body (to lower her blood pressure). Following a fall, where she broke a bone in her elbow, blood tests were taken to show she was suffering from hyponatraemia and low potassium. She is having to take tablets to counter this and her confusion is lifting and her health also improving.

Bill De Giulio (author) from Massachusetts on June 11, 2013:

Hey rajan. 30 years ago no one knew of this condition. Today race organizers are very much aware of this as there has unfortunately been a few deaths due to this. Thank you as always for the read, comment, vote, share, pin, etc.... Have a great day.

Rajan Singh Jolly from From Mumbai, presently in Jalandhar, INDIA. on June 11, 2013:

I had no idea of this condition, Bill. Thanks for adding to my knowledge. This is a must read for the serious runner.

Voted up, useful, interesting. Shared and pinned as well.

Bill De Giulio (author) from Massachusetts on March 25, 2013:

Hi Michelle. Thanks and glad you found the hub useful and informative. Have a great day.

Bill De Giulio (author) from Massachusetts on March 25, 2013:

Hi Peggy. Amazing how years ago no one really seemed to know about these things but hyponatremia can be very dangerous. Thanks for stopping by and the vote, share, etc.

Michelle Clairday from Arkansas on March 24, 2013:

Very informative. Thanks for the useful information.

Peggy Woods from Houston, Texas on March 24, 2013:

It sounds like you have experience in this area. There are so many sports drinks available now and other advice that if marathoners and triathletes pay attention, hopefully they will not suffer the results of hyponatremia. Up and useful votes and will also share.

Teresa Schultz from East London, in South Africa on May 19, 2012:

Thanks for the reply - I think perhaps I'll (try to) start only worrying about this more when and if my boys do longer races in the future, although it's nice to be able to give them some guidelines now already, so that by the time they're running longer races they are already used to being able to properly gauge how much they need to drink before during and after a race, and what exactly they need to drink. Although it's a pain that running could never be done without any risk or danger or injuries, it's certainly interesting learning about all the things that could (and often do) go wrong. Your hubs are very informative. Keep up the good work.

Bill De Giulio (author) from Massachusetts on May 19, 2012:

Hi Teresa. The key is to be hydrated which means not too much and not too little. For a 10K hyponatremia should not be a problem. The longer the distance the more you need to be concerned about this, especially at the marathon distance. For these longer distances, runners really should be using something that is replacing the sodium that they are losing through the sweating process. I'm sure your boys will be fine but it's always good to know about these things. Thanks for being a concerned mother and for stopping by.

Teresa Schultz from East London, in South Africa on May 19, 2012:

Oh dear - something else to worry about for an over-protective mother (me) when my boys are running races. I panic about dehydration because the boys tend to think they only need to drink if they're feeling thirsty during a race, and my eldest son even teases me that he thinks it would be fine to run a 10km or 15km race and only drink at the end of the race. It's just to get a reaction out of me though :) as he does still drink at the water stops during the race. Often the 10km races in South Africa only have water stops, while the 15km have a weak diluted (I think) energy drink, and the 21.1 km and up usually offer flattish cola too.

Now I'll be telling my sons drink, but not too much. I'm pleased your hub has alerted me to the dangers of drinking too much - thanks.

Bill De Giulio (author) from Massachusetts on April 18, 2012:

Thanks Rema. Appreciate the comments and sharing. If you're an athlete you should know what this condition is and be aware of the signs. Just a little knowledge could go a long way. Thanks for sharing.

Rema T V from Chennai, India on April 18, 2012:

Very informative and well-written hub. Just the kind of info that every sportsperson and others too should read and understand. Socially shared.



Bill De Giulio (author) from Massachusetts on April 06, 2012:

Thanks Nicole, glad it helped. Appreciate the comment.

Nicole S Hanson from Minnesota on April 06, 2012:

I learned a lot here, thank you!

Bill De Giulio (author) from Massachusetts on April 03, 2012:

I've heard of this event, the name says it all. Sunflower seeds were a good choice for the salt. Appreciate the comments.

Judy Specht from California on April 02, 2012:

Last summer rode the Hotter'n Hell Hundred in Texas. My friend and I found that we could go 30 minutes before we started to go numb. We started hydrating two weeks before the ride and ate sunflower seeds on the drive from California to Texas. Couldn't get enough salt.

Every athlete should read this hub.