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Hyponatremia And Running – What Is It And Should You Be Worried?

We’ve all heard of hypothermia, but have you ever heard of hyponatremia? Just like hypothermia means that you’re too cold, hyponatremia means that you don’t have enough sodium in your blood.

As runners, it’s important to stay healthy and have just the right amount of fluid and sodium in our systems. In this article, we’ll discuss hyponatremia in runners, covering everything that you need to know about it, including how to prevent it and put your worries aside.

What is Hyponatremia?

As I hinted at before, hyponatremia means low blood sodium. It means that you have too much water and not enough sodium in your body. Although too much sodium in your body is bad, you do need the proper balance of water and sodium to stay healthy.

Hyponatremia occurs when these are imbalanced, and you have a salt deficiency. As runners know, having enough salt (and electrolytes) in your body is key to running well, so hyponatremia is definitely a big deal if you don’t get it fixed.

What Happens If You Develop Hyponatremia?

While it typically resolves itself within a couple days to weeks, hyponatremia will lead to symptoms like confusion, fatigue, headaches, and nausea, leaving you pretty uncomfortable. Although it’s not the same as dehydration, the symptoms can be fairly similar.

You might be more restless or irritable than usual, and you’re likely going to have less energy and be more drowsy. More serious symptoms include muscle weakness, spasms, or cramps, seizures, and even a coma.

If you experience any serious symptoms, you will want to call a medical professional immediately. If it’s something less serious, you probably will be good just getting some more sodium into your system.

If your sodium level is extremely low, it leads to rapid and dangerous swelling of the brain, which can cause death. 

While fatal hyponatremia is rare, it has occurred in long distance runners and military recruits. I knew someone who was training to join the military and who wanted to stay hydrated, but drank too much water, leading to low sodium levels and ultimately his death.

When Are Runners Likely to Develop Hyponatremia?

Typically hyponatremia occurs in runners when there is prolonged exercise, meaning that you’ve likely sweat all of the sodium out of your body. However, it can also occur if you drink too much fluid too quickly.

Some studies found that over 30% of runners who participate in long distance events like marathons and ironman triathlons experienced hyponatremia. That’s ⅓ of all the athletes tested, so you should definitely not rule yourself out if you participate in prolonged exercise.

What Types of Runners Are Most at Risk of Hyponatremia?

If you are a long distance runner, especially an ultramarathoner, you are more at risk of hyponatremia than shorter distance runners because you’re spending more time sweating and therefore losing salt. It’s therefore very important that you replenish those stores.

Additionally, runners who may be more worried about becoming dehydrated and regularly drink more fluid (particularly without electrolytes) than they lose in sweat are also at a greater risk of hyponatremia.

If you are a slower runner, if you have a smaller body, or if you sweat a lot (especially a salty sweat), you are also a more likely candidate to suffer from hyponatremia because you’ll spend more time sweating, you need less fluid to dilute sodium levels with a smaller body, and you’re losing more sweat (and therefore sodium), respectively.

What Are Common Causes for Hyponatremia?

Unfortunately, hyponatremia can be caused by a wide variety of things, so depending on your physical condition and lifestyle, it could take some time to figure out what exactly is causing it.

Physical Changes in Your Body

If you have heart, kidney, or liver problems like congestive heart failure, fluids are more likely to accumulate in your body, meaning that your sodium levels will decrease because they are diluted.

Similarly, if you experience hormonal changes due to adrenal gland insufficiency (Addison’s disease) or have low levels of the thyroid hormone, you may be more likely to experience hyponatremia.

Chronic Vomiting/Diarrhea/Dehydration

If you have been dehydrated whether it’s due to severe vomiting and diarrhea or due to a diuretic like alcohol, your body will lose electrolytes, including sodium. This is especially bad if it’s just before a run when you lose even more electrolytes through sweating.

Intense Physical Activity

While it’s definitely important to stay hydrated as a runner, you don’t want to go too much the other way and drink too much water. Again, this is not good if it’s just before a run because you’ll lose electrolytes without replenishing them.

Additionally, continuous sweating for five hours or more like you would experience in a marathon or ultramarathon can lead to hyponatremia if you’re not also making sure to replace the sodium that you’ve lost.

Certain Types of Medication

Some medications get in the way of maintaining a good balance between water and sodium. This includes water pills, which are used to get rid of excess salt in the body, and some antidepressants and pain meds. 

How Do I Prevent Hyponatremia on Long Runs?

While hyponatremia is definitely something to be serious about, it is easily preventable if you are aware and make sure that you’re keeping things level.

Drink Enough

If you’re dehydrated, your body will have lower sodium levels to begin with, which is not good if you’re going on a long run. Make sure that you drink enough the day before going for a run and the hours leading up to your run to begin the run hydrated.

But remember. Don’t overdo it! A good rule of thumb is to drink half of your body weight in fluid ounces. If you’re drinking way more than that, it’s too much. Also, your urine should be a light yellow, not necessarily super clear. If it’s really, really clear, you might be drinking too much.

Drink Sports Drinks

Water is important to stay hydrated, but you also need electrolytes, which you’ll get through sports drinks as well. If you’re running a race, it’s okay if you take the water the majority of the time, but don’t forego the sports drink that will give you the electrolytes (and sodium) you need.

Ideally, you’ve thought about this ahead of time as to when you’re going to take water and when you’re going to take sports drinks. Some runners even like to carry two hydration bottles with them on long runs—one for water and one for a sports drink. 

Don’t Force Yourself to Drink

If you’re forcing yourself to drink water when you’re not thirsty and you know you’re hydrated, then you’re likely putting too much fluid into your system that will dilute your sodium levels.

If you’re not thirsty, don’t pressure yourself to drink a glass of water. Your body will tell you when it needs more fluid, so don’t stress.

Drink in Small Doses

As we mentioned above, sometimes hyponatremia can be caused by drinking too much too quickly, so avoid chugging your water. Instead, try to evenly space when you’re intaking fluid throughout your run (and your day). Take sips, not gulps.

Eat Salty Snacks

Typically during longer races, you’ll get offered pretzels some time during the race. This is because it’s a way for you to get some salt into your system that you’ve lost. Make sure that you eat some salty snacks after several hours of running and when you get back home too.

Figure Out Your Sweat Rate

Finally, the best way to help prevent hyponatremia is knowing your body through your sweat rate. You can calculate this by weighing yourself without clothing before a run, ideally running for an hour (to get your sweat rate per hour), drinking a measured amount during your run, and weighing yourself without clothing after you complete your run.

Camelbak has a handy datasheet that you can use to convert the numbers into your specific sweat rate and how much fluid you should be drinking prior to, during, and after your runs. 

It’s also important to remember that sweat rates can vary in different seasons and climates, so it might be worthwhile to calculate a couple times every year to make sure that you’re still getting the fluid that you need.


Hyponatremia is like hypothermia in that they are both serious issues that you want to avoid. Fortunately, making sure that your sodium and fluid levels stay balanced, especially if you’re a long distance runner, will ensure that you don’t have to deal with hyponatremia.

If you have a preexisting condition that makes you more likely to have low sodium levels, make sure that you see a doctor before starting a running program to ensure that you’re intaking the sodium that you need to stay healthy and balanced.

The Wired Runner