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


Hyponatremia – low sodium levels – occurs when runners consume too much water. Most of the time, runners tend to suffer the opposite: dehydration.

But hyponatremia is a real thing runners can suffer from. Often this happens in large marathons where water stations are present every mile, making it easy to drink more water than your body needs.

In this article, we cover what to know about hyponatremia and how to prevent it.

What Is Hyponatremia?

Hyponatremia is the medical term for low levels of sodium in the blood. It can happen to runners, with research showing it’s the most common electrolyte disorder among endurance athletes.

We naturally have certain levels of certain electrolytes dissolved in the blood, which play important roles in almost every process in the body.

Sodium, in particular, helps regulate the body’s water content. But more importantly, it’s a crucial component of the body’s electrical impulse transmission system.

This means it’s a vital part of helping the heartbeat and nerve signals sent around the body. When your blood sodium levels are low, these important functions can start to go haywire.

What Causes Hyponatremia?

Several different factors can cause hyponatremia. For runners, it’s usually caused by drinking too much water, which dilutes the sodium levels in the blood to a dangerous level.

When sodium levels decrease, the membranes of the body’s cells become more permeable. This allows water to “leak” into the cells, which leads to multiple unpleasant and potentially fatal consequences.

Certain medical conditions can also make people more prone to hyponatremia. These include certain liver, kidney, and heart diseases and hormonal conditions. On the other hand, some medications can also lead to hyponatremia, like diuretics and some antidepressants.

In some cases, those with mental illnesses that compel them to drink may be prone to the condition. It can also happen in warm weather when people naturally drink more water but aren’t losing a lot of fluid through sweat.

Exercise-Associated Hyponatremia

Exercise-induced hyponatremia—also called exercise-associated hyponatremia or EAH—is a form of hyponatremia that often affects athletes. It can happen to anyone from beginners to experienced athletes if their hydration is not on point.

When performing high-intensity exercise or doing physical activity for extended periods, you lose electrolytes through your sweat and water. Runners who rehydrate with water but don’t replace electrolytes are at risk of hyponatremia, as their fluid levels increase, but their sodium levels continue to decrease.

Symptoms of Hyponatremia

Spotting the symptoms of hyponatremia as soon as possible is critical for effective treatment. If you’re concerned that you may be suffering from it, don’t try to push through—it can be life-threatening if not treated.

Early Symptoms to Look Out For

The first signs may be similar to dehydration. You might feel fatigued, have muscle cramps, experience light-headedness, or feel nauseous. It’s important to evaluate yourself if you feel these things to figure out what it could be.

If you haven’t been drinking enough, it’s likely to be dehydration. But if you HAVE been staying hydrated, consider whether or not you’ve replenished electrolytes and how long you’ve been exercising. This might help you determine if it’s likely hyponatremia or dehydration.

Another early sign, which is a sure sign that it’s NOT dehydration, is swelling of the hands and feet. This occurs as water pools in the cells, and it’s a clear sign that you need to stop and seek treatment.

Signs of Advanced Hyponatremia

Signs that the hyponatremia has progressed to more severe levels include headache, vomiting, and seizures. Make sure you stop exercising and get help before it gets to this point, as it can seriously damage the brain and body if left untreated.

Factors That Contribute to Hyponatremia in Runners

The chance of developing low sodium levels can be increased by certain factors, including:

Duration and Intensity of Your Run

You’ll naturally lose more fluid and electrolytes during a longer run. Adapt your hydration strategy if your run is going to be over an hour in duration, as this is where the sodium/fluid balance can start to become a problem.

Also, more intense exercise sessions can increase your sweat rate and make you feel like you need to drink more. In these cases, while you may be exercising for less than an hour, you might be losing more sodium than you realize and not topping it up with an electrolyte supplement.

Weather Conditions

Hot, humid, and windy conditions can increase your fluid loss, which might lead to runners overhydrating and inadvertently causing hyponatremia. On the other side, running in cold weather can cause you to overhydrate if you aren’t sweating a lot accidentally.

Underlying Medical Conditions

Certain medical conditions can cause you to drink more fluid than is normal. Diabetes, for example, is a condition that may present with extreme thirst as a symptom. This can easily lead to unbalanced sodium levels if you aren’t careful, especially if you aren’t paying attention to your diet.

Signs That You May Have Hyponatremia While Running

If you experience any of these signs and symptoms during your run, it’s best to stop and seek some kind of medical treatment.

  • Swelling: This is the most alarming sign of hyponatremia. Your hands and feet can suddenly swell to more than twice their normal size.
  • Weakness: A feeling of weakness, unusual fatigue, or suddenly tired or physically exhausted earlier in your run than you should feel.
  • Pale Skin: Circulation can be affected, making the skin noticeably paler than it usually is.
  • Unusually Frequent Urination: If you’re stopping to relieve yourself more often than usual during your run, your body may be unable to regulate its own fluid levels.

Should You Be Worried About Hyponatremia?

Imbalances in the body can have much more severe consequences than you may realize. However, if you’re taking steps to ensure it doesn’t happen, you shouldn’t worry.

If you experience the early symptoms of hyponatremia, you can manage it by rectifying your hydration and consuming sodium to get that balance back to normal. Most athletes recover fully from hyponatremia with the help of a medical professional and a proper hydration strategy.

However, if you start developing severe hyponatremia symptoms, it’s time to worry. Medical attention is required, and you should stop running immediately and take steps to bring that balance back into harmony.

Continuing in this state could permanently damage the brain and organs, or worse, it could be fatal. Don’t let this deter you from running, though—it’s only something to worry about if you aren’t paying attention to your hydration.

What Should You Do if You Have Hyponatremia While Running?

If you recognize the signs while you’re running, don’t ignore them! Here’s what you should do when you experience symptoms of hyponatremia while running.

Stop Running and Seek Medical Help

We know… It’s tempting to just carry on running and hope it will get better. However, it’s in your best interest to stop and seek medical attention, because if left untreated, the symptoms can worsen and result in severe damage to the brain and body.

It’s up to you how you find medical help. We advise not driving to a hospital in this state, so you can call an ambulance if you have capacity. Hyponatremia can be a medical emergency, so it’s a good idea to get ahead of this as quickly as you can.

Consume a Balanced Electrolyte Solution

Once you’ve stopped running and you’re waiting for medical help, consume an electrolyte solution. An electrolyte tablet is good here, but try to take it in as little water as possible and as quickly as possible. Alternatively, eat a salty snack like pretzels, although an electrolyte solution will work a little faster.

Gradually Reduce Fluid Intake

Although it’s tempting to keep drinking, you want to reduce your fluid intake at this point to allow the levels of sodium and water to balance out again. If you take an electrolyte solution or eat a salty snack and then keep drinking, you’re not allowing your body to balance those levels out.

Tips to Prevent Hyponatremia

Ultimately, the best way to handle hyponatremia is to prevent it from happening in the first place! Here are our most practical tips for never reaching that point.

Know Your Sweat Rate

Calculating your sweat rate will help you to know exactly how much water you need to drink during a run. Once you have a number, sticking to it should help you avoid going overboard and potentially skewing your electrolyte balance.

To calculate it, weigh yourself before your run and after your run in the nude. Figure out how much weight you lost in pounds, and convert it to ounces by multiplying it by 16. Then, add the number of ounces of fluid you drank during your run. Lastly, divide the resulting number by how many hours you ran for.

It’s a good idea to perform this experiment in cold weather, normal weather, and in hot weather. This way, you’ll know how your fluid loss changes depending on the season and weather.

Plan Your Hydration for Your Entire Run

Once you know your sweat rate, planning your hydration for each run is a good idea. Try to take just the right amount of water so you don’t end up drinking too much without even realizing it.

By planning your hydration, you know exactly how much to drink, when to drink, and how to adapt when the weather changes. Also, it’s a good idea to set some reminders on your watch to remind you when to drink… And stick to it!

Short Run (Under 1 Hour)

You can get away with not drinking during this run, although it depends on your personal level of comfort. You only need a minimal amount of water if you want to drink, so a few sips from a bottle every few minutes should suffice.

Long Run (Over 1 Hour)

Runs over an hour long typically require an electrolyte supplement to prevent those levels from getting too low. You WILL need water for this length of run, and we highly recommend taking a few electrolyte tablets with you.

Take your first one around 40 to 45 minutes into your run. From there, you can take another one every hour to ensure your sodium levels aren’t dropping too low.

Be Mindful of Environmental Conditions

Your environment makes a difference as well. Heat, cold, and wind can affect your sweat rate, so calculate these upfront and adapt to them depending on the weather during each run.

Hot Weather and Wind

You will sweat more in hot weather, which means you’ll be losing more fluid than you might normally. In hot weather, you might be tempted to drink excessively to make sure you stay hydrated but take caution.

If you’ve calculated your sweat rate in hot weather, take the right amount of water with you on a run. Electrolytes will play an important role in warm weather, too, so make sure you take enough with you for the duration of your run—take one tablet every hour or so.

You may also dehydrate faster in windy weather, so your sweat rate may change. You should drink a little more, but do not go too far overboard from your sweat rate.

Cold Weather

You won’t sweat as much in cold weather, so you may need less water. You’ll still need to drink, especially on longer runs, but do not drink too much if your body isn’t losing much fluid.

As mentioned, it’s also a great idea to perform the sweat rate test in cold weather. Once you have a number, you can stick to that amount of water and know you’ll be fairly accurate and won’t overhydrate.

Remember that just because you aren’t sweating much doesn’t mean your electrolyte balance is staying just right. When you’re constantly drinking water but losing none, you’re still diluting those sodium levels, so continue using electrolyte tablets in cold weather.

Eat a Balanced Diet

If you eat a healthy, balanced diet, your body’s electrolytes should balance themselves out naturally. Keep in mind that if you’ve been eating badly, it will take a few weeks for your body to adapt to a healthy diet and new levels of nutrients.

Pay Attention to the Color of Your Urine

If you’re over-hydrated, your urine will be almost clear. It should be light yellow, indicating a good water and waste product balance. Too clear means there’s too much water in your system, and it’s leading to an imbalance. Take steps once you spot this and you can avoid worse consequences.

Know Your Body

So many runners don’t actually know their own body well! Pay attention to how your body responds when you drink too little versus too much when you use an electrolyte tablet versus when you don’t, when you hydrate according to your sweat rate, and when you just wing it.

When you know how your body feels when everything is good, it’s easier to feel it when things aren’t right. And when you feel that things aren’t right, you’ll be able to stop making mistakes that could cause injury or illness.

Photo of author


Ben is an avid road and trail runner, and has completed multiple marathons and ultras. A former running store owner, he now shares his knowledge and experience writing these articles.