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What You Should Know About Hyponatremia

BY William Ritter

Water is key to performance, but it turns out you can have too much of a good thing.

I started running in 1996. This was the same time that the ACSM (American College of Sports Medicine) came out with this journal article encouraging athletes to drink as much water as they can reasonably tolerate. This advice is probably the reason that to this day I still drink water frequently and carry a water bottle with me nearly everywhere.  

These days I’m definitely more relaxed about my water consumption than I used to be. ACSM had guided that athletes should drink at least as much fluid as they lose but the last time they updated this guidance was in 2007. In the wake of data and information discovered in the advanced research done since then by sport scientists such as Tim Noakes, author of Waterlogged and The Lore of Running; as well as Asker Jeukendrup of MySportScience and Andy Blow of Precision Hydration, we now know so much more than we did back then.

As we hit the official start of Summer, hydration generally becomes more important. Warmer temperatures mean more sweat, which means you need to consume more water to keep performing at your best. But taken too far, over-hydrating can be debilitating and even dangerous. Here’s what to look for.

What is Hyponatremia?

To start, let’s put a name to the condition that competes with our optimal performance in the heat: hyponatremia. Hypo, meaning low. Natremia, meaning blood sodium. Hyponatremia is what happens when the blood sodium levels become too low in the intracellular space. 

  • Normal ranges for blood sodium levels are between 135-145 mmol/L. 
  • Hyponatremia results when our blood sodium levels drop below 135 mmol/L. 
  • Hypernatremia would occur when our blood sodium levels are above 145 mmol/L. 

Causes of Hyponatremia

The primary cause of hyponatremia is when people take in too much fluid and their bodily fluids become hypotonic, meaning there isn’t enough sodium. Other causes include excessive vomiting or diarrhea, kidney disease (which can cause the body to expel too much sodium), and certain medications.

Symptoms of Hyponatremia

The symptoms of hyponatremia can sometimes be hard to detect. In its early stages, it could feel like nausea, cramps, or just a lethargic feeling; all symptoms similar to dehydration or regular race fatigue. In more serious cases, excess fluid is pushed out of the blood vessels and into the cells, causing puffy fingers and ankles—picture the edema experienced by many athletes at the end of an endurance event. Extreme hyponatremia can begin to affect the brain, resulting in seizures, coma, or even death.

Of course, the simple solution is to not drink too much. In fact, Tim Noakes has suggested that you should really just drink according to your thirst.  This may work for relative short course events < 2-4 hours. For longer events > 2-4+ a hydration plan would be advised. 


Between 2005 and 2013 there was a study conducted of finishers of the Frankfurt Ironman which confirmed that 10% of all the finishers were starting to become hyponatremic, meaning their blood sodium levels were about to be less than < 135 mmol/L or already were. Similar studies of participants in ultra runs found that over 50% of the participants were hyponatremic. 

Finally, a study in 2015 by Spanish researchers of 26 well-trained triathletes, had a placebo group and a salt tablet group. The triathletes were told just to drink as they wanted. They ingested 12 tablets at three different intervals during the 70.3 mile triathlon. The group that took the actual salt tablets finished notably faster. The placebo group finished in 5:33  +/- 40 minutes while the salt tablet group finished in 5:07 +/- 32 minutes. 


To avoid hyponatremia, it’s important to balance your fluid and sodium intake. A sweat test, which measures the volume and composition of your sweat, can help you better understand this balance. It’s also good to be aware of your risk factors when exercising in the heat, including compromised kidneys or medications that might inhibit your sodium levels. Hyponatremia can be a serious problem, but it doesn’t have to be a common one if you hydrate wisely.

About William Ritter

William Ritter, from Tyler, Texas, enjoys working with athletes that are looking to improve their performance in triathlon or running. Ritter’s coaching is detailed and based on the individual athlete, blending the art and science of coaching. He is the Head Coach at Fly Tri Racing and holds many certifications, including TrainingPeaks Level 2 and Power Certified Coach, Ironman U, Tri Sutto Coaching Certified, USA Triathlon, USA Cycling, USA Track and Field Level 2 Endurance Certified Coach and USATF Cross Country Specialist. To learn more about Ritter and personal coaching, visit Fly Tri Racing or send an email to flytriracing@gmail.com.


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