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Battling Exercise Associated Hyponatremia – Are You At Risk?

As the popularity of long endurance events grows, and the science of hydration expands, the main hydration concern seems to be moving slowly away from typical dehydration (excessive fluid loss) and onto exercise associated hyponatrmeia (which I will now refer to from this point on as EAH in order to prevent my hands from cramping).

What is EAH? The medical definition is blood sodium levels below 135 mmol. Normal levels are accepted to be 135-145 mmol, so you can see there can be differing degrees of EAH. My goal is to keep this pretty straight forward so I’ll spare you with all the really detailed sciencey bits and numbers.

How does this typically happen? Generally speaking, most endurance athletes get EAH from consuming too much water, which dilutes the total sodium in their body. But at the same time, this can also happen by having high net sodium losses and consuming sports drinks that are a much lower concentration than your sweat. You are basically running a sodium deficit long enough to throw off the balance in the blood stream. For example, if you are losing 1000 mg/L in your sweat (which is average based on our testing), sweating 1L per hour (a fairly modest sweat rate for heat acclimated athletes), but drinking one L of fluid that only contains 500 mg of sodium (that’s generous for big brand drinks) in that same hour, you are net -500 mg in that hour even though your net fluid gain/loss was zero. That may not catch up with you in one, two, or maybe even three hours, but sweat losses are not a constant and the average person can only absorb about 1L of fluid an hour. Play with the math and you can see how the net sodium losses can easily add up!

Why is sodium so dang important? I know. You’ve heard for years how bad sodium is for you. In excess, anything is bad for you. Water included. Hell, too much oxygen can kill you. Sodium is the predominant electrolyte in your extracellular fluid. It carries an electrical charge that helps pass impulses to the nerves, telling muscles and organs to do their damn job. Even more importantly sodium helps maintain proper fluid (and ultimately blood) levels in the body. Not to mention aiding in a number of organ processes like digestion.

What are the symptoms of Mild EAH? Once your sodium levels drop below 135 mmol, you will likely still have normal vitals (which is why it’s often misdiagnosed), but you may experience things like light headedness, nausea, cramping, and possibly even weight gain. These are not performance enhancing symptoms by any means.

The scary bit. What are the symptoms of severe EAH? Not trying to scare you, but there have been a few confirmed deaths in the last few decades due to EAH, including one at Ironman Frankfurt in 2015. See, once your blood sodium levels are really low (meaning too much water in the blood), your body will shift water from the extracellular fluid to intracellular compartments to attempt to balance everything back out. This causes swelling in the brain that can ultimately cause a herniation of the brain stem, or other brain damage. Not good at all. The less scary symptoms include severe cramping (the total body kind), headaches, vomiting, an altered mental state, heart arrhythmias, seizures…do I even need to keep going?

Who is most at risk for EAH? Here’s what you really came to find out. Are you at risk? Well in the right (or wrong) conditions, any athlete can be at risk. But here are a few groups who could be more at risk than others:

  1. Salty Sweaters – I put this one first because I am a member of the SSC (Salty Sweaters Club). I am also a recovered chronic receiver of EAH. You want to know why we got so involved in hydration science? It was me and my long standing issues. With a high sweat sodium concentration (1453 mg/L), and a high sweat rate (I’ve seen 3L per hour in extreme heat), my net sodium losses were so high I could barely finish an hour race without feeling like death. I’ve been symptom free for a while now thanks to our Precision Hydration testing and the strongest sports drink on the market, PH1500.
  2. Slower Athletes – I’m not taking jabs here. It’s just a fact that the longer you are out there, the more time you have to produce massive fluid turnover OR drink way too much water.
  3. Smaller Athletes – This is contrary to popular belief. But the fact is smaller athletes have less total body water. With less water, you have less room for fluctuations in sodium and total body water. Some theorize this is why we’ve seen more issues with kids in the extreme heat over the last decade or two, but there is little data on EAH in adolescence.  As we’ve said before, sweat sodium concentration is completely individualized (genetic) and doesn’t care how big or small you are. Sweat rate is slightly higher on average in bigger people but it can still be vastly different in similar athletes. We’ve tested men that lose 450 mg/L and women who lose 1600 mg/L. We have petite lady athletes who sweat 2.5L per hour and big burly dudes who sweat less than 1L per hour in similar climates.
  4. Those on Certain Medications – If you are taking medication, even things like NSAIDS, it may impair water clearance from the body. I won’t dive into this too much because I am no doctor. However, it may be worth talking to your doctor if you are on medication to check and see if it could affect your kidney function.
  5. Newbies – A lot of newer athletes don’t have a lot of experience with proper hydration, let alone honing their thirst response. On top of that, it’s not uncommon for a newer athlete (and even seasoned vets) to get wrapped up in the event experience and totally ignore what and how much they are drinking. Been there, cramped after that.

How do I protect myself from this dreaded acronym?

As bad as it sounds, EAH isn’t all that tough to combat with the right approach. Here are our recommendations for staying hydrated and keeping your electrolytes in proper balance.

  1. Have a plan. Any plan is better than no plan at all. You don’t have to force yourself to drink when you are not thirsty, and you don’t have to hit the bullseye per se, but you will want an idea of what you are personally losing fluid and electrolyte wise in similar conditions to your next event, race, or workout. The important thing is, the longer you are out there, the closer you will want to be to covering your fluid/sodium outputs. If you want to ballpark your sodium needs, take Precision Hydration’s free online sweat assessment. If you want to be told exactly what you are personally losing, and talk it over with one of our sweat experts, book a Precision Hydration test with us at your convenience. For more info on PH testing, check this out.
  2. Drink to thirst…..most of the time. Again, if you are newer to endurance sports you may not have a handle on when and how much you need to drink. Also, it’s been shown that aging individuals experience a diminished thirst responses over time. Kids are in the same boat as most newbies. The DTT approach also loses a little luster when we are talking about exercise lasting more than 2-3 hours. But for a lot of athletes, as long as your fluids are concentrated close to what you need based on your sweat sodium output, drinking to thirst is generally fine. We encourage our athletes to consistently test their sweat rate, especially leading into an important event. That way we can make some adjustments in electrolyte or fluid volume, especially if we are seeing a big difference in intake versus output.
  3. Preload. This has had a major impact on the athletes who have added it to their routine. Preloading is simply topping off your sodium stores prior to exercise with high sweat losses. It basically builds a buffer by raising sodium levels right before exercise. It also helps bring more fluids into the blood which means more fresh blood to the muscles, and more blood to cool your body. Preloading is generally done 90-120 minutes before exercise, with fluids of concentration greater than or equal to 1000 mg/L. 16-32oz is sufficient, and the body will get rid of what it doesn’t need (yay for more time in a port-o-potty). Most of our athletes use the Precision Hydration H2Pro 1500 (1500 mg/L) for preloading.

There you have it. As scary as EAH can sound, it’s not a big deal with the right approach. If you have any questions for us, don’t be afraid to contact us or click the intercom in the bottom right of the screen.

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