Summary: CAT Talk on Exercise Associated Hyponatremia

We were privileged to hear a talk from Dr. Mitchell Rosner on Exercise Associated Hyponatremia (EAH) this week. This is a condition where an athlete has low sodium levels in the blood during or after an endurance event. Some people may show little or no ill effects due to EAH, perhaps just some nausea; however, for others this can result in more severe nausea, confusion, seizures, and even death in some documented cases. It has become more common in the last 20-30 years as athletes are encouraged to hydrate liberally, without proper attention to keeping sodium levels up. Dr. Rosner covered some specific cases, causes, avoidance, detection, and treatment of EAH. While the cases were fascinating, I’m going to primarily summarize the causes and prevention of the condition, as that is what athletes have the most control over. Some of the data is from (at least) 2 years of analyzing Western States 100 mile runners.

– Simply put, don’t over hydrate. Drink 400-800 ml (14-27 oz) of fluid per hour max. Thinking in terms of a marathon, this is probably 4-6 ounces at each aid station for a typically laid out race (depending on your pace). For an ultra, this might be a typical handheld bottle per hour. Times between aid stations vary too much to even try to generalize consumption. More than that dilutes the sodium in your blood. Sports drinks don’t have enough sodium to provide much help, you’ll still be diluting. Drink to thirst. The recent advice to drink early and often is bad. There’s also no need to over hydrate the day before and the morning of a race. Drink to thirst. I know I already said that.

– Take salt to increase the sodium content. Salt is the key to prevent EAH. Endurolytes, S Caps, etc, have other electrolytes as well, and those may be needed for other factors. This talk really was limited to EAH. Gels don’t have enough sodium to help much for this, though I just checked my Gu packages and Roctane has 3x the sodium of normal Gu. I always wondered why that was marketed to ultra runners, now I see why. On a hot day, you’ll need to drink more to replace fluids sweated out, so you’ll need more salt. To my recollection he talked in terms of a fast food style packet or two of salt per hour. When I look at my Endurolytes bottle, it says 1-3 per hour. Ultra aid stations should always have salty foods available, so take advantage of them.

– NSAIDS (Advil/ibuprofen and Aleve/naproxene) reduce the kidneys ability to process blood and often result in decreased sodium content. He said a number of times not to take them before or during, at all. I asked about taking a minimal amount, and he agreed that it reduced the risk, but also probably wouldn’t be enough to help with the pain. I also asked about acetaminophen/Tylenol, and he said that didn’t cause issues related to EAH. However, this talk ONLY covered EAH and I believe Tylenol can affect your liver, so do your own research and be careful with this.

– Sometimes you will stop processing water and it will slosh around in your stomach. Beware of this because when you stop or your system otherwise recovers and you start processing the water, it will further dilute the sodium content. I think this is why sometimes people have serious problems with EAH following the race. It follows that you should continue taking salts as you rehydrate after the race.

– People asked about dehydration, and he pretty much indicated that hydration isn’t as serious of a problem and it is easily corrected by taking more fluids. I want to be careful here and not underplay dehydration. Again, 400-800ml/hour is not a small amount, so don’t think you should barely be drinking.

– Losing salts through sweat is a factor as well, though Dr. Rosner said the salt concentration in sweat isn’t as high as you’d think. Simply replace the fluids lost through sweating, but take more salts if you’re taking more fluid.

So to summarize prevention in endurance events (over 4 hours), supplement your salts, don’t over hydrate, and don’t take NSAIDS such as Advil or Aleve.

Detection is very tricky, because many of the signs of EAH present similar to those of dehydration and/or heat exhaustion. The only real indicator is a device to actual measure sodium levels in the blood, and such a portable analyzer costs $5K. He thinks every endurance race should have this device. I have no idea which ones do.

– Symptoms such as cramps, salty face, swollen fingers, confusion, dizziness and urine color aren’t reliable signs of hyponatremia. However brown/red urine is bad, but that can be hard to tell from dark urine indicating dehydration.

– Weight (weighing more after an event) is a decent indicator of a problem, but still not that reliable. Unless you really eat a lot, you should weigh the same or 1-3% less. If you’re >4% over start weight, you’re probably at higher risk because this indicates you’ve taken too much fluid. One study showed this well, but in another it didn’t correlate too well at all. One of the studies, I forget which one, was from Western States runners.

After all this, the incidence of serious problems with EAH is still pretty low. Unfortunately there is no set formula to say exactly how much to take as everyone is different. Ideally you could measure your inputs and take your sodium levels before and after and event and adjust accordingly, but most of us probably won’t have that chance. He said to learn what your body needs and what has worked for you and what hasn’t.

Treatment is to get more salts back into your body, either orally or with an IV of 3% saline solution. Recovery can be rapid. The difficulty is that if the problem is identified as dehydration and the typical lower saline IV solution is given, it dilutes the sodium even more and makes the problem worse. Of course if you are out of it you probably won’t be questioning what the medical staff is doing to you, thus I’ve focused on prevention here. However, if you’re assisting a friend at the finish or pacing or crewing during a race or working an aid station, be aware to push salts and not just fluids and also be aware of the runner’s mental condition.

Anyone who was there or is knowledgeable about this, please correct anything I got wrong or omitted. This is an important topic and the information needs to be accurate.

Bob Clouston


2 thoughts on “Summary: CAT Talk on Exercise Associated Hyponatremia

  1. chrisamymc

    Really nice job, Bob. As an endocrinologist with a personal and professional interest in EAH, I’ll briefly reiterate. The most important key to avoiding EAH: do not overdrink. Hyponatremia is primarily an excess fluid problem; it is much less a problem of reduced sodium content. Drink if you feel thirsty. If you are ambivalent about fluid (i.e., about whether or not you’re thirsty), do not feel compelled to drink. The commonly-floated notion that you must drink before you get thirsty (“if you wait until your thirsty, it’s too late”) is not good advice; this approach does not improve performance (compared to drinking to thirst) and it can increased the likelihood of EAH. Liberalizing sodium intake can also help. And avoid NSAIDs like ibuprofen — these drugs are likely a risk for EAH (and also renal failure).

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