Safe Hydration for Ultra Marathon and Endurance Running

Safe Hydration for Ultra Marathon and Endurance Running

Safe Hydration for Ultra Marathon and Endurance Running

Staying Hydrated – The Safe Way

Author: Dr. Aaron Reilly, DO | Medical Director


When it comes to endurance events, having a hydration plan is one of the most important strategies to solidify. Most racers are aware that not maintaining adequate fluid intake during the race can lead to dehydration, and dehydration is bad. What a lot of racers aren’t aware of is that there are complications of over consuming fluids as well, which range from uncomfortable to potentially fatal.


Most runners have experienced “slosh stomach” – the feeling of a full stomach, nausea, bloating, and sometimes vomiting that occurs while drinking fluids during a run. A more serious complication of over-hydration is known as “water intoxication”, or exercise associated hyponatremia. This is caused by dilution of the sodium in the blood due to free water retention.


In regards to hydration, maintaining the zone between dehydration and over-hydration can be difficult. Several strategies to prevent dehydration include monitoring frequency of urination, urine color, and drinking on a set schedule. The problem with all of these techniques is that they really aren’t reliable and can lead to over-hydration. This is because prolonged exertion causes changes in the way that the body normally handles fluid management and urine concentration. It does this by increasing a specific hormone, anti-diuretic hormone (ADH), which triggers the kidneys to retain water. This decreases urination, and makes the urine darker and more concentrated. Therefore, it is possible to have highly concentrated urine and decreased urination and actually be over-hydrated.


While it is common to attempt to prevent water intoxication by consuming electrolyte tablets, there is no data to show that this method is effective. In fact, there is some evidence to shows that high doses of sodium supplementation actually increases thirst, which in turn increases the amount of fluid intake. Since prolonged exertion, among other factors, triggers ADH, the kidneys retain more free water, and may actually increase the risk of hyponatremia. Electrolyte tables can also decrease gastric motility, which means that more fluid will remain in the stomach and may lead to slosh stomach.


So what is the best approach? The answer is it depends. There are many factors that affect sodium loss and fluid retention. My advice is to stay consistent. If you choose to use electrolyte supplements, make sure to train with them. Also, make sure to use the same brand and the same amount during the race that you train with, as different brands will vary drastically on the contents of the supplement. Drinking to thirst is the first step – if you are thirsty, drink up. In addition, pay attention to your urine, but not in the traditional sense. If you are drinking to thirst, but have very dark urine or decreased urine, a trial of modestly increasing fluid intake is reasonable. If this does not lead to increased urination, then the issue is probably less related to dehydration and more related to ADH. A good strategy in this case is to take a 10-20 minute rest (or until you are able to urinate). Pausing from exertion will often lead to decreased ADH and increased urination.


In summary, it can be difficult to maintain the balance between dehydration and over-hydration. The keys are training how you plan to race, drinking to thirst with minimal deviations, and taking urination breaks will often let you know how your body is doing. Pay attention to your hydration and try to keep things consistent, and you will be able to maintain a suitable equilibrium.

About the Author

Leave a Reply