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The cause of Hyponatremia is poorly understood, but commonly believed there appear to be related to excessive two likely causes in runners. # Excessive water intake can cause 'dilutional Hyponatremia'<ref name="ref1"/>. HoweverHealthy kidneys can excrete about 2 pints (1 liter) of fluid per hour, but this may be reduced by exertion or illness <ref name="ref3"/>. So drinking &gt;6 pints in 4 hours could easily exceed the kidneys capacity to cope. The recent rise in Hyponatremia may be due to earlier advice to athletes to "drink as much as possible" <ref name="ref13"/>, combined with a general concern about salt intake.# For ultrarunners, I would argue that Hyponatremia is more likely to be caused excessive fluid intake in the absence of sufficient by a insufficient electrolytescombined with appropriate drinking. ==Likelyhood==Hyponatremia can be common in endurance athletes:

The study <ref name="ref12"/> revealed that the risk factors for Hyponatremia in marathons include

* BAA suggests a 'slight build' is also a risk factor<ref name="ref12"/>=Preventing Hyponatremia==The key to preventing Hyponatremia is to ensure adequate electrolyte intake and to drink when thirsty. See [[Practical Hydration]].