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== More on Hyponatremia ==
Hyponatremia is where the sodium (salt) levels becomes too dilute. Initial symptoms tend to be a gain in weight and a general swelling and 'puffiness', most noticeable in the hands. More severe symptoms are caused by a swelling of the brain (cerebral edema) including nausea, vomiting, headache and malaise <ref name="ref10"/>.
The cause of Hyponatremia is poorly understood, but believed to be related to excessive water intake <ref name="ref1"/>. (I believe that this is excessive fluid intake in the absence of sufficient electrolytes.) Hyponatremia can be common in endurance athletes. In a 1997 Ironman triathlon, almost 4% of competitors received attention for Hyponatremia <ref name="ref4"/>. In a study of the 2002 Boston Marathon, 13% of finishers had some level of Hyponatremia, and 0.6% had critical Hyponatremia <ref name="ref2"/>. The study revealed that the risk factors for Hyponatremia include a slow finish time (>4 hour) and consumption of >6 pints (3 liters) of water during the race; BAA suggests a 'slight build' is also a risk factor<ref name="ref12"/>. Healthy 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 >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.
== HypERnatremia - the opposite of HypOnatremia ==
<ref name="SYMPT">Sensitivity and specificity of clinical signs for assessment of dehydration in endurance athletes
<ref name="ref14">Metabolic and exercise endurance effects of coffee and caffeine ingestion