From Fellrnr.com, Running tips
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== Introduction ==
The advice given to runners on hydration has changed over time and looks set to continue to change. There are competing forces at work - sports drink manufacturers, event organizers (often sponsored by the manufacturers) and scientists (some also sponsored by the manufacturers). One thing is clear about hydration - it is important. Incorrect hydration can lead to impaired performance, and in extreme cases, death.
== Effects of dehydration ==
There is a table showing a range of values at [[Sodium Loss]].
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"/>.
Alcohol is another story; drinking anything stronger than 2% will cause dehydration. Because alcohol takes 36 hours to clear the body, it should be avoided for 48 hours before you wish to avoid impaired performance<ref name="ref5"/>.
Muscle Cramps ==The common wisdom that muscle cramps are caused by lack of electrolytes or dehydration does not appear to be supported by science <ref name="ref6"/>.
== Blisters and black toe nails ==