From Fellrnr.com, Running tips
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As an aside, if you have low blood pressure, which I do, increasing your salt intake can really help.
= Caffeine and Alcohol =
The scientific evidence shows that
caffeine is generally not a diuretic<ref name="ref5"/><ref name="ref14"/><ref name="ref15"/>. Previous studies have shown that if you don't normally take caffeine and then get a large dose, there is some diuretic effect. However normal intakes of caffeine by non-users and use by regular users is not a diuretic<ref name="ref16"/>. (If you urinate more because you drink a 20oz Latte, it is because of the 20oz of fluid, not the caffeine.)
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"/>.
= Cramps =