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Myth: Caffeine is dehydrating and should be avoided, especially before exercise

TRUTH:  Caffeine is one of the most popularly used and socially accepted stimulants across cultures – yet Americans have the idea that it causes dehydration engrained in our brains!  The theory is that since it’s a diuretic, caffeine increases urination so it is dehydrating.  But, this like so many things, readers, is false.  Research shows that it doesn’t significantly increase the frequency or volume of urination and more than drinking water.

So that leads me to the other half of this myth: should caffeine be avoided during exercise?  Not necessarily.  While caffeine is a mild diuretic, it is still a stimulant.  In some people, the added stimulation improves the ability to concentrate, improves alertness, and improves response time.  Also, stimulants (like caffeine) may be particurarly beneficial to endurance athletes since they promote fat metabolism.  On the other hand, stimulants can cause fast breathing, increased blood pressure, nervousness or an upset stomach.  Or, they can cause insomnia (and if sleep is lost, performance will certainly be diminished). 

BOTTOM LINE:  All people, including athletes, respond to caffeine differently.  The only way to know whether it will help or hurt an individual’s athletic performance is to test it during practice or training.  Recent evidence suggests that consuming a moderate amount of caffeine per day (up to 300 mg) may have cardiovascular benefits.

  • One grande (16oz) coffee at Starbucks has about 330mg of caffeine.
  • One medium (16oz) coffee at Dunkin Donuts has about 143 mg of caffeine.
  • One medium (16oz) green tea has about 160 mg of caffeine.


  1. New York Times:
  2. Mayo Clinic:

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