I don't know the math, but high amounts of caffeine is a diuretic, beer too, and can cause dehydration. I have heard for every cup of coffee, drink a glass of water to replace the loss. Green tea is higher in caffeine than other types teas, but may have more added health benfits. Coffee also, and I made a poat in "adjuntive treamant" in reagrds to recent study saying that drinkig coffee reduced oral cancer risk by 50%, which was not seen in tea or decaffenated coffee.

http://www.livestrong.com/article/294664-diuretic-effects-of-caffeine/

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