Caffeine: Diuretic?
For those who drink caffinated drinks and use caffeine tablets during the marathon:http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0084154
The primary finding is that if you are a caffeine user, your urine production is not higher and drinking coffee, as an example, can actually still count as part of your hydration strategy. Of course, this means using moderation.