SpeedyGeoff is an Australian-based blog about running. In the post below he discusses that while there is some help coffee can give to runners, there are a number of benefits to giving up. He also plays his system by giving up and then having a coffee just before a race, to get extra benefits.
It is a bit tough giving up coffee when you run long distances. But for me, the tiredness only lasts a couple of days. Here is my experience of what happens, I have given up a few times. The first thing is, I catch up on lost sleep! Next I have minor cold symptoms, which are actually my sinuses coming good. And soon, as the energy returns, I discover that I can run quickly at the start of races, because my energy reserves are not being compromised by the effect coffee has when it releases fats in preference to glycogen at the start of exercise. Lastly, I should find that when before a marathon or similar endurance race I do allow myself one rare cup of coffee, drinking it for its fat-releasing and therefore energy-conserving effect will be enhanced simply as a result of my not being accustomed to it.