I jumped on the caffeine train and have yet to get off. I didn't do any research before I got on however, I didn't know anything about what it might do to my blood sugar or how it would affect my body. That is the sign of a true drug, we don't know what it will do, we just want it because it helps us. Over the past couple of months I have talked to a few doctors to see if my pre race caffeine fix was safe. What I have learned is that it is ok, each doctor has said "make sure you hydrate with caffeine" I had never thought about caffeine and dehydration but it does make sense, if I'm drinking a cup of coffee I'm probably not going to drink a 16oz water. I was just drinking coffee and that filled me up, as the day goes on I'm missing probably 32 to 48 ounces of water because I replaced my water for two hours with coffee.
As far as blood sugar and caffeine I have been told that I have nothing to worry about that a cup of coffee will do no harm to my body in anyway. I did find a nice article from Diabetes Mine entitled The Great Coffee Experiment which is a good read. I will continue to use caffeine before races and will do so without worry, it helps me as an athlete and has no effect on my blood sugar. Knowing that I can't go wrong with a nice little pre race caffeine jolt before I jump on the bike or run mile after mile is good to know.