The nail on the toe next to my big toe (on both feet) gets sore, black, and kinda loose whenever I do a long training run or a race. So far, I've been very lucky because I've never lost a toenail completely like many runners do. And I want to keep it that way! I don't want to think about what my endo would say if I showed up for my next appointment missing a toenail! I wish there was some information out there about anything I should do differently if I lose a toenail since I have diabetes. I know I'm supposed to take really good care of my feet, but running is not something I'm willing to give up, or even cut back on.
From what I've read and heard, the cause of black toenails is usually shoes that are too small or too big. My running shoes are already a size larger than my regular shoes, but I might have to try going up another 1/2 size and see if that makes a difference, because I know my shoes are not too big. I think it's time for a new pair of running shoes anyway, and I got enough money for my birthday to get a pair. Hopefully I'll even have enough money to get a few new pair of socks too!