I would think that a calorie amount that is safe when you're not on your period is safe when you are. I did read recently that women tend to eat more when they are on, but not that more calories are needed, not like breastfeeding, for example.
"If you drop an egg, you don't say, 'Oh, shoot' and drop the other 11, do you?"
-Source unknown, but obviously brilliant
Reached goal 4/16/2010...but kind of afraid to look these days