I overheard some guys talking about this at the gym. I'm not sure if it's true or not so I am asking here. He said that he usually donates blood 3/4 into his cycle because it helps reduce the level of something (don't remember the word he used) in his blood.
So is it a good idea to donate blood during the end of a cycle or is all this just BS. If it is true, but does it help lower?