This was the first I had heard of it and it blew my mind. How the hell does just hanging around someone make your periods sync up? I'm sure there is some scientific reason for it, but I would rather not google that at work.
Is it common knowledge that girls can sync up? An interesting study would be if girls that live together are more often in sync than chance would allow. I have no idea what porpoise this study would serve, but I wonder that about lots of studys I read about, so I'm sure someone has the money to fund it.
My office is about 90% women and I'm pretty sure we've all synced up. And I'm pretty sure the few guys (all managers) we have in the office have caught on to this as the last few months they've managed to bring in chocolate treats and be more supportive at just the right time of month.
Not only do girls sync up, but guys also have monthly hormonal cycles that sync up with each other and with women. No physical pain or the obvious thing, but just a general mild exhaustion and moodiness occurs in men.