Women getting their periods in synch?

I have heard that women who live together get their periods at the same time; some female friends of mine confirmed that this was true, at least in their case.

But if this is true, do women in large groups get their periods at the same time – all the women in an office building for example? After all, they may be working together in close quarters for over 40 hours a week, and may well be spending as much time in the office as they do at home among those they live with. Is this possible? And if it is possible, what about an even larger population set – say, all the women in a city with a high population density?

I worked in a vet clinic where the only two males on staff were the two vets, and we were all pretty close together. It could really make for some bitchy days until about 5 of us got on depo! There were 6 up front, counting the office manager, and 6-7 in back. Of course we weren’t all there at the same time every day, but it still seemed to work out that way.

Despite the Straight Dope Classic, I have read that the studies suggesting a synchronisation of menstruation use faulty analysis of data and there is in fact no such synchronisation.
Now, to find the cite.

Here it is. I’ll see my cited Straight Dope Classic 1986 and raise me a Straight Dope Classic 2002.

Regardless of what Our Great One has stated, IME it’s quite true. I’ve lived in a couple of half-way houses/rehabs and worked in many an office with other women. I’ve found it almost certain that at least one or two (work situation) would be in sync with me. In the rehab, there would be 15 of us at the same time. A phenomenon, I tell you!

My daughter and I are in sync. She starts first, then I’m a couple of days later. She just started her period last Halloween, so I don’t know if it’s genetics (I’m regular, myself) or if we’re in sync.

FWIW, I’m at work during the day while she’s in school or at home, so the only time we have together is evenings and weekends.

Just out of curiousity, how do you know? My department has five women, and I know I’ve never announced, “I have my period! Who’s with me?” at the weekly meetings. :confused:

The thing is, there’s only four weeks each month to have your period. Odds are good that someone in your office is “synched” with you even if you’ve never met her, especially if you’re in a big office. More especially, if you consider a few days away to be “synched”.

That said, I have watched my period move around the calender when I’m in prolonged and close proximity with one particular friend. Our other girlfriends’ also move to match her cycles. It’s like she’s the alpha bleeder or something. We’re FAMers, so we do discuss things like periods and cervical fluids and, more importantly, we have our cycles down in writing and can verify the changes that occur. This was when we were working together at a close-quarters sweaty job (harvesting plants and making medicines) or when we’re camping close to each other for an extended period of time, but when we were doing normal office work in the same building but not close to each other, my cycle would drift away from hers again.

Since we’ve become less physically close (we don’t work together anymore), my cycle is very regular and doesn’t move around a bit, just like it was before we worked together.

So what is the cause and/or purpose of this phenomenon?

Might be just a side effect of hormonal link people tend to have with each other through pheromones (not very confirmed scientifically). I’ve lived with three women, and let me tell you, not only were they in sync, the girl who started first was always the same and if she was late a little the rest of them were too - I called her alpha. In fact, when the three of them would just start there were incidents where it would prompt a friend who stopped by for just a few hours to start, sometimes up to a 10 days earlier than expected.

No cite (sorry), but I remember reading about an experiment like this. Basically pheromones were applied to the upper lip of the participants and their periods did sync up.