My boyfriend lived with me, in my room for over half a year and my cycle never changed. My cycle has changed slightly due to birth control though.

ive never heard that but it has been shown that women who live closely affect each other's cycle, so their periods become synchronised. this is thought to be an evolutionary device to make sure all the females in one area are ready to conceive at about the same time. its also true of animals. but like i say, i havent ever seen any research about men altering females' menstrual cycles

Yes, but how it's affected does depend on who the male is. There's one study by Singh et al that researches the age of menarche in girls with two parent families, one parent families, and single mother families. Females that live with their biological father have their first period later than females that live with a stepfather or no father, even those raised by the stepfather as if he was biological. I'd really like to see this study expanded to include single father families, two father families, and more girls of adoptive parents. The results were significant, but need to be reproduced. As to other men affecting a grown woman's cycle, yes. A single woman's cycle often speeds up or slows down due to surrounding factors. A woman may ovulate sooner than she expected to because she met a guy she likes and spends time with alot. Or she may ovulate a few days late because she's been cooped up and won't go out until the weekend. It's hard to reproduce these individual cases in large studies though, since it's difficult to craft a study that would yield usable results. As to women menstruating at the same time, there's more anectdotal evidence than there are good conclusive studies. Many studies say yes, some say no effect, a few even said women's cycles differentiate when they spend alot of time together. To get more info, we need in depth and longitudinal studies. We need to see if cycles are more likely to synch up in relatives than friends. We need to see if they change when one roommate gets a boyfriend or a male roommate moves in. It may turn out that menstrual cycles adapt to not just other cycles, but to individual mating situations.

It's usually not men who affect a woman's cycle, it's other women. Often all the women in a home or a close group of friends that spend a lot of time together will all cycle together. It takes some time but I've had it happen to me often. It's interesting how our hormones can affect other people that way. I know several friends didn't appreciate it when I was having very short period cycles and they started having them much earlier as well. I wish it had been the other way around and their cycle length had made mine further apart LOL!!!