Promiscuity Improves Female Fertility, Study

Sex is good for fertility, two new studies reported.

According to researchers from Indiana University, women who regularly have sex ended up developing different immune systems in comparison to women who did not have sex all the time. The researchers believe that this difference is what increases women's fertility even if they are outside of the "ovulation window."

Specifically, the research team found that the immune systems of more sexually active women tended to release more "Type 2 helper T cells" and immunoglobulins/antibodies in two separate studies that examined the same data set. The team concluded that the systems of sexually active women reacted this way in order to prepare for the possibility of a pregnancy.

"This research is the first to show that the sexual activity may cause the body to promote types of immunity that support conception," Tierney Lorenz, the lead author of the report and a visiting research scientist at the Kinsey Institute in Sex, Gender and Reproduction at Indiana University, said in the press release. "It's a new answer to an old riddle: how does sex that doesn't happen during the fertile period still improve fertility?"

Lorenz explained, "The female body needs to navigate a tricky dilemma. In order to protect itself, the body needs to defend against foreign invaders. But if it applies that logic to sperm or a foetus, pregnancy can't occur. The shifts in immunity that women experience may be an answer to this problem."

For this research, the team had examined healthy female participants from Kinsey Institute's WISH (Women, Immunity and Sexual Health) Study. Data included the women's menstrual cycles and sexual activity levels. The researchers collected saliva samples for both of the studies.

"We're actually seeing the immune system responding to a social behavior: sexual activity," Lorenz said.

The studies were published in the journals Fertility and Sterility and Physiology and Behavior.