Not that you really need it, but here’s another reason to have sex: It’s great for your immune system. According to new research, frequent coitus triggers the body’s natural defenses in positive ways and may jumpstart physiological changes that boost a woman’s chance for conceiving.
The results of the study were published Tuesday in two papers, one in the journal Fertility and Sterility and another in the journal Physiology and Behavior. The papers suggest that having sex during points of infertility in a woman’s cycle could still help improve her chance of conceiving.
For years, physicians have known that sex outside of a woman’s fertile period could increase her chances for getting pregnant, but they weren’t sure why. The study sought to make sense of this biological conundrum. "It's a new answer to an old riddle: How does sex that doesn't happen during the fertile window still improve fertility?" Tierney Lorenz, a visiting research scientist at the Kinsey Institute and lead researcher on the study, said in a press statement.
For the study, researchers at the Kinsey Institute and Indiana University analyzed data from the Kinsey Institute’s Women, Immunity and Sexual Health study, a sample of 30 healthy women; around half were sexually active, and the other half were not.
In the paper published in Fertility and Sterility, researchers found that sexually active women had higher Type 2 T-cell counts during the luteal phase of the cycle—when the uterine lining thickens after ovulation and before a period starts, when a woman is most fertile. Type 2 T-cells help create a more hospitable environment for conception; without functioning Type 2 T-cells, the body’s the immune system would otherwise attack sperm cells and an emerging embryo.
The researchers also found that during the follicular phase of the menstrual cycle—the period of time before ovulation—Type 1 T-cell count surged in sexually active. This helps the body safeguard against illnesses and infections that could ultimately inhibit a woman’s chance of becoming pregnant.
The second paper looked at immunoglobulin antibody levels in women who were sexually active and compared them to the levels in those who were not. These antibodies are produced by white blood cells and are critical to fighting off bacteria, viruses and other microbes. The researchers found that sexually active women had higher levels of certain antibodies at different times of their cycle, and the pattern reflected the body’s efforts to ramp up its protective defense to prepare for the potential for pregnancy. The researchers did not observe the same fluctuations in T-cell counts and immunoglobulins in non–sexually active women.
The research could influence what recommendations physicians make to couples about how often to have sex if they’re trying to conceive. Currently, many physicians tell couples that more sex is better, but to be sure they spend extra time in bed at the peak in a woman’s cycle when she is fertile (the five days leading up to ovulation). But the study suggests sex at other points throughout the cycle may also play a role in fertility, and that means physicians might tell couples who want a baby to have more sex throughout the entire month.