Infertility Linked to Women's Immune System: A Study

Infertility in women may be tied to the immune system based on a new study published in the American Journal of Human Biology.

Because an animal’s energy has to be carefully allocated, according to Kathryn Clancy, the lead author and professor of anthropology at the University of Illinois, its first priority are those tasks necessary for survival, including immune function, with leftover energy dedicated to reproduction.

The study included a group of healthy, premenopausal women who participated in traditional farming practices.

The researchers then collected the women’s saliva and urine over one menstrual cycle during harvest season when physical labor levels are at their highest and thus when physical work calls upon more of the available energetic resources.

Specifically, the researchers tested ovarian hormone levels and levels of C-reactive protein (CRP), a commonly used marker of inflammation.

“Depending on other factors that you look at alongside it, CRP can tell you about immune function or it can tell you about psychosocial stress, because CRP has been correlated to both of those things in other populations,” Clancy said.

Sure enough, the researchers found that in women with high CRP, progesterone was low. Furthermore, they discovered that the sex hormone estradiol and the age of first menstruation were the strongest predictors of CRP levels.

While it’s too early to tell whether these relationships are causal or not, Clancy believes it boils down to two possible explanations.

“One is that there is an internal mechanism, and this local inflammation drives higher levels of CRP, and that is what’s correlating with the lower progesterone,” she said. “The other possibility is that there is an external stressor like psychosocial or immune stress driving allocation to maintenance effort, which in turn is suppressing ovarian hormones.”

Knowing this, Clancy said, not only could help women better understand their bodies, but explain the timing of different life events, such as the timing of puberty or children. 

“It’s really interesting to see the interplay between a person’s intentions about when and why to have children, and then their own body’s allocations to reproduction or not,” she said.