New research provides evidence that natural fluctuations in women’s hormones are not only associated with their own psychology, but also their partner’s perception and well-being.

The study, published in Biological Psychology, was the first to examine how the rise and fall of women’s hormones during the menstrual cycle impacts their partners’ feelings and perceptions.

“Hormones have an underappreciated effect on behavior. This is true for men and women, just as it’s true for animals of other species,” said study author Francesca Righetti, an associate professor at VU Amsterdam.

“Researchers have begun to explore how the hormonal variations that naturally and reliably occur across the ovulatory cycle – specifically, variation in the hormones estradiol and progesterone – affect how women think and feel.”

“But less work has examined how variation in hormones affect both members of a relationship. Given our interests in romantic relationships, we aimed to better understand what aspects of romantic relationships vary as a function of these hormones, and which do not.”

The researchers collected urine samples from 33 women for 15 days to measure changes in estradiol, progesterone, and testosterone levels. During these 15 days, the women and their male partner also completed nightly surveys regarding their relationship satisfaction, perceptions of their partner, and other factors.

All of the relationships had lasted for more than 4 months and none of the women were using hormonal contraception.

Righetti and her colleagues found that both women and their partners evaluated their relationships more negatively on days in which women had higher estradiol levels. As estradiol increased, women also evaluated their partner as less physically attractive.

“Women’s hormone levels change across their ovulatory cycles, and these changes are likely to affect their psychology and, perhaps, the way they feel toward their romantic partner. We found that the hormone that peaks just prior to ovulation, estradiol, was associated with more negative partner evaluation,” Righetti told PsyPost.

Women’s estradiol levels were also associated with their partners’ self-reported well-being. “Men also perceived their partner to be less satisfied when estradiol was high and, consequently, they experienced lower well-being,” Righetti said.

Despite the changes in sexual attraction, however, hormonal fluctuations were not associated with having sexual intercourse .

“We’d like to emphasize that our study investigated changes within couples. Some relationships are especially good, and some relationships are especially bad,” Righetti said.

“Changes in naturally varying hormones aren’t going to turn a bad relationship into a good one, or a good relationship into a bad one. But they might influence some subtle changes within a relationship – like adding some minor turbulence to what is a great relationship on the whole, or temporarily making things a little nicer for a relationship that is pretty rocky.”

The study — like all research — includes some limitations.

“Given the difficulties in recruiting couples under 40 not not using hormonal contraception, our sample size is rather small, and replication is needed to ensure the robustness of the findings,” Righetti explained.

It is also unclear why higher levels of estradiol were associated with reduced relationship satisfaction among women.

“Evolutionary theories have suggested that, when women are ovulating, they may be especially tuned into other men (e.g., men with good genetic qualities), and that’s why they distance themselves from their primary long-term partner. Our data weren’t totally consistent with this perspective, though, since estradiol was not associated with the degree to which women reported flirting and giving more attention to other men,” Righetti said.

“But this may be due to the fact that, given our small sample, our female participants may not have encountered many attractive men during the duration of the studies. On the contrary, it may be that evolution has shaped women to pre-emptively disengage from their partner close to ovulation to be open and attentive to identify alternative partners that may be especially good reproductive partners.”

The study, “How reproductive hormonal changes affect relationship dynamics for women and men: A 15-day diary study“, was authored by Francesca Righetti, Josh Tybur, Paul Van Lange, Lea Echelmeyer, Stefanievan Esveld, Janique Kroese, Joycevan Brecht, and Steven Gangestad.