By Justin Lehmiller

Women naturally experience a number of hormonal fluctuations over the course of the menstrual cycle, and we’ve long known that these fluctuations are linked to changes in women’s psychology and behavior.

However, very little research has explored the implications of these hormonal shfits in long-term relationships. So what is the impact of the rise and fall of specific hormones, and how does it affect both partners in a couple?

A new study published in the journal Biological Psychology is the first to address this and the results are fascinating [1].

Thirty-three heterosexual couples in the Netherlands participated in this research. Couples had been together, on average, for about four years. Participants were age 26 on average and none of the women were using hormonal contraceptives.

Each day for 15 days, women and their male partners completed a survey that included questions regarding how they felt about their partner, how the think their partner feels about the relationship, the degree to which they felt jealous, their level of interest in sex, and their psychological well-being. In addition, all participants collected a daily urine sample, which was used to look at hormone levels.

For the women, researchers assessed changes in estradiol, progesterone, and testosterone; for men, they only looked at testosterone. Men’s testosterone levels were assessed here in order to determine whether they were potentially responsive to fluctuations in their partner’s cycle. 

The key findings were as follows: on days women experienced increases in estradiol (a hormone that reaches its peak right around the time of ovulation), they tended to evaluate their partners more negatively. In addition, high estradiol was linked to both men and women perceiving that their partner felt more negatively about the relationship.

The researchers also found that on days estradiol was elevated, women reported less physical attraction to their partners, while men reported lower levels of sexual desire and perceived their partners as less interested in sex.

Men also reported lower psychological well-being on days their partners had higher levels of estradiol and subsequent analyses showed that changes in the way women evaluated their partners accounted for this effect. In other words, this pattern of results suggests that men’s lower well-being stemmed from them picking up on their partner’s negative evaluations.

These effects only emerged for women’s estradiol levels—no such effects were found for changes in women’s progesterone or testosterone levels.

However, the researchers did find that elevated progesterone (which rises following ovulation as estradiol drops off) was linked to more positive evaluations of their partner and better psychological well-being. 

Lastly, they found that changes in women’s testosterone were linked to corresponding changes in men’s levels of this hormone—in other words, as women’s testosterone went up, so did men’s. Further, on days testosterone was higher, both men and women reported greater levels of jealously.

Interestingly, no hormonal changes were linked to changes in sexual frequency. Thus, while hormonal fluctuations were linked to various psychological differences, they weren’t related to changes in actual sexual behavior. 

Of course, it’s important to put all of these findings in context. The results come from a relatively small study of young adults who were only tracked over a two-week period. It’s therefore important for these findings to be replicated in a larger and more diverse sample before drawing firm conclusions. It would also be important to explore these effects over a more extended period of time in order to determine whether there are any long-term implications.

In addition, future research is needed to understand why these hormonal changes predicted the outcomes that they did. For example, why are increases in estradiol linked to women viewing their partners more negatively?

Evolutionary theorists have argued that it may be because when women are most fertile (and when estradiol levels reach their peak), they become more interested in “manly” men with greater genetic fitness (i.e., genes that promote health and attractiveness)—and, indeed, some research has found support for this idea [2]. Put another way, when women are most likely to conceive, they are thought to become attuned to partners who would offer the most genetic benefits to their children.

Putting all of this research together, one interpretation is therefore that women are perhaps disengaging with their long-term partners to some degree when they are most fertile in order to make themselves available for other reproductive opportunities that might come along.

Although we must await the results of future research to learn more, these findings suggest that the hormonal changes women experience during the menstrual cycle appear to affect the way that both women and men feel about their relationships.

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Dr. Justin Lehmiller is an award winning educator and a prolific researcher and scholar. In addition to publishing articles in some of the leading journals on sex and relationships, he has written two textbooks and produces the popular blog Sex & Psychology. Dr. Lehmiller’s research addresses topics including casual sex, sexual fantasy, sexual health, and friends with benefits. His latest book is Tell Me What You Want: The Science of Sexual Desire and How It Can Help You Improve Your Sex Life. Follow him on Twitter @JustinLehmiller or facebook.com/psychologyofsex.