One frustratingly stubborn stereotype about women is that their brains work at less than peak performance during their menstrual periods.
Well, a new study may finally put that old canard to rest. In what appears to be the largest study on the topic to date — and the only one that followed women over more than one menstrual cycle — European researchers found that hormonal fluctuations during the menstrual cycle do not have any effect on women’s ability to think clearly.
“The hormonal changes related to the menstrual cycle do not show any association with cognitive performance,” said Brigitte Leeners, the study’s lead author and a reproductive endocrinologist at University Hospital Zurich, in a released statement. “Although there might be individual exceptions, women’s cognitive performance is in general not disturbed by hormonal changes occurring with the menstrual cycle.”
As Leeners and her colleagues point out, previous studies that have suggested women become more cognitively muddled at certain points during the menstrual cycle have had all sorts of design flaws. Most notably, they involved less than 30 women (sometimes less than 10) and observed the women over a single menstrual cycle.
Those methodological biases can easily lead to “spurious false-positive” results, the researchers point out.
The current study tries to address those problems. It included 68 menstruating women, aged 18 to 40, and followed them through two menstrual cycles. At four different times during each cycle, the participants had blood samples taken to measure the levels of various hormones — particularly estrogen, progesterone and testosterone — circulating in their bodies. Those hormones are known to fluctuate throughout the menstrual month.
The women also underwent neuropsychological tests that measured changes in three cognitive functions: attention, working memory and cognitive bias (errors in thinking that can affect decisions and judgment).
An analysis of all the collected data found that while some hormones in some women were associated with cognitive changes across one menstrual cycle, those effects did not repeat in the following cycle.
Overall, none of the hormones studied had any replicable, consistent effect on the women’s thinking skills.
Limitations and implications
This study, of course, has its own limitations. Although it included more participants than previous studies, 68 is still a relatively small number. Leeners and her colleagues say studies with larger numbers of women, including subsets of women with hormone disorders, are needed to verify their results.
They also emphasize that all future research on this topic must include data from a second menstrual cycle.
Until studies with improved methodologies are done, they warn, any positive findings in the published scientific literature about the menstrual cycle having a negative effect on cognition “must be interpreted with reservation.”
After all, their study’s failure to replicate such an association demonstrates “how easily irreproducible false-positive findings can emerge in neuroendocrinological research.”
And also how persistent gender stereotypes can be.