Menstrual cycles alone do not have a direct effect on mood in healthy young women with regular cycles, finds a new University of California, Irvine (UCI)-led study that points to sleep as the culprit instead. 

Poor sleep, researchers discovered, is to blame for negatively shifting emotional states directly before and during periods. Findings, published in SLEEP, may seem surprising, says lead author Alessandra Shuster, UCI cognitive sciences graduate student and researcher in the Sleep and Cognition Lab, because they fly in the face of a long-held stereotype.

“There is a general belief that women are highly affected by their menstrual cycle, specifically that women get more irritable and emotionally unstable during their period,” says Shuster in a release. “But there hasn’t been a lot of research to back up that belief for the majority of women in the US who do not report clinical premenstrual or mood disorders, and findings have been inconsistent at best.”

Previous work has shown that sleep can impact mood, so researchers from the Sleep and Cognition Lab at UCI and the Center for Health Sciences at SRI International set out to measure if a good night’s sleep might be a protective factor in the relation between mood and menstrual cycle.

They enlisted the help of 72 healthy young women, ages 18 to 33 with consistent sleep schedules, regular 28-day menstrual cycles, and no pre-existing menstrual-associated, major medical or psychological disorders. For two months, participants kept an online daily diary in which they self-reported details each morning about their previous night’s sleep including sleep quality, duration, number of times they woke in the night, and how long it took them to fall asleep. Each evening, they assessed their overall positive and negative mood for that day. They also marked whether they had started or were on their period. During the second month, participants wore an OURA ring which tracked objective sleep measures. 

Researchers paid particular attention to the relationship of variances in mood and sleep before, during, and after participants’ periods.

Using statistical analysis, they discovered that menstrual phase alone did not predict mood, but a poor night of sleep during a woman’s menses resulted in lower positive mood compared to non-menses. A good night of sleep, regardless of timing in the 28-day menstrual cycle, resulted in higher levels of positive mood.

“A woman’s menstrual cycle is often assumed to be associated with changes in mood, with menses characterized as a time of distress and negative mood. However, our findings indicate that menses status alone does not significantly alter either positive or negative mood states in healthy, young women without menstrual-associated complaints,” says co-author Sara Mednick, PhD, UCI cognitive sciences professor and director of the Sleep and Cognition Lab, in a release. “This is important as more than 90% of American women report only mild to moderate PMS, so we can generalize these results to the majority of women.”

Future research in the lab may examine the interplay of sleep, menstrual cycle, and mood as women age.

“The history of bias against women due to beliefs about menstrual cycle vulnerabilities have created glass ceilings for women in leadership positions. Our data suggests that this bias is an unfair characterization based on societally held beliefs rather than empirical evidence,” says Mednick in the release.

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