Quality sleep can be elusive, whether you struggle with racing thoughts, stress, or something else that keeps you from a solid night's rest. But for women, good sleep is even harder to come by, per a recent study published in Scientific Reports. Researchers found that females sleep less, wake up more often, and generally get "less restorative sleep" when compared with males.
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Many have attributed the disparity between the sexes to different lifestyle factors, but the new study revealed that it might go beyond who's waking up with the kids.
"In humans, men and women exhibit distinct sleep patterns, often attributed to lifestyle factors and caregiving roles," senior author Rachel Rowe, PhD, assistant professor of integrative physiology at the University of Colorado (CU) Bolder, said in a press release. "Our results suggest that biological factors may play a more substantial role in driving these sleep differences than previously recognized."
The noninvasive study used "ultrasensitive moment sensors" in specialized cages to track mice's sleep. The male mice slept about 670 minutes, or just over 11 hours, in a 24-hour period, an hour longer than their female counterparts. The male's extra sleep was in the non-rapid Eye Movement (NREM) phase, otherwise known as restorative sleep, where the body repairs itself.
Female mice also had more "fragmented" sleep periods and slept for shorter increments than males. (Mice sleep in a few-minute increments and then wake up to check their surroundings before returning to sleep.)
These sleep differences between the sexes have been observed in other animals, and Rowe said it makes sense when considering evolution.
"From a biological standpoint, it could be that females are designed to be more sensitive to their environment and be aroused when they need to be because they are typically the one who is caring for the young," Rowe said. "If we slept as hard as males sleep, we would not move forward as a species, right?"
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Still, other factors could be at play. Perhaps women actually need less sleep, or sex hormones and stress hormones like cortisol have more of an effect on women's sleep, researchers posit.
"For me, the question is: Are we creating too much stress for ourselves because we don’t sleep as much as our husband or partner and think our sleep is poor when actually that is a normal sleep profile for ourselves?" Rowe said.
Beyond some validation for women who may feel like their sleep is lackluster, the study also has important indications for future research. Even though the National Institutes of Health (NIH) now requires animal studies to look at "sex as a biological variable," there still appears to be a sex bias.
Mice are often used to test the safety and efficacy of new drugs, including sleep treatments, but there may not have been enough consideration for the difference between the sexes. Without an emphasis on this factor, it can lead to "flawed misinterpretations of data," first author Grant Mannino, CU graduate with degrees in psychology and neuroscience, added in the release.
"Bottom line: If females are underrepresented, drugs that work best for them may seem ineffective, or side effects that hit hardest may go unnoticed," the press release explains.
Researchers noted the need to look at both sexes equally, analyze male and female data separately, and take another look at studies that might not have had enough female representation.
"The most surprising finding here isn’t that male and female mice sleep differently," Rowe said. "It’s that no one has thoroughly shown this until now. We should have known this long before 2024."
