In recent years, sleep research has seen substantial development, with thousands of animal studies exploring how insufficient sleep increases the risk of various conditions like diabetes, obesity, Alzheimer’s, and immune disorders. In addition, mice have frequently been the first to be tested in humans to find out whether new drugs like medications for sleep do and would have side effects.
A study report published in the Journal Scientific Reports aims at clarifying and explaining the differences between men’s and women’s sleep, long focus on the male version of species. Senior author Rachel Rowe is an assistant professor of integrative physiology and said that men and women have different sleep patterns, which are often attributed to lifestyle factors and caregiving roles. “Our results indicate that biological factors may be more important drivers of these sleep differences than previously appreciated.”
“We found out that the mouse strain that is most commonly used in biomedical research has sex-specific sleep behavior and if you don’t consider the sex differences, you can easily misinterpret the data,” said Grant Mannino, department of psychology and neuroscience, University of Colorado–Boulder, USA. To conduct the study, the authors used specialized cages lined with ultrasensitive movement sensors to test the sleep patterns of 267 “C57BL/6J” mice (males = 140 and females = 127). Female mice slept 645 minutes total over 24 hours, compared to 670 minutes for males. That extra sleep was not rapid eye movement (NREM) sleep, the sort of sleep that helps the body fix itself.
They’re ‘polyphasic sleepers,’ nocturnal mice that sleep a minute or so and then raise their heads to check out the scene before nodding back off. The study found that females’ sleep bouts, essentially, their sleep, are even shorter, ‘we sleep even more fragmented than the males,’ said Guy Peck, associate professor of biology at TEV Colleges. ‘If you slept as hard as males sleep, we would not move forward as a species, right?’ This probably has to do with stress hormones like cortisol (which makes you wakeful) as well as sex hormones. Consider, for instance, women reporting worse sleep during the period of their cycle when estrogen and progesterone are at their lowest levels. It was speculated that females need less sleep naturally. The authors hope their findings prompt further research on the underlying biological differences.
In 2016, as part of a national initiative to require consideration of ‘sex as a biological variable,’ the National Institutes of Health started requiring scientists seeking funding for animal studies to account for sex. There is progress, but the research has also shown that sex bias still exists. The authors found that it can have real consequences. ‘The bench to bedside pipeline is decades and there’s a long way to go sometimes from animals until it goes into clinical trials, things that work in animals will fail in humans.’ ‘Is it taking so long because it’s not considered sex enough? ‘said Rowe and also said “The most surprising finding here isn’t that male and female mice sleep differently. I guess nobody had shown this before.”
The authors recommend that researchers include both sexes equally whenever possible and that when they analyze data separately for each sex, they reevaluate previously conducted studies that involved only one sex.
Reference: Mannino GS, Green TRF, Murphy SM, et al. The importance of including both sexes in preclinical sleep studies and analyses. Sci Rep. 2024;14:23622. doi:10.1038/s41598-024-70996-1
