Why do women sleep less and wake up more than men?

A new study has highlighted significant sleep differences between males and females, suggesting that biological factors have a greater influence than lifestyle in determining sleep patterns.

According to SciTechDaily , this finding prompts a re-evaluation of previous biomedical studies, which have often excluded women, leading to potential misinterpretations in the development of drugs and treatment effects related to sleep.

Gender differences in sleep patterns

According to a new study conducted by researchers at the University of Colorado Boulder (USA), women tend to sleep less, wake up more frequently, and experience less restorative sleep than men.

The study, published in Scientific Reports , highlights biological factors that may explain these differences and underscores the potential impact on biomedical research, which has largely focused on men.

' In humans, men and women have distinctly different sleep patterns, which are often attributed to lifestyle factors and family caregiving roles ,' explains Rachel Rowe, lead author and associate professor of integrative physiology.

Women tend to sleep less, wake up more frequently and experience less restorative sleep than men - (Photo: Reuters).

'Our findings suggest that biological factors may play a much more important role in driving these sleep differences than previously recognized ,' she added.

Sleep research has exploded in recent years, with thousands of animal studies exploring how sleep deprivation affects the risk of diseases like diabetes, obesity, Alzheimer's, and immune disorders — and, conversely, how these diseases affect sleep.

Meanwhile, mice are often the first subjects tested to see how new drugs, including sleep medications, work and what side effects they have. However, research suggests that many results may be skewed by a lack of female representation.

"Essentially, we found that the most commonly used mouse breed in biomedical research has sex-specific sleep behaviors, and that not accounting for these differences can easily lead to misinterpretations of the data," said study author Grant Mannino.

The Importance and Impact of Sleep Research

In this non-invasive study, the authors used specialized cages with ultra-sensitive motion sensors to assess the sleep patterns of 267 mice coded 'C57BL/6J.' Male mice slept a total of about 670 minutes every 24 hours, about 1 hour more than female mice.

That extra sleep is non-rapid eye movement (NREM) sleep — the restorative type of sleep when the body heals itself.

Mice are nocturnal and have a "polyphasic" sleep pattern - sleeping for a few minutes, then waking up to survey their surroundings and falling back asleep. Research shows that female mice's sleep is more fragmented.

Similar sex differences have been seen in other species, including fruit flies, rats, zebrafish, and birds. This makes evolutionary sense.

"Biologically, it's possible that females are designed to be more sensitive to their surroundings and wake up when necessary because they're typically the ones caring for their young," Rowe explains . " If women slept as deeply as men, we wouldn't have evolved as a species ."

Stress hormones like cortisol contribute to alertness, and sex hormones may also play a role. For example, women often report worse sleep during the time of their menstrual cycle when estrogen and progesterone levels are lowest.

Gender bias persists in research

In 2016, the US National Institutes of Health began requiring scientists to consider 'sex as a biological variable' when applying for funding for animal research. But research shows that gender bias persists, and it can have real consequences.

'We hope our study will prompt scientists to include both sexes equally in their studies, analyze data separately for men and women, and reevaluate previous studies that have underrepresented women ,' Rowe concluded.

If women are underrepresented, the most effective drugs for them may appear ineffective, or the most severe side effects may go undetected.

'The most surprising finding here isn't that male and female mice sleep differently, it's that no one has really demonstrated this thoroughly until now,' says Rowe. 'We should have known this long ago, before 2024. '