By now you probably know that a sleep-deprived brain is no good. It gets super emotional, craves junk food, and starts to shrink, and those are just a few of the health problems sleeplessness causes. Less well known is that lack of sleep affects men and women differently, and scientists are just starting to discover how.

Research has shown that the body’s circadian rhythm partly regulates sleep. Not unlike a Rolex, the biological clock helps humans coordinate behavior with the time of day: If the sun is out, they’re up and ready for work; not long after dark falls, they’re getting ready for bed. A group of nerve cells found nearly everywhere in the body and brain are in charge of these cues. When it stops working correctly, circadian timing can get knocked out of order. Mood disorders, reduced brain function, depression, and Alzheimer’s disease have all been linked to inadequate shut-eye.

While some studies have shown these disorders are more common in women than men, women are underrepresented in both circadian and sleep research, according to a new study published in the Proceedings of the National Academy of Sciences. That these effects depend on the person has been documented to some extent, the study authors said, but sex differences specifically related to the internal clock have not.

For their study, they placed 16 male and 18 female participants on 28-hour days at the Surrey Clinical Research Center in the United Kingdom, a controlled environment without natural light-dark cycles. Essentially, the room is designed to affect the brain and internal clock the way jet lag or working the night shift does. When awake, participants were asked to complete a series of assessments every three hours, including self-reported measures of sleepiness and mood as well as cognitive tests on motor control and memory. Once asleep, researchers performed an EEG to detect electrical activity in the brain.

Results confirmed that the sleep-wake cycle and circadian phases modulate almost all aspects of waking function, with men’s and women’s disrupted clocks resulting in similar, adverse outcomes. In women, however, cognitive performance seemed to suffer a bit more compared to men. Their brain function was reduced during early morning hours, which could have a significant implication for women who work the night shift such as nurses, security guards, and police officers.

“We show for the first time that challenging the circadian clock affects the performance of men and women differently,” study co-author Dr. Nayantara Santhi, of the University of Surrey, said in a press release. “Our research findings are significant in view of shiftwork-related cognitive deficits and changes in mood. Extrapolation of these results would suggest that women may be more affected by night-shift work than men."

Santhi and her colleagues cited separate research that shows women face increased risk of occupational injuries during extended work shifts and non-standard and changing hours. This could reflect the added demand on women of social factors like family and childcare responsibilities. In fact, a 2013 study suggested that women need more sleep than men for biological reasons and because of mental energy expenditure — women tend to multitask more than men. This may cause women to work longer hours and need more time to recover from the day than men. The authors of that study, though, noted that men who have a complex job and are involved in a lot of decision-making may need more sleep than the average male, too.

That said, Santhi’s study was designed primarily to look at sleep and circadian rhythms, not sex differences, the authors wrote. Many of the participants’ tasks also had time limits, something that might work in favor of men more than women. The women’s menstrual cycles may have also played a role in reduced brain function, as the process is known to affect attention, emotion, response to reward, and the ability to complete spatial tasks.

Source: Santhi N, Lazar AS, et al. Sex Differences In the Circadian Regulation of Sleep and Waking Cognition In Humans. Proceedings of the National Academy of Sciences. 2016.