Shifts in Sleep-Wake Cycles Affect Women More than Men

The Surrey Sleep Research Center at the University of Surrey has performed a new study that shows shifts in the sleep-wake cycles (circadian rhythm) has a greater impact on women than it does on men.  This study was published in the journal, Proceedings of the National Academy of Sciences (PNAS).

The study involved the assessment of the participants’ performance who were placed on 28-hour days with their circadian rhythm (sleep-wake cycle) shifted out of phase with the brain.  The cognitive performance, as mentioned, was more affected in women than in men.  This research indicates that there are significant implications for women who work nightshift hours, especially nurses, police officers, and security guards.

In this study, performed at the Surrey Clinical Research Centre, the researchers utilized a controlled environment without the natural light-dark cycles and placed 18 women and 16 men on a 28-hour day.  This was an effective way to desynchronize the brain’s 24-hour circadian clock, which is similar to a shiftwork scenario or jet lag.

During the awake period, participants were asked to perform a wide range of tests every three hours.  These included tests on mood and effort, self-reported assessments on sleepiness, as well as objective scales of cognitive performance.  This last included measurements of motor control, memory, and attention span.  Throughout this study, an EEG (electroencephalogram) to look at brain electrical activity, was monitored during the sleep states.  In both women and men self-reported assessments of sleepiness and cognitive function, the results showed that they were more sensitive to the circadian clock and the effects of awake time than the objective tests of performance.  Of critical note, however, is that women’s performance, more so than men’s, was strongly affected by the circadian clock shift.  It was such that women were more impaired cognitively during the early morning hours, which generally coincides with the end of a night shift in the real world.

Dr. Nayantara Santhi, co-author of the study out of the University of Surrey, reported that for the first time, this study shows that the challenges of a shifted circadian clock affects women and men’s performance very differently.  The findings suggest that there are significant cognitive impairments and changes in mood in those who do shiftwork.  Extrapolating these results shows that women are affected more negatively than men when it comes to this type of work.

Professor Derk-Jan Dijk, senior author of the study, reports that the results actually indicate circadian rhythmicity affects the brain’s function in both men and women, albeit differently in quantitative measures.  Professor Dijk also reports that, overall, these findings illustrate the importance of including both sexes in sleep studies, as well as the importance of using a wider range of objective and subjective indicators of brain function in order to get a better understanding of how circadian rhythm affects each group.


Author:Rachael Herman is a professional writer with an extensive background in medical writing, research, and language development. Her hobbies include hiking in the Rockies, cooking, and reading.


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