A new study from the University of Surrey reports that changes in sleep-wake cycles have a stronger impact on women than men, greatly affecting their cognition and accuracy when performing cognitive tasks


When is the last time you got a full eight hours of sleep? If you can’t recall it off the top of your head, you might be in some trouble. Current scientific journals are filled with studies linking sleep deprivation and problems with proper functioning (like alertness, mood, attention, and memory). Studies have successfully connected sleep duration and a number of serious health problems, including obesity, diabetes, hypertension, and depression. Drowsiness in sleep-deprived drivers is likely the cause of more than 100, 000 crashes, 71, 000 injuries and more than 1, 500 deaths each year. More than 40 million Americans report having sleep problems; and yet, many of us still do not get a good night’s sleep.

Despite habitually staring at the clock on the computer screen (waiting for it to hit 5:00pm to clock out), our bodies have their own biological clock: a circadian clock. Circadian clocks drive our circadian rhythms, any biological process that displays a built-in oscillation of about 24 hours. Circadian rhythms are important in determining the sleeping and feeding patterns of all animals, including humans. They regulate our sleep-wake cycles (the cycle of sleeping and wakefulness) through the release of hormones; but these rhythms can be disrupted by environmental factors. Stress, drugs, shift work, and jet lag can all impact our circadian rhythms, and therefore our sleep-wake cycles.

Sex differences in human circadian rhythms have been previously noted; women reportedly have earlier timing and longer duration of sleep, more slow-wave (deep) sleep, and shorter circadian periods of body temperature and melatonin (sleep hormone) rhythms. Although sex differences in circadian rhythms have been noted, the impact of a disturbed sleep-wake cycle on men versus women is not clearly understood.

A new study published in Proceedings of the National Academy of Sciences has reported that there may in fact be a difference in the impact of disturbed sleep-wake cycles on both sexes. 16 men and 18 women were recruited for this study, and researchers forcibly desynchronized their circadian rhythms. Participants were placed on 28-hour days in a controlled environment without natural light-dark cycles. They were instructed to stay awake longer than normal, and were asked to perform tasks at adverse circadian phases (times when we are normally asleep). Researchers then observed how a changed circadian rhythm impacted self-reported levels of sleepiness, cognition, and accuracy, speed and effort when completing cognitive tasks.

Researchers determined that disrupting sleep-wake cycles had a larger impact on the women participating in the study. Accuracy deteriorated more in the women than in the men, but women were less likely to report being sleepy. As well, sleep deprivation had a bigger impact on the women’s effort and cognition, especially during the early morning hours. There was no difference in speed for men and women when completing the tasks.

Researchers suggest that this study could explain why women are more likely to be at risk for occupational injuries during extended work shifts, nonstandard shifts and changing shifts. The increase in cognitive impairment during the early morning hours coincides with the end of a typical over-night shift. Researchers report that these findings could have large implications for women who have night shifts, who have reoccurring shift changes, or who are experiencing jetlag.




Written By: Alexandra Lostun, BSc

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