Public Release: 

New study finds shifted sleep-wake cycles affect women more than men

University of Surrey

  • Study involved assessment of performance in participants being placed on 28-hour days to shift the sleep-wake cycle out of phase with the brain (circadian) clock
  • Performance was more affected in women than in men
  • Research has significant implications for female nightshift workers such as nurses, security guards and police officers

A new study from the Surrey Sleep Research Centre at the University of Surrey, published today in the journal PNAS (Proceedings of the National Academy of Sciences) has found that shifted sleep-wake cycles affect men and women's brain function differently.

Researchers placed 16 male and 18 female participants on 28-hour days in a controlled environment without natural light-dark cycles, at the Surrey Clinical Research Centre. This effectively desynchronised the sleep-wake cycle from the brain's 24-hour (circadian) clock, similar to jet lag or a shiftwork scenario.

Every three hours during the awake period, participants performed a wide range of tests, including self-reported assessments of sleepiness, mood and effort, and objective tests of cognitive performance which included measures of attention, motor control and working memory. Brain electric activity (EEG) was monitored continuously during sleep. The results revealed that in both men and women self-reported assessments were more sensitive to the effects of time awake and circadian clock than the many objective measures of performance. However, crucially, the circadian effect on performance was significantly stronger in women than in men such that women were more cognitively impaired during the early morning hours, which in the real world typically coincides with the end of a night shift.

Co-author, Dr Nayantara Santhi from the University of Surrey, said, "We show for the first time that challenging the circadian clock affects the performance of men and women differently. 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."

Senior author, Professor Derk-Jan Dijk, continued, "These results show that in both men and women circadian rhythmicity affects brain function and that these effects differ between the sexes in a quantitative manner for some measures of brain function."

"Overall the findings illustrate how important it is to include both men and women in research studies and to use a wide range of subjective and objective indicators of brain function," added Professor Dijk.

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Find out more about the Surrey Sleep Research Centre at http://www.surrey.ac.uk/fhms/research/centres/ssrc/ and for programmes available within the field of Biosciences and Medicine.

Media enquiries:

Peter La
Media Relations Office at the University of Surrey
Tel: 01483 689191
E-mail: p.la@surrey.ac.uk

Notes to Editors:

The research was funded by the Biotechnology and Biological Sciences Research Council.

About the University of Surrey

The University of Surrey is one of the UK's leading professional, scientific and technological universities with a world-class research profile and a reputation for excellence in teaching. Ground-breaking research at the University is bringing direct benefit to all spheres of life - helping industry to maintain its competitive edge and creating improvements in the areas of health, medicine, space science, the environment, communications, defence and social policy. Programmes in science and technology have gained widespread recognition and it also boasts flourishing programmes in dance and music, social sciences, management and languages and law.

In addition to the campus on 150 hectares just outside Guildford, Surrey, the University also owns and runs the Surrey Research Park, which provides facilities for 110 companies employing 2,750 staff. The University of Surrey was recently named University of the Year by the Times and Sunday Times, both overall and for 'Student Experience', and has achieved a top-ten ranking in all three major national university league tables.

For more information about the University and its work, visit http://www.surrey.ac.uk

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