Effects of Circadian versus Psychosocial Factors on Sleep Timing
This study recorded the sleep/wake patterns (wrist actigraphy for two weeks) of 14 morning-types and 14 evening-types from a community-based sample of 30 to 49-year-old New Zealanders (Horne-Ostberg Morningness/Eveningness questionnaire). Participants then came into the laboratory for a 17-hour constant routing protocol to monitor the evening melatonin rise as a marker of the circadian pacemaker rhythm. Compared to morning types, evening types had later sleep start and end times on weekdays and on weekends, and later dim light melatonin onset (DLMO).
The estimated contribution of the DLMO to the mean observed differences in sleep timing were: on weekdays 39% for sleep start times and 49% for sleep end times; and on weekends, 41% for sleep start times and 34% of sleep end times. We concluded that differences in sleep timing between morning types and evening types were much greater than would be predicted on the basis of the independent contribution of the difference in DLMO on both weekdays and weekend days. The timing of sleep in daily life involves complex interactions between physiological and psychosocial factors, which may be moderated by age in adults aged 30–49 years.
Funding: Health Research Council of New Zealand, Lottery Health Research.
Dr Hererepine Sarah-Jane Paine (2006). Towards an Ethically Responsible Approach to Understanding Differences in Sleep Timing. PhD thesis, Massey University.