Towards a balanced and ethically responsible approach to understanding differences in sleep timing : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Public Health at Massey University, Sleep/Wake Research Centre, Wellington Campus, New Zealand
The circadian clock defines physiologically optimal times for sleeping, which vary along a continuum of circadian phenotypes from morning- to evening-type. Although different ‘chronotypes’ can be discriminated reliably by the Morningness/Eveningness Questionnaire (MEQ), there is little published information on their prevalence. The timing of sleep is also heavily influenced by societal norms. However, the relative contribution of circadian physiology versus psychosocial factors is unknown.
This thesis took a multidimensional approach to investigating preferred sleep timing within the general population of New Zealand (30-49 years). A New Zealand version of the MEQ was mailed to a random stratified sample of 5,000 adults living in the Wellington region (55.7% response rate). Using scoring criteria for middle-aged adults, approximately 25% of the population were morning-types and 25% were evening-types.
The sleeping patterns of 15 morning- and 16 evening-types were monitored using actiwatches and sleep diaries. Morning-types slept significantly earlier, but there were no differences in sleep duration or quality. Both chronotypes showed evidence of using the weekend to catch-up on sleep, although this was more evident among evening-types.
Differences between chronotypes were also investigated using the endogenous melatonin rhythm as a circadian phase marker. The timing of the melatonin rhythm was earlier among morning-types, with the difference being greater for melatonin onset, than offset. However, differences between weekday versus weekend sleep explained more of the variability in sleep timing that did circadian phase.
Understanding the genetic differences in the circadian clock is evolving rapidly. While this is of particular scientific interest, little consideration has been given to the ethical implications of this type of work. In the final study, a Kaupapa Māori framework was used to explore Māori hopes and concerns for genetic research in Aotearoa/New Zealand. Thematic analysis indicated that Māori are not anti-science, however there is an urgent need for ethical guidelines that uphold and respect the values of Māori society.
This thesis argues that sleep is a major public health issue for New Zealand. However, a number of challenges must be met to ensure that new scientific knowledge meets the needs and expectations of the community.