Rethinking the sleep-health link☆
Introduction
Sleep characteristics such as duration, quality, timing and variability have been associated with a wide range of health outcomes, including cognitive,1 psychosocial2 and cardiometabolic health,3 as well as specific conditions such as Type 2 diabetes,4 cardiovascular disease,5 stroke6 and obesity.7
Accordingly, sleep is increasingly being recognized as a central concern for population health. Heffron,8 for example, argues that “sleep is one of the three pillars (diet, exercise and sleep) of a healthy lifestyle”, while Perry and colleagues9 emphasize the need to consider sleep as “being as critical to health as diet and physical activity”. In line with these messages, the American Academy of Sleep Medicine, the Centers for Disease Control and Prevention, and the Sleep Research Society partnered on the Healthy Sleep Project, in an effort to improve public health by promoting healthy sleep.8 The initiative included the Sleep Well, Be Well campaign, which highlighted the importance of adequate and consistent sleep, avoiding alcohol and caffeine before bed and seeking medical advice for sleep problems. Similarly, the (American) National Sleep Foundation has recently proposed the “Sleep Health Index”, which attempts to capture the construct of sleep health based on multiple sleep characteristics.10 These two approaches represent a shift in the conceptualisation of sleep in relation to population health.
Historical attempts to improve sleep largely focused on sleep duration.11 In contrast, conceptualizing sleep as a multidimensional construct12 and treating sleep holistically recognizes that sleep duration, as well as other sleep characteristics such as quality, timing and variability, may all be important for health.8, 12 Sleep has also traditionally been considered as divorced from the 24-hour day. However, any change in sleep duration will necessarily entail changes in the other time-use components of that day. Conceptualizing sleep as a component of 24-hour time use recognizes that sleep duration does not occur in isolation from other time-use domains (i.e. sedentary time and physical activity), which are also known to affect health.13 While these two approaches may seem contradictory, they each provide a complementary and unique insight into the role of sleep.
In spite of these new perspectives, our current understanding of sleep stems from studies that examine the association between an individual sleep characteristic (often sleep duration) and a given health outcome. To date, relatively few studies have considered sleep as a multidimensional construct or as a component of daily time use. There is also no agreed framework for considering sleep in these new ways.
The purpose of this paper is, therefore, to present a rationale and a methodology for conceptualizing sleep both as a multidimensional construct and as a component of daily time use. Specifically, we discuss why sleep should be considered from these perspectives and describe statistical techniques for the analysis of sleep data within this new paradigm.
Section snippets
Sleep as a multidimensional construct
Over the years, there has been increasing awareness that sleep duration may not be the only characteristic contributing to optimal health and well-being. It has been recognized that other characteristics of sleep, such as sleep quality, timing and variability, may all play an important role.12 Indeed, a Scopus database search conducted on the 25th of July 2017 reveals that the number of hits returned for publications with title or abstract key words containing a specific sleep characteristic
Sleep duration as a modifiable component of time use
Just as sleep is complex and multidimensional in nature, with characteristics of sleep not occurring in isolation, sleep does not occur independent of other components of time, but rather is a component of the 24-hour use-of-time profile. If sleep duration shortens, time awake lengthens and must be filled with other activities, in terms of energy expenditure, these activities may be sedentary (e.g. sitting, watching television until late) or physically active (e.g. waking up early to go for a
Conclusion
Interventions and public policies to improve population sleep are still in their infancy. There is a clear need to move from a focus on individual sleep characteristics and health outcomes towards an integrated approach to sleep as part of a healthy lifestyle. Sleep should be reconceptualised both as a multidimensional construct and as a modifiable component of a 24-hour day. Such an understanding is important for increasing the effectiveness of public health efforts that aim to modify sleep to
Conflict of interest
There are no conflict of interests to declare.
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Funding/acknowledgements: Dorothea Dumuid was supported by Australian Government Research Training Program Scholarships. Tea Lallukka was supported by the Academy of Finland (grant numbers #287488, #294096). Yu Sun Bin was supported by a 2017 Career Development Award from the Sleep Research Society Foundation. Melissa Wake was supported by Australian National Health & Medical Research Council Senior Research Fellowship 1046518 and by Cure Kids New Zealand. Research at the Murdoch Children's Research Institute.