Abstract
The relative importance of mean timing of daily activities versus intraindividual variability in the timing of daily activities in relation to health outcomes such as sleep has yet to be established. Furthermore, age-related changes in sleep could affect this relationship. The study objective was to examine the extent that intraindividual variability in the timing of daily activities is associated with sleep outcomes in younger and older adults. A microlongitudinal observational study design was used with 14 consecutive days of diaries in community-dwelling younger and older adults. 50 younger and 50 older adults completed daily assessments of activities and sleep. Three activities (going outside, starting work, and eating dinner) and 5 sleep (sleep onset latency, wake time after sleep onset, number of awakenings, total sleep time, and sleep quality rating) variables were used in the analyses. Hierarchical regressions revealed variability in the timing of daily activities significantly predicted sleep, beyond mean timing of activities, for 4 of 6 models. Results differed depending on the type of activity and age group. Intraindividual variability, not mean timing of daily activities, best-predicted sleep outcomes. Variability was associated with positive sleep outcomes for older, but not younger adults.
Highlights
Substantial research has been devoted to the study of underlying physiological circadian rhythms, it can be argued that behavioral circadian rhythms warrant further interest as they are the rhythms most salient to us and, are amenable to change (Monk, 2010)
BSOL = initial time from lights out until sleep onset; wake time after sleep onset (WASO) = time spent awake during the night after initially falling asleep; number of awakenings (NWAK) = the number of times you awaken during the night; total sleep time (TST) = total time spent in bed minus sleep onset latency (SOL) and WASO until final wake up; and sleep quality rating (SQR) = a 5-point rating of the quality of sleep ranging from poor to excellent
The variables of interest for the present study that were derived from the sleep diary included: sleep onset latency (SOL; initial time from lights out until sleep onset); wake time after sleep onset (WASO; time spent awake during the night after initially falling asleep); number of awakenings (NWAK; the number of times you awaken during the night), total sleep time (TST; total time spent in bed minus SOL and WASO until final wake up); and sleep quality rating (SQR; a 5-point rating of the quality of sleep ranging from poor to excellent)
Summary
The main finding from the present study is that intraindividual variability in the timing of daily activities better predicted sleep outcomes compared to the mean timing of activities for four out of the six significant models. Of the two models with mean timing significantly predicting sleep outcomes, going outside and beginning work later in the day was associated with longer total sleep time for both younger and older adults. Higher levels of intraindividual variability in the timing of work and dinner activities was associated with poorer sleep outcomes for younger adults but not for older adults. Variability in activities not associated with bright light such as starting work or eating dinner was associated with better sleep outcomes for older adults The implications for these findings include a need to assess the regularity of daily activities in the treatment of poor sleep. Age differences were found in the relationship between intraindividual variability of daily activities and sleep outcomes with intraindividual variability appearing to be more adaptive for older adults
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