Variety is the Spice of Life: A Microlongitudinal Study Examining Age Differences in Intraindividual Variability in Daily Activities in Relation to Sleep Outcomes

Objective. 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. Measures. 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. Results. 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. Discussion. 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.