We all know that much of our physiology falls in line with an internal clock that controls our circadian sleep-wake cycle, core body temperature, and hormonal fluctuations. But our daily behavior, such as when we read the newspaper or first interact with another person, can also follow a daily pattern. Furthermore, the regularity of these daily activities in terms of how consistently they adhere to a certain time of day actually affects the quality of our sleep, a recent study found.

"For the majority of sleep outcomes, we found that completing activities at a regular time better predicted sleep outcomes than the actual time of day that activities were completed," Natalie Dautovich, lead study author and psychologist at the University of Alabama in Tuscaloosa, told Reuters Health. "For example, people reported better sleep quality and fewer awakenings at night when they were consistent in the time they first went outside."

Dautovich and colleagues had 50 younger adults (18 to 30 years) and 50 older adults (60 to 95 years) keep a diary for two weeks to complete daily assessments of their activities and sleeping patterns, such as total sleep time and sleep quality rating. Reporting in The Journals of Gerontology: Series B, they found that the variability in the timing of daily activities predicted sleep but that the results differed depending on the type of activity and age group.

Specifically, when activities such as starting work or eating dinner were undertaken at shifting times of the day, the older adults reported falling asleep more quickly or sleeping for a longer period of time at night. Conversely, irregular timing of going outside was associated with worse sleep outcomes for the older group. In fact, both the older and younger groups reported waking up at night and worse sleep quality when they varied the time of the day that they first went outdoors.

“Light exposure has long been recognized as the dominant ‘zeitgeber,’” the authors explain in the study, referring to an eternal cue that calibrates our biological rhythms. This, they add, serves to synchronize our sleep-wake cycle with the light-dark phase. “Dysregulation of this bright light exposure, especially first light exposure which plays a unique role in the circadian regulation of sleep, could understandably be associated with worse sleep.”

Despite older adults typically being the ones who follow a more routine and regular day-to-day existence, the study unexpectedly found that higher levels of variability in work and dinner activities was associated with better sleep for the older adults and worse sleep for the younger adults. “[I]t is possible that worse mood, and higher levels of stress and anxiety, often experienced by younger adult college students, could have contributed to poorer sleep outcomes for this age group,” the authors commented in the study.

As for the older adults sleeping better, they suggested that functional impairments that weren’t factored into the study could have created this inconsistency since prior research that found regularity in daily activity fostered better sleep patterns in older people.

Yet Dautovich didn’t discount the value that mixing up a daily schedule might have with regard to sleep. “"We know that good sleep at night is dependent in part on our drive to sleep, which is based on how active and alert we are during the day," she told Reuters. "Greater activity and levels of alertness during the day increase our need to sleep at night.”

Source: Dautovich, N., Shoji, K., McCrae, C. Variety is the Spice of Life: A Microlongitudinal Study Examining Age Differences in Intraindividual Variability in Daily Activities in Relation to Sleep Outcomes. J Gerontol B Psychol Sci Soc Sci (2013)