Zeitgebers and their association with rest-activity patterns

ABSTRACT

Zeitgebers such as light, eating and physical activity provide input to the circadian clock. Chronic circadian misalignment is associated with significant adverse health effects. An improved understanding of the impact of the timing of zeitgebers on the stability of 24-hour rest-activity rhythm in free-living settings may identify behavioural and environmental intervention targets. A total of 133 healthy adults, aged 21–60 years, wore a wrist actigraph for 7 consecutive days. We applied a non-parametric analysis to activity counts to derive rest-activity patterns. We administered a questionnaire through a smartphone app to collect self-reported timing of light exposure, eating episodes and physical activity. To assess the relationship between timing exposures (first and last exposure to outdoor light, first exposure to indoor light, last eating episode, first eating episode, morning physical activity proportion, evening physical activity proportion) and rest-activity or sleep outcomes (bedtimes, total sleep time, inter-daily stability, intra-daily variability, L5 and M10 midpoint), we first calculated Spearman correlations, using the false discovery rate method to control for multiple comparisons. From those significant associations, we then fit regression models adjusting for age, sex, race, household income, education level, study site, body mass index, as well as physical activity. Finally, we tested for interaction between chronotype and each timing-related exposure and stratified the analysis by morning type. All zeitgebers, except for evening physical activity proportion, were correlated with at least four of the seven sleep and rest-activity outcomes. In adjusted analysis, later timing of first (after 6:30 to 7:45 AM versus earlier) and last exposure to indoor light (after 11:00 PM versus earlier) and first (after 7:45–9:45 AM versus earlier) and last eating episode (after 8:00–09:00 PM versus earlier) were associated with a shift of 0.60–1.39 hours to later bedtimes, M10 and L5 midpoints (i.e. timing of peak activities or inactivities). Later timing of first exposure to outdoor light (after 09:30 AM versus earlier) was also associated with 0.51 (95% CI: 0.19 to 0.83) hours longer total sleep time. Higher morning physical activity proportion (> 33%) was associated with 0.95 (95% CI: −1.38 to −0.53) hours earlier in-bed time and 0.69 (95% CI: −1.14 to −0.24) hours earlier out-of-bed time, 0.92 (95% CI: −1.41 to −0.42) hours earlier M10 and 0.96 (95% CI: −1.42 to −0.49) min earlier L5 midpoint. The results did not change substantially with further adjustment for total activity. There was a significant interaction between morning chronotype and first eating episode with rest-activity patterns (p < 0.05), with first eating episode associating with timing of activities only in non-morning type adults. Timing of zeitgebers was associated with sleep and rest-activity patterns, including bedtimes, L5 and M10 midpoint. Future research should evaluate the impact of manipulating zeitgebers on both circadian rhythms and health outcomes.

KEYWORDS:

• Actigraphy
• rest-activity patterns
• physical activity

Disclosure Statement

Jonathan Mitchell was supported by NIH grant K01 HL123612 (NHLBI). Catherine Marinac was supported by the National Cancer Institute under award number 1F31 CA183125 and F32CA220859 by an American Cancer Society Postdoctoral Fellowship under award number PF-17-231-01-CCE. Peter James was supported by National Cancer Institute grant K99 CA201542. Mirja Quante was supported by a scholarship from the Tuebinger Program for the Advancement of Women in Science. Sara Mariani was supported by NIH grant R24HL114473 (NHLBI). The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Additional information

Funding

This work was supported by the National Cancer Institute [1F31 CA183125, K99 CA201542, U01 CA116850, U54 CA155435, U54 CA155496, U54 CA155626, U54 CA155850];National Heart, Lung, and Blood Institute [K01 HL123612,R24HL114473]. American cancer society (PF17-231-01-CCE) and the Tuebinger Program for the Advancement of Women in Science.