0032 Some Sleep and Circadian Outcomes Following the Spring Daylight Saving Time Transition Among a Cohort of Urban/Suburban Subjects

Abstract Introduction Periodically, concerns are raised about the effects of societally-mandated changes to and from daylight saving time (DST) on circadian and sleep-related outcomes. Arguments for or against changes to local clock time are sometimes based on limited outcome measures. The present study examined a range of circadian and sleep-related outcome measures with the aim of better understanding the spring DST transition’s impact on circadian phase markers, sleep outcomes, and subjective sleepiness among a cohort of urban/suburban subjects living their normal lives. Methods Twenty healthy adult subjects (16F/4M, mean age 42 y [SD 13]) following their daily routine participated in the study, which ran from 26 February 2024 to 3 May 2024. Personal, calibrated light exposure devices were continuously worn during waking hours and wrist actigraphs were worn continuously except during bathing. The personal 24-h light-dark and the wrist activity-rest cycles were recorded for phasor analysis to assess circadian entrainment. The personal light-dark exposure patterns were used to predict minimum core body temperature (CBTminp). The actigraph data were used to calculate mid-sleep. Dim light melatonin onset (DLMO) was assessed just before the transition to DST and 2 weeks after the transition. Subjects reported their levels of subjective sleepiness four times each day. Results 1) Local clock times of mid-sleep and of DLMO were not affected by the DST transition but CBTminp was delayed after the DST transition. 2) The synchrony between the 24-h light-dark exposure pattern and the 24-h activity-rest pattern was not affected by the DST transition. 3) Karolinska Sleepiness Scale score was heightened in the mornings just following the transition, but by the end of the first week morning sleepiness returned to the same levels as those before the transition. Conclusion 1) The spring transition to DST had modest effects on most circadian/sleep-related measures. 2) The temporal relationship between circadian phase markers was altered after the transition to DST. 3) Circadian entrainment was not affected by the DST transition. 4) Relatedly, subject activity was correlated with available light both before and after the DST transition even though the subjects spent most of their time indoors. Support (if any)