O070 Objective impact of daylight-savings time shifts on sleep: a global-scale study

Abstract Introduction The twice-yearly transitions between standard time and daylight-savings time (DST) introduce mild circadian misalignments, which are associated with disrupted sleep, and increased risks for adverse public health and safety consequences. Previous evidence is based on self-reported data, limited geographical locations, and relatively small sample sizes. Here, we quantify the acute impact of seasonal clock time changes on objective measures of sleep in a large global sample. Methods Data were collected from users of a validated under-the-mattress sleep sensor between March 2018 and September 2023, located across 27 countries covering 36 different clock-timed regions (>500 users/region) where DST changes occur. Total sleep time and sleep offset timing on the dates of clock adjustment were compared to the Sunday immediately preceding each time shift, using linear mixed models with a random intercept for time zone. Results Data from >60,000 individuals were analysed (82% males, age 49±13 years). Setting the clock forward was associated with a reduction in sleep duration of 13.7 minutes (95%CI 9.1 to 16.1), and a sleep offset timing delay of 33.1 minutes (28.9 to 37.4). The end of DST (clock backwards) was related to longer sleep durations, increasing by 9.84 minutes (6.9 to 12.78), and earlier sleep offset times by 33.6 minutes (29.1 to 38.1). Conclusions This large-scale global study shows that clock time adjustments derived from daylight saving regulations have immediate repercussions on objective sleep duration and timing. These findings may help inform the ongoing policy debate of the impact of DST on sleep and associated consequences.