Circadian Biomarkers Before and After the Transition to Spring Daylight Saving Time

Periodically, concerns are raised within the research community about the effects on circadian and sleep-related outcomes resulting from changes to and from daylight saving time (DST). To better understand these concerns, we collected varied circadian and sleep-related outcomes from healthy individuals immediately before and after the spring DST transition.

Subjects wore calibrated, personal light sensors that measured light exposure (amount, duration, time) and wrist actigraphs to quantify the synchrony between the 24-hour light-dark exposure and the 24-hour activity-rest cycles. Sleep onset, offset, and time in bed were obtained from the wrist actigraphs. Dim light melatonin onset (DLMO) was also measured before and after DST transition. Predicted minimum core body temperature (CBT _min ^p ) times were calculated from the light exposure data. Karolinska Sleepiness Score (KSS) ratings were collected four times a day. Health-related outcomes were not examined.

The spring DST transition had modest (statistically insignificant) effects on the weekly averages of time in bed (≤ 21 min), subjective sleepiness (KSS < 0.48), and the synchrony between the light and activity cycles (phasor magnitude ≤ 0.08 units). After the transition to DST, CBT _min ^p was slightly delayed, whereas DLMO and mid-sleep were slightly advanced.

For this cohort, the spring transition to DST had little if any effect on a variety of circadian and sleep-related outcomes. The transition appears to have caused a small disassociation in the relative timing of the circadian phase markers, which may or may not be of some significance for health and wellbeing.