Synchronization to daylight saving-time: Circadian organization of wrist temperature and rest/activity rhythms

Objectives: Besides being an administrative effort directed to decrease electric energy expenditure in industrialized countries, daylight saving-time (DST) interacts with Human organism and may represent a potential temporal challenge. Therefore, the aim of the present work is to analyze the interaction between the transitions to and from DST on internal temporal organization. Methods: Five subjects were submitted to concomitant assessment of wrist temperature and actigraphy for two periods of 20 days comprising the transitions to and from DST. Data were extracted and amplitude, acrophase and mesor were estimated by Cosinor method. Results: Mesor and amplitude of the studied rhythms remained unchanged during both transitions. Acrophases of wrist temperature and rest-activity rhythms advanced in distinct magnitudes in the transition to DST. Leaving DST to local time, however, only wrist temperature showed a marginally phase delay. Discrepancies regarding phase shifts changed the phase relationship between the studied rhythms, resulting in an increase of 67 minutes in phase angle in the transition to DST and a decrease of 115 minutes in the transition from DST to regular local time. Conclusions: DST evokes acute changes in phase relationship between wrist temperature and rest-activity rhythms, representing a significant temporal challenge, thus explaining the interaction among DST transition, sleep physiology and incidence of traffic and workplace accidents.