Impact on health outcomes associated with changing the clock one hour during fall and spring transitions in the Southern American Hemisphere.

STUDY OBJECTIVES:Changing the clocks seasonally is potentially harmful because it interferes with normal daytime activities. Studies aimed at quantifying this association are scant. The objective of this study was to determine the effects of one year's worth of changing the clocks (fall and spring transitions) on healthy young men located in the Southern American Hemisphere. METHODS:We performed an observational prospective study. Thirty healthy male university students were evaluated from two weeks before to two weeks after both the fall and spring transitions. We administered an overall sleep questionnaire, assessed quality of life, recorded 7-day wrist actigraphy, and had participants perform a Psychomotor Vigilance Task (PVT). We defined the one-hour clock change as the primary exposure and the change in PVT lapses of 500 ms or more in response time as our primary outcome. Changes were evaluated by the Wilcoxon rank test (significance: P<0.05). RESULTS:After the fall transition, we found a significant worsening in PVT performance (median [IQR] 9.9 [6.0-14.3] lapses of ≥ 500 ms in response time at baseline vs 16.8 [8.2-28.0] after transition; P<0.002). Additionally, we found a median loss of about one hour of total sleep time and time in bed after the fall transition. Furthermore, participants presented with insomnia. PVT performance was also affected after the spring transition (16.7 [10-23] vs 23 [12.2-32.2]; P<0.001). CONCLUSIONS:A decrease in performance in neurocognitive tests was found after both time transitions. The transition led to insomnia and a significant worsening of sleep variables.