Health and legal time

Millions of shift workers in the U.S. face an increased risk of depression, cancer, and metabolic disease, yet individual responses to shift work vary widely. We find that a conserved biological system of morning and evening oscillators, which evolved for seasonal timing, may con…

Millions of shift workers in the U.S. face an increased risk of depression, cancer, and metabolic disease, yet individual responses to shift work vary widely. We find that a conserved biological system of morning and evening oscillators, which evolved for seasonal timing, may contribute to these interindividual differences. In this study, we analyze seasonality in medical interns working shifts, revealing that summer-winter variation correlates with increased circadian misalignment after shift work. Mathematical modeling suggests that seasonal timing influences the rate of adaptation to new schedules, predicting differential effects on morning and evening oscillators. Additionally, we examine genetic polymorphisms linked to seasonality in animals and find that human variants can impact how quickly circadian rhythms respond to schedule changes. Based on our findings, we hypothesize that the vast interindividual differences in shift work adaptation—critical for shift worker health—can in part be explained by biological mechanisms for seasonal timing.

Background: Changes in the daily rhythm can trigger migraine attacks. The sensitivity for triggering attacks is closely linked to the regulation of biological rhythms controlled by the hypothalamus. In over 70 countries around the world, the time is changed between daylight savin…

Background: Changes in the daily rhythm can trigger migraine attacks. The sensitivity for triggering attacks is closely linked to the regulation of biological rhythms controlled by the hypothalamus. In over 70 countries around the world, the time is changed between daylight savings time and standard time twice a year due to legal regulations. The aim of this study was to investigate whether the time change has an influence on migraine. Methods: In this retrospective study, the headache frequency of patients with episodic or chronic migraine at a tertiary headache center in the years 2020, 2021, and 2022 was evaluated. The primary outcome measure was the frequency of migraine occurrence on either Sunday or Monday of the time change weekend compared to Sunday or Monday before or Sunday or Monday after the time change. Results: Data from 258 patients were analyzed (86.8% women; average age: 51.5 years; average headache frequency: 7.7 days/month; 83.3% episodic migraine). Our results showed a significant increase of 6.4% in migraine frequency on the Sunday and/or Monday in the week after the time change in spring compared to the week before the change. In autumn, conversely, there was a significant reduction of 5.5% in migraine frequency on the Sunday and/or Monday one week after the time change compared to the week before the change. The factor responsible for the significant changes was the increase in migraines on Monday one week after the time change in spring and the decrease in migraines on Sunday one week after the time change in autumn. Conclusions: When switching from standard time to daylight savings time in the spring, the frequency of migraines increases significantly one week after the time change. In autumn, in comparison, there is an inverse trend with a reduction in migraine frequency. These data suggest that synchronization is disturbed when switching to daylight savings time. Conversely, synchronization normalizes in autumn. In view of the high prevalence of migraines, this can have extensive individual and social consequences.

The potential adoption of permanent Daylight Saving Time in the United States has reinvigorated research examining the impact of circadian misalignment on well-being. We conduct the first study that examines the effect of chronic circadian misalignment on mental health in the Uni…

The potential adoption of permanent Daylight Saving Time in the United States has reinvigorated
research examining the impact of circadian misalignment on well-being. We conduct the first study
that examines the effect of chronic circadian misalignment on mental health in the United States.
Our study utilizes plausibly exogenous variations in circadian misalignment, which persist as long
as time zones are used to standardize local time. In fact, this misalignment is worsened by the
current time-zone borders that uniformly shift westward from the optimal designs. Using the latest
causal machine learning technique, we overcome the limitations of conventional methods (such as
ordinary least squares and regression discontinuity) that arise in our empirical setting and obtain
robust findings of adverse mental health impacts, likely driven by sleep deprivation. Our results
also emphasize the potential benefit of adopting flexible work schedules in mitigating the health
risks associated with circadian misalignment.
KEYWORDS: mental health, sleep, circadian misalignment, time zones, causal machine learning

Summary We explored the effects of daylight saving time clock changes on sleep duration in a large accelerometer dataset. Our sample included UK Biobank participants (n = 11,780; aged 43–78 years) with accelerometer data for one or more days during th…

Summary

We explored the effects of daylight saving time clock changes on sleep duration in a large accelerometer dataset. Our sample included UK Biobank participants (n = 11,780; aged 43–78 years) with accelerometer data for one or more days during the 2 weeks surrounding the Spring and Autumn daylight saving time transitions from October 2013 and November 2015. Between‐individual t‐tests compared sleep duration on the Sunday (midnight to midnight) of the clock changes with the Sunday before and the Sunday after. We also compared sleep duration on all other days (Monday–Saturday) before and after the clock changes. In Spring, mean sleep duration was 65 min lower on the Sunday of the clock changes than the Sunday before (95% confidence interval −72 to −58 min), and 61 min lower than the Sunday after (95% confidence interval −69 to −53). In Autumn, the mean sleep duration on the Sunday of the clock changes was 33 min higher than the Sunday before (95% confidence interval 27–39 min), and 38 min higher than the Sunday after (95% confidence interval 32–43 min). There was some evidence of catch‐up sleep after both transitions, with sleep duration a little higher on the Monday–Friday than before, although this was less pronounced in Autumn. Future research should use large datasets with longer periods of accelerometer wear to capture sleep duration before and after the transition in the same individuals, and examine other aspects of sleep such as circadian misalignment, sleep fragmentation or daytime napping.