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      Daylight Saving Time and Artificial Time Zones – A Battle Between Biological and Social Times

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          Abstract

          Many regions and countries are reconsidering their use of Daylight Saving Time (DST) but their approaches differ. Some, like Japan, that have not used DST over the past decades are thinking about introducing this twice-a-year change in clock time, while others want to abolish the switch between DST and Standard Time, but don’t agree which to use: California has proposed keeping perennial DST (i.e., all year round), and the EU debates between perennial Standard Time and perennial DST. Related to the discussion about DST is the discussion to which time zone a country, state or region should belong: the state of Massachusetts in the United States is considering switching to Atlantic Standard Time, i.e., moving the timing of its social clock (local time) 1 h further east (which is equivalent to perennial DST), and Spain is considering leaving the Central European Time to join Greenwich Mean Time (GMT), i.e., moving its social timing 1 h further west. A wave of DST discussions seems to periodically sweep across the world. Although DST has always been a political issue, we need to discuss the biology associated with these decisions because the circadian clock plays a crucial role in how the outcome of these discussions potentially impacts our health and performance. Here, we give the necessary background to understand how the circadian clock, the social clock, the sun clock, time zones, and DST interact. We address numerous fallacies that are propagated by lay people, politicians, and scientists, and we make suggestions of how problems associated with DST and time-zones can be solved based on circadian biology.

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          Most cited references46

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          Evening exposure to a light-emitting diodes (LED)-backlit computer screen affects circadian physiology and cognitive performance.

          Many people spend an increasing amount of time in front of computer screens equipped with light-emitting diodes (LED) with a short wavelength (blue range). Thus we investigated the repercussions on melatonin (a marker of the circadian clock), alertness, and cognitive performance levels in 13 young male volunteers under controlled laboratory conditions in a balanced crossover design. A 5-h evening exposure to a white LED-backlit screen with more than twice as much 464 nm light emission {irradiance of 0,241 Watt/(steradian × m(2)) [W/(sr × m(2))], 2.1 × 10(13) photons/(cm(2) × s), in the wavelength range of 454 and 474 nm} than a white non-LED-backlit screen [irradiance of 0,099 W/(sr × m(2)), 0.7 × 10(13) photons/(cm(2) × s), in the wavelength range of 454 and 474 nm] elicited a significant suppression of the evening rise in endogenous melatonin and subjective as well as objective sleepiness, as indexed by a reduced incidence of slow eye movements and EEG low-frequency activity (1-7 Hz) in frontal brain regions. Concomitantly, sustained attention, as determined by the GO/NOGO task; working memory/attention, as assessed by "explicit timing"; and declarative memory performance in a word-learning paradigm were significantly enhanced in the LED-backlit screen compared with the non-LED condition. Screen quality and visual comfort were rated the same in both screen conditions, whereas the non-LED screen tended to be considered brighter. Our data indicate that the spectral profile of light emitted by computer screens impacts on circadian physiology, alertness, and cognitive performance levels. The challenge will be to design a computer screen with a spectral profile that can be individually programmed to add timed, essential light information to the circadian system in humans.
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            Health disorders of shift workers.

            The effects of shift work on physiological function through disruption of circadian rhythms are well described. However, shift work can also be associated with specific pathological disorders. This article reviews the evidence for a relationship between specific medical disorders and working at night or on shift systems. The strongest evidence exists for an association with peptic ulcer disease, coronary heart disease and compromised pregnancy outcome.
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              Chronotype Is Independently Associated With Glycemic Control in Type 2 Diabetes

              OBJECTIVE To examine whether chronotype and daily caloric distribution are associated with glycemic control in patients with type 2 diabetes independently of sleep disturbances. RESEARCH DESIGN AND METHODS Patients with type 2 diabetes had a structured interview and completed questionnaires to collect information on diabetes history and habitual sleep duration, quality, and timing. Shift workers were excluded. A recently validated construct derived from mid-sleep time on weekends was used as an indicator of chronotype. One-day food recall was used to compute the temporal distribution of caloric intake. Hierarchical linear regression analyses controlling for demographic and sleep variables were computed to determine whether chronotype was associated with HbA1c values and whether this association was mediated by a higher proportion of caloric intake at dinner. RESULTS We analyzed 194 completed questionnaires. Multiple regression analyses adjusting for age, sex, race, BMI, insulin use, depressed mood, diabetes complications, and perceived sleep debt found that chronotype was significantly associated with glycemic control (P = 0.001). This association was partially mediated by a greater percentage of total daily calories consumed at dinner. CONCLUSIONS Later chronotype and larger dinner were associated with poorer glycemic control in patients with type 2 diabetes independently of sleep disturbances. These results suggest that chronotype may be predictive of disease outcomes and lend further support to the role of the circadian system in metabolic regulation.
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                Author and article information

                Contributors
                Journal
                Front Physiol
                Front Physiol
                Front. Physiol.
                Frontiers in Physiology
                Frontiers Media S.A.
                1664-042X
                07 August 2019
                2019
                : 10
                : 944
                Affiliations
                [1] 1Institute of Medical Psychology, Ludwig Maximilian University of Munich , Munich, Germany
                [2] 2Division of Sleep and Circadian Disorders, Brigham and Women’s Hospital, Harvard Medical School , Boston, MA, United States
                Author notes

                Edited by: Sara Montagnese, University of Padova, Italy

                Reviewed by: Alireza Mani, University College London, United Kingdom; Horacio De La Iglesia, University of Washington Tacoma, United States

                *Correspondence: Till Roenneberg, roenneberg@ 123456lmu.de

                This article was submitted to Chronobiology, a section of the journal Frontiers in Physiology

                Article
                10.3389/fphys.2019.00944
                6692659
                31447685
                76497ed8-e907-4675-9a59-351dcd6cba1e
                Copyright © 2019 Roenneberg, Winnebeck and Klerman.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                History
                : 07 May 2019
                : 09 July 2019
                Page count
                Figures: 4, Tables: 1, Equations: 0, References: 88, Pages: 12, Words: 0
                Funding
                Funded by: NIH Office of the Director 10.13039/100000052
                Award ID: R01-HL128538
                Award ID: P01-AG009975
                Award ID: K24-HL105664
                Categories
                Physiology
                Review

                Anatomy & Physiology
                circadian,social jetlag,circadian misalignment,time zones,entrainment (light)
                Anatomy & Physiology
                circadian, social jetlag, circadian misalignment, time zones, entrainment (light)

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