Contents lists available at ScienceDirect European Journal of Internal Medicine journal homepage: www.elsevier.com/locate/ejim Review Impact of Daylight Saving Time on circadian timing system: An expert statement Meira e Cruz M. a, ⁎ , Miyazawa M. i , Manfredini R. c , Cardinali D. d , Madrid J.A. e , Reiter R. f , Araujo J.F. g , Agostinho R. h , Acuña-Castroviejo D. b a Sleep Unit, Cardiovascular Center, University of Lisbon, Faculty of Medicine, Lisbon, Portugal b Department of Physiology, Faculty of Medicine, Center of Biomedical Research, Parque Tecnologico de Ciencias de la Salud, University of Granada, Granada, Spain c Department of Medical Sciences, Faculty of Medicine, Surgery and Prevention, University of Ferrara, Ferrara, Italy d BIOMED-UCA-CONICET, Department of Teaching and Research, Faculty of Medical Sciences, Pontificia Catholic University of Argentina, Buenos Aires, Argentina e Department of Physiology, Faculty of Biology, University of Murcia, Spain f Department of Cell Systems and Anatomy, UT Health, United States g Laboratory of Neurobiology and Biological Rhythmicity, Department of Physiology and Biophysics, Federal University of Rio Grande do Norte, Natal, Brazil h Institute of Astrophysic and Space Sciences, Department of Physics, Faculty of Sciences, University of Lisbon, Lisbon, Portugal i Department of Immunology, Faculty of Medicine and Anti-Aging Center, Kindai University, Osaka, Japan 1. Introduction Even though that in the very beginning of Daylight Saving Time (DST) policy, standards were decided individually by each country, and were not regulated, most European member States have progressively been adopting the so called “summer time” since 1970s or 1980s which had been gradually harmonized under EU law [1]. Public discomfort have been argued for years and claims from several social groups re- garding the need for a public inquiry were attended. However, after European Union decided to properly ask citizens about their feelings regarding Daylight Saving Time, a small fraction of European citizens (68% from Germany) had told that they don't want to change the time twice a year. Despite the very statistically biased result, there are still misgivings about the biomedical and clinical meanings of this position. Therefore a significant amount of uncertainty related to the actual impact of DST on health persists both in general public and in the clinical and scientific community. Actually, at the same time discussion seemed ready to be closed in EU, some countries persist with this trend and some others try to implement variants. 2. The group and the topics on discussion With this in mind, an international group of specialists in clinical medicine,physiologyandimmunologywithexpertiseonchronobiology and sleep medicine (Table 1) joined together in August 2018 with the aims of: 1) to reflect, analyze and clarify on the literature regarding the numerous effects potentially attributed to DST-induced circadian mis- alignment; 2) to define whether adherence to DST should be considered a dangerous rather risky behavior in terms of health and wellbeing. 3. World changed since DST was implemented Since Benjamin Franklin idea for saving coal with supplementary light in summer [2], world has developed and lamps, TVs, computers and smartphones became available for the majority of the population. Shiftwork and intercontinental travels are no longer rare conditions for a great number of people, and transitions between day and night be- came less marked by related geophysical factors like sun during day- timeanddarknessormoonlightduringnighttimetoconformtothelaw of social rules and “24 h open” commercial dictation. 4. DST - behind sleep It is still common that whenever talking about circadian rhythms, people think about sleep. There was 88 titles available in September 2018 on PubMed in answer to the search criteria of DST, most of them made reference to sleep/wake or to rest/activity cycle. That's actually the most obvious circadian rhythm and that is why it is used as the most common variable to study the impact of circadian disruption. Nevertheless, circadian timing system is a complex physio- logical network that comprises a hierarchy of peripheral oscillators (peripheral biological clocks) commanded by a central pacemaker, the suprachiasmatic nucleus (master clock). This well-organized and in- teractive system causes success to have the right time to occur in vir- tually all biological forms. Not only sleep and wake time, but also meal time, several hormones, blood pressure, the better time for alertness and attention, time for the greater immune protection, and time for beingwiseastheprefrontalcortex,sorelevantforcriticaljudgement,is influenced by circadian regulation. There are also times of risk to suffer disease that are regulated by https://doi.org/10.1016/j.ejim.2019.01.001 Received 29 October 2018; Received in revised form 2 January 2019; Accepted 3 January 2019 ⁎ Corresponding author. E-mail address: mcruz@medicina.ulisboa.pt (M. Meira e Cruz). European Journal of Internal Medicine 60 (2019) 1–3 Available online 05 January 2019 0953-6205/ © 2019 Published by Elsevier B.V. on behalf of European Federation of Internal Medicine. T