Sleep quality worsened in an evening chronotype compared to others: a year-long longitudinal cohort study with prolonged lockdowns and restriction relaxations in RECETOX MU university employees

Background In 2020, people around the world were challenged by the outbreak of the COVID-19 pandemic. Countries responded with various restrictions, including lockdowns and stay-at-home orders, in an attempt to prevent the spread of the disease. Citizens were thus subjected to unprecedented uncertainty and stress. Prolonged exposure to such conditions may impact human health and well-being. One of the core aspects of proper physiological functioning is sleep. This prospective longitudinal study aims to investigate sleep quality and its relationship to chronotype over a year-long period from September 2020. Methods and findings Our year-long longitudinal prospective study focused on an employee cohort (N=54) at the Research Centre for Toxic Compounds in the Environment (RECETOX) of Masaryk University in the Czech Republic. During the first half of this period, three lockdowns with a cumulative duration of 100 days were imposed. During the second half of this period, the imposed restrictions were relaxed. Individuals were measured quarterly, i.e. at five time points. Sleep quality was measured using the Pittsburgh Sleep Quality Index (PSQI) while chronotype was established using the Reduced Morningness-Eveningness Questionnaire (rMEQ). We also used Perceived Stress Scale (PSS-14), Beck Depression Inventory (BDI-II), and General Anxiety Disorder-7 (GAD-7) to address potential confounders. The response rates of valid measurements across time points ranged from 87.04 % to 61.11 %. Our results show that sleep quality significantly worsened across the year for the evening chronotype but improved for the neutral and early chronotypes. Overall, over the year the incidence of poor sleep decreased by 16.13 % with 95% CI [-6.10%; 37.16%]. We did not find any significant sex differences in sleep quality. Perceived stress, symptoms of anxiety and depression were positively significantly associated with sleep problems in all measurements except in June. This study is limited by the small sample, decreasing number of individuals in chronotype categories and the lack of information on napping behavior. Conclusion These findings shed new light on the long-term influence of pandemic-related restrictions on individuals and particularly on the potentially more vulnerable evening chronotypes. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was financialy supported by OP RDE project CETOCOEN Plus No. CZ.02.1.01/0.0/0.0/15\_003/0000469. Authors thanks the RECETOX Research Infrastructure (No LM2018121) financed by the Ministry of Education, Youth and Sports, and the Operational Programme Research, Development and Education (the CETOCOEN EXCELLENCE project No. CZ.02.1.01/0.0/0.0/17\_043/0009632) for supportive background, and the European Union’s Horizon 2020 research and innovation program under grant agreement No 857560. This publication reflects only the author's view, and the European Commission is not responsible for any use that may be made of the information it contains. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study was approved by the Masaryk University (MU) Ethics Committee. The cohort consists of volunteers from the employees of the Research Center for Toxic Compounds in the Environment (RECETOX) at MU. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes o Because the study involves human research participants from a relatively small and closed group of participants, and includes their personal and sensitive data, we decided to provide the data set in anonymized form upon request. Requests for data can be sent to ekv{at}muni.cz. The data underlying the results presented in the study are available in the Supplementary Material.