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. 2021 Jul 13;11:14413. doi: 10.1038/s41598-021-93924-z

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© The Author(s) 2021

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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Sleep patterns and resting heart rate measures by country. (a) midsleep time, (b) midsleep variability and (c) resting heart rate from Jan to Jul 2020 (orange curves), compared to Jan–Dec 2019 (purple curves). Dates in 2019 were shifted in order to ensure a matching by day of the week. Daylight savings time (social clocks shifted later by 1 h) began in March in select countries of the Northern Hemisphere, and ended in April in Australia and New Zealand (social clocks shifted earlier by 1 h), explaining sudden shifts in midsleep time and variability on these dates.