{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,9]],"date-time":"2026-07-09T04:01:41Z","timestamp":1783569701958,"version":"3.55.0"},"reference-count":41,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2021,4,13]],"date-time":"2021-04-13T00:00:00Z","timestamp":1618272000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100005847","name":"Health and Medical Research Fund","doi-asserted-by":"publisher","award":["Vit D-HKU"],"award-info":[{"award-number":["Vit D-HKU"]}],"id":[{"id":"10.13039\/501100005847","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nutrients"],"abstract":"<jats:p>Background: During the coronavirus disease 2019 (COVID-19) pandemic, the implementation of social distancing and home confinement measures may elevate the risk of vitamin D deficiency particularly for infants. This study aimed to quantify changes in vitamin D level among infants and toddlers in Hong Kong after the COVID-19 outbreak. Methods: We recruited 303 infants and toddlers aged 2\u201324 months by stratified random sampling from 1 June 2019 to November 30, 2020. Regression models were used to estimate the effect of time on infants\u2019 serum 25-hydroxyvitamin D (25(OH)D) level overall and by age groups before and after the outbreak. Interrupted time series (ITS) analysis was performed to examine the sustained effect of COVID-19 on their serum 25(OH)D level. Results: The ITS results showed no immediate reduction in serum 25(OH)D level among infants, but a decreasing trend was observed in the subsequent months post-outbreak at a monthly decline rate of \u22126.32 nmol\/L. When analyzed by age group, the magnitude of post-outbreak reduction in 25(OH)D was stronger among younger infants (aged 2\u20136 months). Conclusion: Guidelines and recommendations should be given to pregnant women and mothers to ensure sufficient vitamin D level in their infants during the COVID-19 period.<\/jats:p>","DOI":"10.3390\/nu13041270","type":"journal-article","created":{"date-parts":[[2021,4,13]],"date-time":"2021-04-13T05:31:37Z","timestamp":1618291897000},"page":"1270","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":18,"title":["Impact of COVID-19 Pandemic on Serum Vitamin D Level among Infants and Toddlers: An Interrupted Time Series Analysis and before-and-after Comparison"],"prefix":"10.3390","volume":"13","author":[{"given":"Rosa S.","family":"Wong","sequence":"first","affiliation":[{"name":"Department of Paediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6647-4346","authenticated-orcid":false,"given":"Keith T. S.","family":"Tung","sequence":"additional","affiliation":[{"name":"Department of Paediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6188-7587","authenticated-orcid":false,"given":"Hung-Kwan","family":"So","sequence":"additional","affiliation":[{"name":"Department of Paediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wilfred H. S.","family":"Wong","sequence":"additional","affiliation":[{"name":"Department of Paediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5785-6772","authenticated-orcid":false,"given":"Siew Yan","family":"Wong","sequence":"additional","affiliation":[{"name":"Department of Paediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6066-5333","authenticated-orcid":false,"given":"Hing Wai","family":"Tsang","sequence":"additional","affiliation":[{"name":"Department of Paediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7897-716X","authenticated-orcid":false,"given":"Joanna Y. L.","family":"Tung","sequence":"additional","affiliation":[{"name":"Department of Paediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong, China"},{"name":"Department of Paediatrics, Hong Kong Children\u2019s Hospital, Hong Kong, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0333-0059","authenticated-orcid":false,"given":"Gilbert T.","family":"Chua","sequence":"additional","affiliation":[{"name":"Department of Paediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1802-2120","authenticated-orcid":false,"given":"Marco H. K.","family":"Ho","sequence":"additional","affiliation":[{"name":"Department of Paediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ian C. K.","family":"Wong","sequence":"additional","affiliation":[{"name":"Centre for Safe Medication Practice and Research, Department of Pharmacology and Pharmacy, The University of Hong Kong, Hong Kong, China"},{"name":"Research Department of Practice and Policy, UCL School of Pharmacy, London WC1E 6BT, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Patrick","family":"Ip","sequence":"additional","affiliation":[{"name":"Department of Paediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,4,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"E15","DOI":"10.1148\/radiol.2020200490","article-title":"Coronavirus disease 2019 (COVID-19): A perspective from China","volume":"296","author":"Zu","year":"2020","journal-title":"Radiology"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"e55","DOI":"10.1056\/NEJMp2005118","article-title":"Novel coronavirus and old lessons\u2014Preparing the health system for the pandemic","volume":"382","author":"Hick","year":"2020","journal-title":"N. 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