{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T02:00:58Z","timestamp":1760148058142,"version":"build-2065373602"},"reference-count":27,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2023,3,24]],"date-time":"2023-03-24T00:00:00Z","timestamp":1679616000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Medical University of Lodz","award":["503\/1-107-03\/503-11-001-19-00"],"award-info":[{"award-number":["503\/1-107-03\/503-11-001-19-00"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nutrients"],"abstract":"<jats:p>Background: It has been speculated that higher concentrations of 25-hydroxy-vitamin D (25OHD) provide some protection against COVID-19. We assessed whether there is any relationship between 25OHD concentrations and the subsequent development of COVID-19 infection. Materials and Methods: Concentrations of 25OHD were measured in March\u2013April 2020 in 134 healthy subjects (57 males), age range 6\u201350, from a single urban general practice in central Poland. Data on COVID-19 infection during the subsequent 12 months (prior to the vaccination program) were obtained from the national database of COVID-19 cases. None of the subjects received any 25OHD supplements. Results: The average 25OHD concentrations were 18.1 \u00b1 7.39 ng\/mL (37.3% had 25OHD above 20 ng\/mL). Thirty-one (23.1%) patients developed COVID-19 infection, but an increased risk was only observed in individuals with 25OHD concentrations below 12 ng\/mL (COVID-19 infection in 11 out of 25 patients (44%) with 25OHD &lt; 12 ng\/mL versus 20 out of 109 (18.3%) for those with 25OHD above 12 ng\/mL, p = 0.0063). Such a relationship was no longer observed for subjects with 25OHD concentrations above 20 ng\/mL (p = 0.2787). Conclusions: Although only a minority of healthy subjects had 25OHD concentrations above 20 ng\/mL in spring, an increased risk of subsequent COVID-19 infection was only observed in those with severe 25OHD deficiency (&lt;12 ng\/mL).<\/jats:p>","DOI":"10.3390\/nu15071581","type":"journal-article","created":{"date-parts":[[2023,3,24]],"date-time":"2023-03-24T08:43:03Z","timestamp":1679647383000},"page":"1581","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Frequency of COVID-19 Infection as a Function of Vitamin D Levels"],"prefix":"10.3390","volume":"15","author":[{"given":"Magdalena","family":"Basi\u0144ska-Lewandowska","sequence":"first","affiliation":[{"name":"\u201cYour Family Doctor\u201d, General Practice Surgery, 93-324 Lodz, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9113-2804","authenticated-orcid":false,"given":"Krzysztof","family":"Lewandowski","sequence":"additional","affiliation":[{"name":"Department of Endocrinology and Metabolic Diseases, Medical University of Lodz, 90-419 Lodz, Poland"},{"name":"Department of Endocrinology and Metabolic Diseases, Polish Mother\u2019s Memorial Hospital\u2014Research Institute, 93-338 Lodz, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3690-5368","authenticated-orcid":false,"given":"Wojciech","family":"Horzelski","sequence":"additional","affiliation":[{"name":"Department of Mathematics and Computer Science, University of Lodz, 90-238 Lodz, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8748-3337","authenticated-orcid":false,"given":"Andrzej","family":"Lewi\u0144ski","sequence":"additional","affiliation":[{"name":"Department of Endocrinology and Metabolic Diseases, Medical University of Lodz, 90-419 Lodz, Poland"},{"name":"Department of Endocrinology and Metabolic Diseases, Polish Mother\u2019s Memorial Hospital\u2014Research Institute, 93-338 Lodz, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0019-4269","authenticated-orcid":false,"given":"El\u017cbieta","family":"Skowro\u0144ska-J\u00f3\u017awiak","sequence":"additional","affiliation":[{"name":"Department of Endocrinology and Metabolic Diseases, Medical University of Lodz, 90-419 Lodz, Poland"},{"name":"Department of Endocrinology and Metabolic Diseases, Polish Mother\u2019s Memorial Hospital\u2014Research Institute, 93-338 Lodz, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2023,3,24]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Sassi, F., Tamone, C., and D\u2019Amelio, P. 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