{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,21]],"date-time":"2026-07-21T15:19:19Z","timestamp":1784647159979,"version":"3.55.0"},"reference-count":31,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2025,6,18]],"date-time":"2025-06-18T00:00:00Z","timestamp":1750204800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Nutr."],"abstract":"<jats:sec><jats:title>Background<\/jats:title><jats:p>Vitamin D deficiency (VDD) has been associated with adverse outcomes in COVID-19 patients during the early pandemic phases, but whether this association persists in the post-Omicron era remains uncertain. This study aimed to investigate the evolving relationship between VDD and COVID-19 outcomes across pandemic phases using a large healthcare database.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>We conducted a retrospective cohort study using the TriNetX Analytics Network, analyzing propensity-matched cohorts comprising 24,236 pairs from the post-Omicron phase (June 2022\u2013December 2023) and 22,638 pairs from the pre-Omicron phase (January 2020\u2013December 2021). VDD was defined as a serum 25-hydroxyvitamin D level &amp;lt; 20 ng\/ml, with vitamin D-sufficient patients (\u226530 ng\/ml) serving as controls. The primary outcome was 30-day all-cause mortality, with secondary outcomes including acute kidney injury, respiratory failure, pneumonia, sepsis, and ICU admission.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>The 30-day mortality in VDD vs. vitamin D-sufficient patients decreased from 1.43% vs. 0.39% [odds ratio (OR), 3.67; 95% CI, 2.90\u20134.64; <jats:italic>p<\/jats:italic> &amp;lt; 0.001] in the pre-Omicron phase to 0.89% vs. 0.49% (OR, 1.82; 95% CI, 1.46\u20132.28; <jats:italic>p<\/jats:italic> &amp;lt; 0.001) in the post-Omicron phase. Similar risk attenuation was observed across all secondary outcomes, including acute kidney injury (OR, 2.11; 95% CI, 1.92\u20132.31 vs. OR, 1.41; 95% CI, 1.29\u20131.54; both <jats:italic>p<\/jats:italic> &amp;lt; 0.001), respiratory failure (OR, 1.66; 95% CI, 1.44\u20131.92 vs. OR, 1.34; 95% CI, 1.16\u20131.54; both <jats:italic>p<\/jats:italic> &amp;lt; 0.001), and pneumonia (OR, 1.34; 95% CI, 1.16\u20131.55 vs. OR, 1.23; 95% CI, 1.07\u20131.42; <jats:italic>p<\/jats:italic> &amp;lt; 0.001 and <jats:italic>p<\/jats:italic> = 0.004, respectively). Risk factor analysis identified several significant mortality predictors among patients with VDD in the post-Omicron phase, including malnutrition (OR, 4.34; 95% CI, 3.18\u20135.92; <jats:italic>p<\/jats:italic> &amp;lt; 0.001), liver disease (OR, 3.08; 95% CI, 2.23\u20134.25; <jats:italic>p<\/jats:italic> &amp;lt; 0.001), and neoplasms (OR, 2.63; 95% CI, 2.01\u20133.45; <jats:italic>p<\/jats:italic> &amp;lt; 0.001).<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusion<\/jats:title><jats:p>VDD continues to be associated with adverse COVID-19 outcomes in the post-Omicron phase, albeit with a reduced magnitude. These findings support the importance of vitamin D screening in high-risk COVID-19 patients, while emphasizing the need for adaptive risk assessment strategies that incorporate both established and emerging risk factors in the current pandemic landscape.<\/jats:p><\/jats:sec>","DOI":"10.3389\/fnut.2025.1583276","type":"journal-article","created":{"date-parts":[[2025,6,18]],"date-time":"2025-06-18T09:01:24Z","timestamp":1750237284000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":9,"title":["Association between vitamin D deficiency and clinical outcome in patients with COVID-19 in the post-Omicron 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