20.500.12556/DiRROS-29216 Ten-year trends in serum 25-hydroxyvitamin D in Slovenia (2014–2023) laboratory-based data from tested individuals and COVID-19-period changes Background: Vitamin D status is influenced by season, age, and public health messaging. The COVID-19 pandemic was accompanied by heightened interest in vitamin D, but long-term national data from Central/Eastern Europe remain limited. We aimed to characterize 10-year trends, seasonal variation, and demographic determinants of serum 25-hydroxyvitamin D [25(OH)D] in Slovenia, with particular focus on changes during the COVID-19 period. Methods: We performed a retrospective cross-sectional analysis of all serum 25(OH)D measurements performed at the Slovenian national reference laboratory between January 2014 and December 2023. The core analytic cohort included 106,875 patients with valid 25(OH)D results, aged 0–100 years. Vitamin D status was classified as deficient (<30 nmol/L), insufficient (30–50 nmol/L), adequate (50–75 nmol/L), and optimal (>75 nmol/L). Temporal trends, seasonal patterns, and age- and sex-specific differences were assessed using non-parametric tests and Kendall’s τ. Results: Mean 25(OH)D concentration over the study period was 61.9 ± 34.2 nmol/L; 16.0% of patients were deficient and 22.8% insufficient. Annual mean 25(OH)D increased from 57.0 nmol/L in 2014 to 67.2 nmol/L in 2023, with a significant upward temporal trend and a 14.6% higher mean level during 2020–2023 compared with 2014–2019. Seasonal variation was pronounced (≈20% higher summer–autumn vs. winter–spring), and vitamin D status declined progressively with age, with the highest deficiency prevalence in patients ≥ 70 years. Females had slightly higher 25(OH)D than males, although absolute differences were small. Conclusions: This laboratory-based analysis of tested patients showed higher 25(OH)D concentrations during and after the COVID-19 period, superimposed on persistent seasonal and age-related gradients. These observations identify older adults and winter testing periods as important contexts for vitamin D optimization, but they should be interpreted as descriptive trends among tested individuals rather than as evidence of causal pandemic effects or population-wide prevalence changes. 25-hydroxyvitamin D seasonal variation deficiency age factors COVID-19 pandemic 25-hidroksivitamin D sezonske spremembe pomanjkanje starostni dejavniki pandemija COVID-19 true false true Angleški jezik Slovenski jezik Neznano 2026-04-24 14:38:17 2026-04-24 14:38:18 2026-04-25 03:53:43 0000-00-00 00:00:00 2026 0 0 Nasl. z nasl. zaslona; Opis vira z dne 8. 4. 2026; str. 1-22 iss. 7, [article no.] 1168 Vol. 18 2026 0000-00-00 Zaloznikova Objavljeno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 616.98:578.834 2072-6643 10.3390/nu18071168 274444547 RAZ_Osredkar_Josko_2026.pdf RAZ_Osredkar_Josko_2026.pdf 1 E4445C2AE21D6B38413E6C5D2F06ED71 b6e0048212a5d729418a6d623294a2184896163f6f104188463476a027bca900 94c146ad-3fda-11f1-ad5f-001a4af901a5 https://dirros.openscience.si/Dokument.php?lang=slv&id=43699 https://www.mdpi.com/2072-6643/18/7/1168 1 7a1fef5a-3fda-11f1-ad5f-001a4af901a5 https://dirros.openscience.si/Dokument.php?lang=slv&id=43698 Univerzitetni klinični center Ljubljana 0 0 0