Low 1,25-dihydroxyvitamin D levels are associated with severe COVID-19: an observational study in hospitalized patients

Background This study aimed to evaluate the association of serum 25-hydroxyvitamin D (25(OH)D) and 1,25-dihydroxyvitamin D (1,25(OH) 2 D) levels with clinical severity and mortality among hospitalized patients with moderate and severe COVID-19. Methods A total of 185 adult patients (≥18 years) with confirmed SARS-CoV-2 PCR positivity and without chronic kidney disease, admitted between March and May 2020, were included. Clinical characteristics, laboratory parameters, and serum 25(OH)D and 1,25(OH) 2 D levels were assessed. Factors associated with severe disease and mortality were determined using multivariate logistic regression and Cox regression analyses. Results Of the patients, 114 had moderate disease and 71 had severe disease. Length of hospital stay, intensive care unit (ICU) admission, and mortality rates were significantly higher in the severe group. While 25(OH)D levels were lower in the moderate group, 1,25(OH) 2 D levels were markedly reduced in severe cases. Multivariate analysis identified prolonged hospital stay, ICU admission history, and low 1,25(OH) 2 D levels were independently associated with severe disease. Independently associated factors with mortality were ICU admission ( p < 0.001), high troponin levels ( p = 0.003) and prolonged activated partial thromboplastin time (APTT) ( p = 0.04). Although vitamin D deficiency was associated with severe disease, it was not independently associated with mortality. Conclusion Reduced 1,25(OH) 2 D levels are associated with severe COVID-19 and may serve as a meaningful biomarker for predicting disease severity. These findings suggest that assessing 1,25(OH) 2 D levels may support clinical decision-making, particularly in patients at risk for severe COVID-19 or ARDS.