Vitamin D levels in SARS-CoV-2: Do current adequacy thresholds reflect clinical risk? Insights from a large Turkish cohort.

The clinical relevance of serum 25-hydroxyvitamin D [25(OH)D] concentrations in SARS-CoV-2 infection remains uncertain. Most thresholds used to define adequacy were developed for skeletal outcomes, and it is unclear whether they reflect immunerelated risk. To examine whether serum 25(OH)D levels are associated with disease severity, inflammatory and biochemical markers, or clinical outcomes, we conducted a retrospective cohort analysis including 1136 hospitalized patients with PCR-confirmed SARS-CoV-2 infection. Clinical severity at admission, oxygen requirement, intensive care unit transfer, invasive ventilation, inflammatory markers, length of hospital stay, and in-hospital mortality were compared across vitamin D groups. No significant associations were observed between serum 25(OH)D levels and clinical or laboratory findings. Correlation analyses likewise did not reveal meaningful relationships with inflammatory parameters. In this large hospitalized cohort with predominantly low serum 25(OH)D concentrations, we found no evidence that vitamin D status influenced COVID-19 severity or outcomes. These results indicate that commonly applied adequacy thresholds, including lower immune-related levels, may not provide useful risk stratification in hospitalized patients with COVID-19.