Impaired Vitamin D Metabolism in Hospitalized COVID-19 Patients

There is increasing data regarding the association between vitamin D and COVID-19. This study aimed to reveal the alterations of vitamin D metabolism in the setting of COVID-19. We examined 119 adult COVID-19 inpatients and 44 apparently healthy adult individuals with similar serum 25OH-D(3) levels as a reference group. The assessment included serum biochemical parameters (total calcium, albumin, phosphorus, creatinine), parathyroid hormone (PTH), vitamin D-binding protein (DBP), vitamin D metabolites (25OH-D(3), 25OH-D(2), 1,25(OH)(2)D(3), 3-epi-25OH-D(3), 24,25(OH)(2)D(3) and D(3)) and free 25OH-D. COVID-19 patients had in general very low vitamin D levels (median 25OH-D(3) equals 10.8 ng/mL), accompanied by an increased production of the active vitamin D metabolite (1,25(OH)(2)D(3)), estimated as higher 1,25(OH)(2)D(3) serum levels (61 [44; 81] vs. 40 [35; 50] pg/mL, p < 0.001) and lower 25OH-D(3)/1,25(OH)(2)D(3) ratio (175 [112; 260] vs. 272 [200; 433], p < 0.001) which is presumably aimed at preventing hypocalcemia. Patients with COVID-19 also had elevated DBP (450 [386; 515] vs. 392 [311; 433] mg/L, p < 0.001) and low free 25OH-D levels (<LoB vs. 3.9 [3.2; 4.4] pg/mL, p < 0.001). Follow-up assessment of the COVID-19 inpatients showed recovery of the observed changes. Overall, hospitalized patients with an acute course of COVID-19 have not only very low levels of 25OH-D but also profound abnormalities in the metabolism of vitamin D regardless of the clinical course of the disease. These alterations might exacerbate existing vitamin D deficiency and its negative impact.