  Background: The corona virus disease 2019 (COVID-19) pandemic, which is
caused by severe acute respiratory syndrome coronavirus 2, is still localized
outbreak and has resulted in a high rate of infection and severe disease in
older patients with comorbidities. The vitamin D status of the population has
been found to be an important factor that could influence outcome of COVID-19.
However, whether vitamin D can lessen the symptoms or severity of COVID-19
still remains controversial. Methods: A total of 719 patients with confirmed
COVID-19 were enrolled retrospectively in this study from April 13 to June 6,
2022 at Shanghai Forth People's Hospital. The circulating levels of 25(OH)D3,
inflammatory factors, and clinical parameters were assayed. Time to viral RNA
clearance (TVRC), classification and prognosis of COVID-19 were used to
evaluate the severity of COVID-19 infection. Results: The median age was 76
years (interquartile range, IQR, 64.5-84.6), 44.1% of patients were male, and
the TVRC was 11 days (IQR, 7-16) in this population. The median level of
25(OH)D3 was 27.15 (IQR, 19.31-38.89) nmol/L. Patients with lower serum
25(OH)D3 had prolonged time to viral clearance, more obvious inflammatory
response, more severe respiratory symptoms and higher risks of impaired hepatic
and renal function. Multiple regression analyses revealed that serum 25(OH)D3
level was negatively associated with TVRC independently. ROC curve showed the
serum vitamin D level could predict the severity classification and prognosis
of COVID-19 significantly.Conclusions: Serum 25(OH)D3 level is independently
associated with the severity of COVID-19 in elderly, and it could be used as a
predictor of the severity of COVID-19. In addition, supplementation with
vitamin D might provide beneficial effects in old patients with COVID-19.
