BackgroundCoronavirus disease 2019 (COVID-19) is a pandemic disease. Experiments with influenza and severe acute respiratory syndrome (SARS) have shown supplemental vitamin D can reduce the risk of infection and death.AimThis study was performed to evaluate the relationship between vitamin D levels and the severity and outcome of admitted patients with COVID-19.Material and MethodsThis cross-sectional study was performed on COVID-19 cases diagnosed by examining RT-PCR assay for SARS-CoV-2 or a set of symptoms and typical findings in lung CT scan. Based on clinical and radiologic characteristics, the patients were categorized as mild, moderate, severe, and critical. Calcium, phosphorus, albumin, creatinine, and serum 25 hydroxy vitamin D were measured and their correlation with the severity and outcome were analyzed.ResultsFrom May 1 to June 31, 2020, 508 patients ((442 patients in general wards and 66 patients in intensive care unit (ICU)) were included in this study. The participants were 56±17 years old (mean ±SD) (range from 14 to 95 years) and 52% were male. According to the past medical history, 190 (37.4%) of them had comorbidity. Concerning severity, 13.2%, 42.3%, 35.4%, and 9.1% had the mild, moderate, severe, and critical disease, respectively. The in-hospital mortality rate was 10.8%. In the multivariate regression analysis, age had a positive correlation and use of vitamin D supplement, serum level of 25 OH vitamin D, calcium, and albumin had a negative correlation with disease severity and admission to ICU. Poor outcome was inversely related to serum levels of vitamin D, calcium, albumin, and renal function. Vitamin D deficiency increased the rate of ICU admission by 2.7 times (95%CI=1.288-5.91, P=0.009).ConclusionIn patients who are hospitalized due to COVID-19, low 25-hydroxyvitamin D, hypocalcemia, and hypoalbuminemia are associated with severe disease, ICU admission, and an increase in mortality.