The recent COVID-19 pandemic has created significant health challenges, necessitating the enhancement of our immune systems. Through the modulation of immune response, Vitamin D vitally reduces the risk of infection and minimizes mortality rates. This retrospective study aimed to assess the relationship between the severity of COVID-19 infection in diabetes individuals and their blood vitamin D levels. A total of 2070 COVID-19 patients were split into two groups for this case-control retrospective study: non-diabetic (n=1723) and diabetic (n= 347). Electronic medical records from March to August 2020 obtained from the King Faisal Specialist Hospital and Research Center and Al-Noor Specialist Hospital, Saudi Arabia, were used as the base of the extraction of Demographic and clinical laboratory data. COVID-19 infection was confirmed in all patients through RT-PCR. Serum vitamin D level was measured by automated ELISA. A significant difference (p<0.05) in blood vitamin D levels between COVID-19 individuals with diabetes and those without was noted from the results of the study. We observed a marginal but significant negative correspondence between vitamin D levels and oxygen saturation as a measure of COVID-19 severity (p=0.016). Vitamin D levels were also found to be positively correlated with inflammatory markers such as C-reactive protein and erythrocyte sedimentation rate (p=0.038 and p<0.001,) while showing a negative correlation with D-dimer (p=0.017). The results of our investigation suggest that vitamin D supplementation may be helpful in the management and prevention of COVID-19 infection, as well as in reducing the severity of risk and inflammation among diabetic patients.