Case-control study of serum vitamin D concentrations in hospitalised patients with COVID-19 and hospitalised controls suffering with respiratory tract infections of differing aetiology.

This study explored the prevalence of low serum vitamin D in patients admitted with acute respiratory tract infections (ARTIs) such as COVID-19. This study investigated whether patients with COVID-19 had lower serum vitamin D compared with patients with ARTIs of other aetiology. A case-control study was performed with cases of COVID-19 and controls of non-COVID-19 ARTIs. Patients were enrolled from a single general medical ward in a secondary care hospital between 15 April 2020 and 15 May 2020. Exclusion criteria were an oxygen requirement of >8 L/min. Data collected included serum 25-hydroxyvitamin D concentration, venous plasma glucose concentration and heamoglobin A1c. Outcomes measured were length of hospital stay, deaths, the need for high dependency and intensive care unit involvement. A total of 60 patients of five ethnic groups were enrolled, 85% (n=46) were of White-British ethnicity. The data analysis is based on these 46 patients of which 24 were non-COVID-19 patients with ARTI and 22 were patients with COVID-19. Overall, 80% of the study population had a serum vitamin D concentration below 50 nmol/L with median concentrations of 30 nmol/L and 35 nmol/L for patients with COVID-19 and non-COVID-19 ARTIs respectively. A Mann-Whitney sign-ranked test with respect to serum vitamin D concentration found no statistically significant difference between cases and controls, p=0.09. There was no significant difference in the length of stay, body mass index and rates of various comorbidities such as diabetes mellitus (DM), hypertension and lung disease in both study groups. However, DM was found to be associated with lower serum vitamin D concentrations. The results of this study support published literature showing an association between low serum vitamin D and ARTIs including COVID-19. However, this study did not identify patients with COVID-19 to have a statistically significant lower serum vitamin D concentration than non-COVID-19 patients with ARTI.