The role of vitamin D as a preventive strategy in COVID-19 infections: evidence from South Asia

Regional evidence on the role of vitamin D in the prevention of COVID-19 and its sequalae remains inconclusive and sparse. This study aimed to determine the association of COVID-19 status and severity with vitamin D among adults in Colombo District, Sri Lanka. A sex-matched case–control study was conducted among 104 RT-PCR-confirmed COVID-19 patients recruited from two major hospitals designated as COVID-19 treating centres and 104 RT-PCR negative adults recruited from the catchment area of the two hospitals. Non-fasting blood samples obtained from cases upon hospital admission and from controls upon release from 14-day quarantine period were analysed for serum 25(OH)D using chemiluminescence assay. Serum level < 50.0 nmol/L was identified as vitamin D deficiency (VDD). Cases were older while the controls had fewer persons with co-morbidities. Cases (median = 30.0; IQR = 21.2 nmol/L) had significantly lower 25(OH)D compared to controls (median = 35.9; IQR = 28.3 nmol/L) (p = 0.02), which persisted after adjustments (p = 0.026), along with Sinhalese ethnicity (p < 0.001). VDD was significantly more prevalent in cases (83.7% vs. 71.2%; crude odds ratio (OR) = 2.1; 95% CI 1.1, 4.1); but was not an independent predictor of COVID-19 status (adjusted OR = 1.9; 95% CI 0.6, 5.7). A lower 25(OH)D level was observed in moderate/severe cases (median = 28.0; IQR = 20.4 nmol/L) vs. mild (median = 39.8; IQR = 19.0 nmol/L), however, neither low serum concentrations nor deficiency showed an independent relationship with severity (p > 0.05). Diabetes was the sole predictor of COVID-19 severity (p = 0.022). Vitamin D has potential as a primary preventive strategy in preventing COVID-19 like infections, but not as a secondary preventive strategy to reduce its severity.