Interaction between age and vitamin D deficiency in severe COVID-19 infection.

Background: coronavirus disease 2019 (COVID-19) can induce an exaggerated inflammatory response. Vitamin D is a key modulator of the immune system. We hypothesized that vitamin D deficiency (VDD) could increase the risk of developing severe COVID-19 infection. Methods: patients with confirmed COVID-19 seen at the emergency department of our hospital with recent measurements of 25(OH)D were recruited. We explored the association of vitamin D deficiency (VDD), defined as 25-hydroxyvitamin D < 20 ng/mL, with a composite of adverse clinical outcomes. Results: we included 80 patients, of which 31 (39 %) presented the endpoint. VDD tended to predict an increased risk of developing severe COVID-19 after adjusting for age, gender, obesity, cardiac disease, and kidney disease [OR 3.2 (95 % CI: 0.9-11.4), p = 0.07]. Age had a negative interaction with the effect of VDD on the composite outcome (p = 0.03), indicating that the effect was more noticeable at younger ages. Furthermore, male gender was associated with VDD and with severe COVID-19 at younger ages. Conclusions: in this retrospective study, vitamin D deficiency showed a signal of association with severe COVID-19 infection. A significant interaction with age was noted, suggesting VDD may have a greater impact in younger patients. These findings should be confirmed in larger, prospective, adequately powered studies.