Vitamin D supplementation and COVID-19 risk: A Population-based Cohort Study

Oristrell, J., Oliva, J.C., Casado, E. et al, J Endocrinol Invest 45, 167-179 (2022) 

This large, population-based study observed that  "Patients on cholecalciferol treatment achieving 25OHD levels ≥ 30 ng/ml had lower risk of SARSCoV2 infection, lower risk of severe COVID19 & lower COVID-19 mortality than unsupplemented 25OHD-deficient patients ..."

https://doi.org/10.1007/s40618-021-01639-9