evidence: In view of the enormous health implications of the coronavirus disease 19 (COVID-19) pandemic caused by the worldwide spread of severe acute respiratory syndrome coronavirus 2, a possible link with poor vitamin D status and the risk or severity of COVID-19 has received great attention. Seven studies so far compared serum 25OHD concentrations in patients with COVID-19 compared with individuals without COVID-19 (ref.87) and found a lower level (mean difference of about 12 nmol/l) in patients with COVID-19; however, in many studies the sampling did not take place at the same time in both groups. In addition, these studies were unable to control for confounding factors, a major problem due to the large number of similarities in the risk factors for vitamin D deficiency and COVID-19. About 31 studies looked at a possible link between vitamin D status and severity of the outcome of COVID-19. Lower serum concentrations of 25OHD were associated with greater mortality, greater need for intensive care treatment or increased severity of illness in general compared with better vitamin D status. However, this finding was based on observational studies. [...] Bassatne, A. et al. The link between COVID-19 and vitamin D (VIVID): a systematic review and meta-analysis. Metabolism119, 15475 (2021). [...] Butler-Laporte, G. et al. Vitamin D and COVID-19 susceptibility and severity in the COVID-19 Host Genetics Initiative: a Mendelian randomization study. PLoS Med.18, e1003605 (2021).