Vitamin D and SARS-CoV-2 infection—evolution of evidence supporting clinical practice and policy development

Vitamin D is a vitamin pro-hormone which can be taken exogenously from the diet or supplements, or can be synthesised cutaneously through the action of summer sunlight on skin as shown in Fig. 1 [ 1 ]. While oral intake is an important source of vitamin D, the major physiological source is UVB irradiation at a wavelength of 290–315 nm [ 2 ]. The ability of the skin to synthesise vitamin D is compromised at northerly latitudes, particularly amongst those who are older or who have dark skin pigmentation.