Sunlight exposure is the primary source of vitamin D in humans (Scientific Advisory Committee on Nutrition [SACN], 2016), but vitamin D deficiency is common worldwide (Bouillon et al, 2019; Mendes et al, 2020). Measures to contain the recent spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and to help prevent the Covid-19 disease caused by the SARS-CoV-2 virus may increase rates of vitamin D deficiency, as selfisolation is likely to prevent people from gaining adequate exposure to sunlight to meet their vitamin D requirement if they do not have a garden or balcony.