Vitamin D status: a U-shaped relationship for SARS-CoV-2 seropositivity in UK healthcare workers oleh Aaron Scott, Sebastian T Lugg, Dhruv Parekh, David R Thickett, Martin Hewison, Craig Webster, Sian E Faustini, Alex G Richter, Adrian M Shields, Aduragbemi A Faniyi, William R Mackay, Joanne E Duffy