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Ibrahim Elmi, Zakaria Ali, Sighakoli, Sameer, Tetteh, John and Zand Fard, Nazanin ORCID: 0000-0003-2058-2354 (2023) Case–control study of serum vitamin D concentrations in hospitalised patients with COVID-19 and hospitalised controls suffering with respiratory tract infections of differing aetiology. BMJ, Nutrition, Prevention and Health:e000428. pp. 1-7. ISSN 2516-5542 (Online) (doi:https://doi.org/10.1136/bmjnph-2022-000428)