Tan, Margarita Katrina Amor, et al. “Association of Vitamin D Levels on the Clinical Outcomes of Patients Hospitalized for COVID-19 in a Tertiary Hospital”. Journal of the ASEAN Federation of Endocrine Societies, vol. 38, no. 1, Feb. 2023, pp. 81-89, doi:10.15605/jafes.038.01.07.