Walczak, K., Walczak, P., Zdun, S., Nemeczek, S., Merkisz, K., Grzybowski, J., Marciniak, A., Grzywna, N., Jaskuła, K. and Orłowski, W. 2023. Effect of vitamin D on the course of COVID-19 infection. Journal of Education, Health and Sport. 13, 2 (Jan. 2023), 261–267. DOI:https://doi.org/10.12775/JEHS.2023.13.02.038.