Dudnyk, Veronika, and Valeriia Demianyshyna. “Assessment of Severity of Cystic Fibrosis in Children Depending on the Vitamin D Status”. Journal of Education, Health and Sport 10, no. 9 (September 22, 2020): 561–568. Accessed May 18, 2025. https://apcz.umk.pl/JEHS/article/view/JEHS.2020.10.09.068.