Ślifirczyk, M., B. Jędrzejewska, A. Ślifirczyk, and G. Denisiuk. “Testing the Content of Vitamin A in Dietary Supplements”. Pedagogy and Psychology of Sport, vol. 5, no. 2, Feb. 2019, pp. 91-97, doi:10.12775/PPS.2015.05.02.006.