The effect of L-theanine supplementation on the immune system of athletes exposed to strenuous physical exercise - Juszkiewicz, A.; Glapa, A.; Basta, P.; Petriczko, E.; Zolnowski, K.; Machalinski, B.; Trzeciak, J.; Luczkowska, K.; Skarpanska-Stejnborn, A. (Journal of the International Society of Sports Nutrition, 2019)