Time-point (T) measurements of 25(OH)D, blood parameters, and supplementation of vitamin D
MAY
The study design involved the measurements of 25(OH)D and blood parametersparameter concentration in blood plasma. Additionally, during the project, the number of sunny days (UV radiation) and the players’ diet were recorded. All the measurements were performed four times: MThe middle of September 2019 (T1), middle of December 2019 (T2), beginning of May 2020 (T3, the date was changed from the middle of March because of the COVD-19COVID-19 lockdown), and end of August 2020 (T4). Due to significant drops in the players’ 25(OH)D concentration, vitamin D supplementation was applied after T2. Therefore, the supplementation lasted from the middle of January to the middle of March (all preseason periods).