Subjects were randomized to two groups: the experimental one, n = 20 and the placebo one, n = 20 with the same age, experience in running and 25(OH)D level. The experimental group received vitamin D3 supplementation (around 10,000 UI/day, i.e., 20 droplets -Vigantol medicament, Merck) and the control group received a placebo (20 droplets of sunflower oil, placed in an identical bottle as vitamin D3) for two weeks before a run. The last vitamin D dose was taken 24 h before the 100 km ultra-marathon. 40 male athletes took part in the 100 km ultra-marathon. Blood was collected before (day 0) and after supplementation (day 14). Next (day 15): before, after 25, 50, 75,100 km running and 12 hours after the run (day 16). The data were subjected to statistical analysis.
A group of runners received vitamin D (10,000 IU - international unit per day) for two weeks. The aim of the intervention was to check the effect of vitamin D supplementation on selected parameters of inflammation and iron metabolism in comparison with the placebo group. Blood was collected before and after supplementation. Next: before, after 25, 50, 75,100 km running and 12 hours after the run. The data were subjected to statistical analysis.