This study was a randomized controlled trial aimed to test whether vitamin D (VD) supplementation affects measures of physical performance in VD-insufficient mildly trained children (1). Thirty-six recreationally soccer player boys were randomly assigned to single dose (200,000 IU) of VD3 or placebo. Plasma 25-hydroxyvitamin D (25-OHD) was assessed and measures of physical performance (i.e. vertical and standing broad jumps, triple hop, 10-m and 30-m sprints, shuttle run) were performed before and 12 weeks after the loading dose. Baseline 25-OHD and physical variables were equivalent in the two groups. The results showed that twelve weeks after VD loading, plasma 25-OHD increased and physical variables improved in VD group, only. There was a significant interaction effects for group by time for vertical jump, triple hop jump, 10-m and 30-m sprints, and shuttle run. The authors conclude that a single bolus of VD3 resulted in significant improvements in jumping ability, agility, and running speed in VD-insufficient mildly trained children. The findings suggest that correcting VD deficit might be beneficial for physical performance.