Vitamin D Deficiency/Insufficiency

This study aims to evaluate the effects of high-dose vitamin D3 supplementation on selected physiological, neuromuscular, and cognitive parameters in athletes. At the baseline visit, participants will undergo a series of assessments at the Functional Research Laboratory at AWF Katowice, including a 10 mL venous blood sample collection, body composition analysis (via InBody and DEXA scans), neuromuscular function evaluation using tensiomyography (TMG), and computerized cognitive tests via the Vienna Test System. Following baseline testing, participants will be randomly assigned to either the vitamin D3 group or the placebo group. The active group will receive a daily dose of 4,000 IU of vitamin D3 (1 capsule with dinner), while the control group will receive an identical placebo. The intervention period will last for 4 or 8 weeks. Upon completion of the supplementation period, all baseline assessments will be repeated to evaluate the post-intervention changes.