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.
a minimum of 8 years of training experience,
absence of injuries in the 6 months leading up to the assessments,
consistent engagement in training sessions a minimum of 5 times per week over the last 6 months.
vitamin D supplementation within one month prior to the study,
use of multivitamin supplements,
intestinal disorders.
Crossover
Vitamin D supplementation
Dietary supplementVitamin D3 will be administered orally in the form of capsules. Participants will ingest a total daily dose of 4,000 IU, split into two doses: 1 capsule (4,000 IU) in the evening with dinner. The intervention will be carried out daily for a duration of either 4 or 8 weeks. Supplementation compliance will be monitored by the research team through capsule counting during follow-up visits.
Placebo
Dietary supplementAn identical placebo will be administered orally in the form of capsule, matching the active vitamin D3 supplement in appearance, size, color, and taste. Participants will ingest 1 placebo capsule in the evening with dinner daily for a duration of either 4 or 8 weeks.
Serum 25-Hydroxyvitamin D Concentration
Description: Serum concentration of 25-hydroxyvitamin D \[25(OH)D\] measured using a validated laboratory method to assess vitamin D status. Unit of Measure: ng/mL
Corsi Block-Tapping Test - Block Time
Description: Visuospatial working memory assessed using the Corsi Block-Tapping Test. Block Time represents the reaction time required to complete the task. Unit of Measure: ms
Corsi Block-Tapping Test - Reverse Span Score
Description: Visuospatial working memory performance assessed using the reverse recall condition of the Corsi Block-Tapping Test. Unit of Measure: score
Corsi Block-Tapping Test - Unweighted Block Span
Description: Maximum sequence length correctly reproduced during the Corsi Block-Tapping Test. Unit of Measure: blocks
Countermovement Jump Height
Description: Lower-body explosive power assessed using the Countermovement Jump (CMJ) test. Unit of Measure: cm
Sprint Performance
Description: Sprint performance assessed during a short-distance sprint test. Unit of Measure:s
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