Effects of High-Dose Vitamin D on Hormones, Neuromuscular Function, Cognition, and Body Composition in Athletes

The Effect of High-dose Vitamin D Supplementation on Selected Hormone Concentrations, Neuromuscular Transmission, Athletic Performance, Cognitive Functions, and Body Composition in Athletes.

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.

Study Overview

• Status: Recruiting
• Conditions: Vitamin D Deficiency/Insufficiency; Vitamin D 25-Hydroxylase Deficiency
• Intervention / Treatment: Dietary supplement: Vitamin D supplementation; Dietary supplement: Placebo

Detailed Description

For the first visit, the participant is invited to the Functional Research Laboratory at the Academy of Physical Education (AWF) in Katowice. The visit will be initiated with a blood sample collection (10 mL) from the cubital vein, which will be followed by body mass and body composition measurements. These measurements will be performed using the InBody device (in a standing position, in light clothing or underwear) and a DEXA scan (in a supine position, in light clothing), which is utilized to evaluate bone and fat tissue using a minimal dose of X-ray radiation.

As the next stage, a tensiomyographic (TMG) assessment will be conducted in a supine position and in underwear. Single-use electrodes will be attached to the biceps brachii (long head) of both upper limbs and the gastrocnemius (lateral head) of both lower limbs. A completely non-invasive, very low-voltage and low-intensity electrical current will be emitted by an electrostimulator in order to induce muscle contraction and measure its response speed. This assessment will be performed at rest, without a warm-up, is entirely harmless, and can be repeated.

Subsequently, cognitive function tests will be performed using the computerized Vienna Test System (SCHUHFRIED GmbH, Austria). The first test involves reading color-words and naming colors, while the second test involves reading words in an incongruent color and naming colors with an incongruent meaning. Responses will be provided by pressing one of four buttons on a specialized keyboard (time limit: 2500 ms per trial). Each diagnostic block (60 trials) will be preceded by a practice block (10 trials).

Following the completion of all assessments, the participant will be randomly assigned to one of two groups: the supplemented group (vitamin D3) or the placebo group. The randomization into groups will be carried out using balls placed in a black bag. Depending on the assigned group, and once the 25(OH)D3 level results are obtained by the research team (the next business day), the supplement in an appropriate dose or a placebo product will be allocated. The collection of the products will take place on the 3rd day from the start of the project. The dose of vitamin D3 will be of 4,000 IU/day. If assignment to the placebo group occurs during randomization, a placebo supplement will be provided. The supplements will be consumed 1 capsule in the evening (with dinner). The supplementation period will last for 4 or 8 weeks.

After 4 or 8 weeks of supplementation, the study will be concluded, at which point the participant will be invited to AWF again, where all assessments from stage 1 will be repeated.

• Study Type: Interventional
• Enrollment (Estimated): 200
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Małgorzata Michalczyk, Profesor; Phone Number: +48535016532; Email: m.michalczyk@awf.katowice.pl
• Study Contact Backup: Name: Małgorzata Michalczyk, Profesor; Phone Number: 535016532; Email: m.michalczyk@awf.katowice.pl

Study Locations

• Poland
  • Mikołowska 72a
    • Katowice, Mikołowska 72a, Poland, 40-065
      • Recruiting
      • The Jerzy Kukuczka Academy of Physical Education in Katowice
      • Contact: Małgorzata Michalczyk; Phone Number: 535016532; Email: m.michalczyk@awf.katowice.pl

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child; Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• 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.

Exclusion Criteria:

• vitamin D supplementation within one month prior to the study,
• use of multivitamin supplements,
• intestinal disorders.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Vitamin D3 supplemented group; Participants in this arm will receive vitamin D3 supplementation at a total daily dose of 4,000 IU. The supplement will be administered 1 capsule in the evening (with dinner). The intervention period will last for either 4 or 8 weeks.	Dietary supplement: Vitamin D supplementation; Vitamin 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 Comparator: Placebo supplementation group; Participants in this arm will receive placebo supplementation. The supplement will be administered capsule in the evening (with dinner). The intervention period will last for either 4 or 8 weeks.	Dietary supplement: Placebo; An 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.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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	8-weeks

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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	8-weeks
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	8-weeks
Corsi Block-Tapping Test - Unweighted Block Span	Description: Maximum sequence length correctly reproduced during the Corsi Block-Tapping Test. Unit of Measure: blocks	8-weeks

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Countermovement Jump Height	Description: Lower-body explosive power assessed using the Countermovement Jump (CMJ) test. Unit of Measure: cm	8-weeks
Sprint Performance	Description: Sprint performance assessed during a short-distance sprint test. Unit of Measure:s	8-weeks

Collaborators and Investigators

• Sponsor: The Jerzy Kukuczka Academy of Physical Education in Katowice

Study record dates

Study Major Dates

• Study Start (Actual): July 1, 2025
• Primary Completion (Actual): July 10, 2025
• Study Completion (Estimated): December 31, 2028

Study Registration Dates

• First Submitted: May 20, 2026
• First Submitted That Met QC Criteria: June 8, 2026
• First Posted (Actual): June 11, 2026

Study Record Updates

• Last Update Posted (Actual): June 11, 2026
• Last Update Submitted That Met QC Criteria: June 8, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: vitamin D; athletes; performance; hormones; speed; coggnitive function; neuro-muscular function
• Additional Relevant MeSH Terms: Nutrition Disorders; Avitaminosis; Deficiency Diseases; Malnutrition; Nutritional and Metabolic Diseases; Vitamin D Deficiency; Vitamin D Hydroxylation-Deficient Rickets, Type 1B
• Other Study ID Numbers: KB-05/2017; Institute of Sport Sciences (Other Identifier: The Jerzy Kukuczka Academy of Physical Education in Katowice)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Sharing Time Frame: Start data- 20.05.2026 End- 31.12.2028
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No