High-Dose Vitamin D Supplementation and Exercise Effects on Vitamin D Metabolites in Professional Football Players

This pilot study was designed to explore the combined effects of high-dose vitamin D₃ supplementation and acute physical exercise on vitamin D metabolism in professional football players. The study responds to growing scientific interest in understanding how vitamin D status influences performance, recovery, and muscle function in athletes. While most previous studies have focused on chronic, low-to-moderate supplementation, this trial examined the response to a single, pharmacological dose of cholecalciferol in a controlled experimental setting.

Study Design

The study employed a randomized, single-blind, placebo-controlled, parallel-group design. Participants were randomly assigned to one of two groups:

Supplementation Group (SGP) - received a single oral dose of 500,000 IU vitamin D₃ (Vigantol Oil, P&G Health, Germany);

Placebo Group (PGP) - received an identical amount of placebo (vegetable oil).

The supplementation was administered 48 hours before a standardized intra-squad football match (ISG), conducted under conditions simulating a competitive game. All players followed the same training schedule and diet during the study.

Participants

A total of 20 professional male football players (aged 18-35) from a Polish top-league club volunteered to participate. Inclusion criteria included active professional status, regular training participation, and no use of vitamin D or calcium supplements in the previous 3 months. Exclusion criteria included musculoskeletal injuries, metabolic disorders, or refusal to sign informed consent.

Measurements

Blood samples were collected at three time points:

T3: baseline (before supplementation),

T4: 48 hours post-supplementation (pre-match),

T5: immediately after the intra-squad game.

Serum concentrations of 25-(OH)D₃, 24,25-(OH)₂D₃, and 3-epi-25-(OH)D₃ were determined using LC-MS/MS. Additional biochemical variables (hemoglobin, glucose, testosterone, cortisol, ferritin, calcium, CK) were analyzed to monitor physiological status.

Outcomes

Primary Outcome: Changes in serum 25-(OH)D₃ concentrations after supplementation and exercise.

Secondary Outcomes: Changes in 24,25-(OH)₂D₃ and 3-epi-25-(OH)D₃ levels, metabolite ratios.

Ethics

The study was approved by the Ethics Committee of the Wroclaw University of Health and Sport Sciences (Resolution No. 1/2024, March 1, 2024). All participants signed written informed consent.

Inclusion criteria

• Male professional football players aged 18-35 years
• Actively training and competing in the Polish first football league
• No vitamin D or calcium supplementation during the previous 3 months
• No injuries or illnesses affecting participation

Exclusion criteria

• Current musculoskeletal injury or illness
• Chronic metabolic, endocrine, or renal disorders
• Use of vitamin D or calcium supplements
• Refusal or inability to sign informed consent