Vitamin D 25-Hydroxylase Deficiency

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.

The goal of this clinical trial is to evaluate whether a high-intensity loading dose of ergocalciferol (vitamin D2) can normalize blood vitamin D levels more rapidly and safely than standard weekly dosing in patients with newly diagnosed aggressive non-Hodgkin lymphoma. The study will also assess the safety of both dosing strategies. The main questions it aims to answer are: * Does a high-intensity loading dose of ergocalciferol lead to faster normalization of serum 25-hydroxyvitamin D levels compared with standard weekly dosing? * Are there differences in safety and adverse events between the two dosing strategies? Researchers will compare a high-intensity loading dose regimen of ergocalciferol with a standard weekly dosing regimen to determine differences in vitamin D normalization and safety outcomes. Participants will: * Be randomly assigned to receive either a high-intensity loading dose or a standard weekly dose of ergocalciferol (vitamin D2) * Receive standard first-line immunochemotherapy for aggressive non-Hodgkin lymphoma * Have blood tests to monitor vitamin D levels, calcium, phosphate, and safety parameters at scheduled visits * Be followed for treatment response, survival outcomes, and adverse events during and after therapy