Impact of Vitamin D Status on Speed, Power, and Sport-Specific Skills in Young Soccer Players Living Above 55° North Latitude.

BACKGROUND: Vitamin D is crucial for calcium metabolism, protein and hormone synthesis, and immune response. Deficiency may impair muscle function and athletic performance, but evidence on sport‑specific skills and power remains inconsistent. METHODS: We studied 170 soccer players aged 7-18 from a region above 55°N. In February 2024, serum 25‑hydroxy-vitamin D (25[OH]D) was measured by mass spectrometry, and physical performance tests (sprint, jumps, change‑of‑direction) were conducted. Players were compared by vitamin D status (normal, insufficient, deficient) and by 25th vs. 75th percentiles. Statistical analyses included group comparisons, correlations, and multivariable linear regression adjusted for age, body size, maturation, and supplementation, with false discovery rate correction. RESULTS: No significant differences in performance were found between vitamin D groups, except for broad jump in unadjusted comparisons. Crude correlations were weak. In adjusted regression models, 25(OH)D was not significantly associated with any performance outcome; this was consistent across alternative models and after correction for multiple testing. CONCLUSIONS: In young soccer players above 55°N, vitamin D insufficiency and deficiency were common, but adjusted analyses did not provide robust evidence that 25(OH)D independently influences speed, power, or sport‑specific skills.