Book of Abstract ECSS 2025: 30th Annual Congress of the European College of Sport Science

MONITORING AND FOLLOW-UP OF VITAMIN D SUPPLEMENTATION: EFFECTS ON BLOOD MARKERS AND PERFORMANCE IN RUNNERS AND NON-RUNNERS DURING AUTUMN AND WINTER SEASON UNIVERSITÀ DEGLI STUDI DI URBINO INTRODUCTION: Recent interest in vitamin D’s role in musculoskeletal and immune health prompted this study to assess how 2 months of supplementation affects serum vitamin D status, performance, and leukocyte parameters in healthy runners and non-runners, with a subsequent 3-month follow-up. METHODS: Fifty-two participants were randomized into four groups—runners and non-runners, with or without daily sup plementation of 2000 IU vitamin D (administered as orodispersible films). Assessments were conducted at baseline (October, T0), after 2 months (T1), and 3 months post supplementation (T2). Measurements included blood tests (25 hydroxyvitamin D in ng/mL and leukocyte counts), VO₂max, maximal isometric force (MIF), and vertical jump (CMJ) perfor mance. Additionally, diet, training, local daily solar irradiation, and temperature were monitored. RESULTS: Diet and training remained stable over the study period. Weather conditions were consistently sunny, with an average temperature of 20.0 ± 1.7 °C, daily solar irradiation of 15745.8 ± 1033.7 W/m², and approximately 9.6 ± 0.8 hours of sunshine. Notably, both solar irradiation and temperature decreased significantly from October to January; thereafter, solar irradiation increased while temperature remained low until April. Supplemented runners showed a 20.82% increase in vitamin D (from 30.45 ± 7.0 to 35.35 ± 8.9 ng/mL, p<0.001), whereas non-supplemented runners did not exhibit a significant change at T1, and non-supplemented non-runners experienced a 32.23% decrease (from 25.93 ± 6.6 to 17.8 ± 7.3 ng/mL, p<0.001). At T2, vitamin D levels declined significantly in all groups (e.g., supplemented runners decreased from 35.35 ± 8.9 to 23.52 ± 5.6 ng/mL, p<0.001). Neutrophil counts varied significantly over time and by supplementation status (p=0.03): non-supplemented groups had progressive decreases (T0–T1: –12.37% and –14.50%; T0–T2:16.23% and –23.66%), while supplemented groups remained relatively stable (a slight increase at T1 followed by a non significant decrease at T2). No significant changes were observed in VO₂max or CMJ, although MIF improved modestly in supplemented groups. CONCLUSION: Two months of daily 2000 IU vitamin D supplementation effectively increased serum vitamin D levels and maintained stable leukocyte counts in both runners and non-runners. However, cessation led to significant declines by the 3-month follow-up, indicating that continued supplementation may be necessary. Interestingly, vitamin D levels in non supplemented subjects initially paralleled solar irradiation trends until January; subsequently, despite an increase in solar irradiation, persistently low temperatures appeared to sustain the decline in vitamin D levels. While supplementation improved vitamin D status and moderated immune responses, it did not affect VO₂max or CMJ, and the modest improvement in MIF warrants further investigation.