The Associations of Vitamin D Status with Athletic Performance and Blood-borne Markers in Adolescent Athletes: A Cross-Sectional Study

TL;DR

In 47 male adolescent Taekwondo athletes, 74.5% had vitamin D insufficiency or deficiency, but vitamin D status showed no significant group effects on athletic performance or blood-borne markers. Serum 25(OH)D was weakly positively correlated with Wingate mean power and relative mean power after covariate adjustment, but was not a significant predictor of athletic performance in multiple regression.

Key findings

• Serum 25(OH)D ranged from 16 to 73.25 nmol/L, and 74.5% of the adolescent Taekwondo athletes had vitamin D deficiency or insufficiency.
• Vitamin D status groups showed no significant differences in any athletic performance variable or in blood-borne markers (free testosterone, cortisol, creatine kinase, urea).
• After adjusting for bone age, height, weight, training experience, lean body mass, and fat mass, 25(OH)D was positively correlated with mean power output (r = 0.359, p < 0.05) and relative mean power output (r = 0.325, p < 0.05), but not with other performance-related factors or blood-borne markers.
• Multiple linear regressions indicated that 25(OH)D concentration was not a significant predictor of athletic performance; free testosterone correlated with mean power output (r = 0.291, p < 0.05), vertical jump (r = 0.378, p < 0.01), and agility T-test (r = −0.381, p < 0.01), while cortisol correlated with relative mean power output (r = −0.438, p < 0.01) and VO2max (r = −0.317, p < 0.05).

Methods

• Cross-sectional study of 47 male adolescent Taekwondo athletes aged 15–18 years (mean age 16.7 ± 0.84 years; training experience 53.4 ± 10.60 months), conducted during the in-season period in November in Gyeonggi-do, Republic of Korea.
• Athletic performance was assessed with a graded maximal exercise test (VO2max), Wingate anaerobic power test, vertical jump, agility T-test, isokinetic knee muscle strength, and an eccentric contraction fatigue protocol; blood samples measured serum 25(OH)D, free testosterone, cortisol, creatine kinase, and urea, and 3-day dietary records were collected.
• Analyses included one-way ANOVAs with Bonferroni-adjusted alpha of 0.02 (0.05/3), Pearson and partial correlation analyses, and multiple linear regressions adjusted for skeletal maturation (bone age), height, weight, training experience, lean body mass, and fat mass.

Limitations

• Stated by the authors: a comparative lack of sample size across vitamin D status groups (deficient n = 5, insufficient n = 30, adequate n = 12), time points of measurement, and the specific population limit the study’s representativeness; future work should consider weather conditions, age groups, stress-to-recovery status, training status, seasonal variation, location, ethnicity, and ages.
• Evident from the text: the cross-sectional design cannot establish causality, and the findings are limited to male adolescent Taekwondo athletes at one location during one in-season November period, so generalizability is narrow.
• Evident from the text: the authors note that the mechanisms by which vitamin D may influence anaerobic performance remain unclear, and the weak correlation was not supported by significant regression prediction.