Vitamin D Supplementation and Physical Performance in Adolescent Swimmers.

It is hypothesized that vitamin D insufficiency in athletes might negatively affect sport performance. The objective of this study was to examine the effect of vitamin D3 supplementation on physical performance of adolescent swimmers with vitamin D insufficiency. Fifty-three adolescent competitive swimmers with vitamin D insufficiency (serum 25-hydroxyvitamin-D concentrations (25(OH)D) < 30 ng/ml, mean 24.2 ± 4.8 ng/ml) were randomized to receive 2,000 IU/day of vitamin D3 or placebo for 12 weeks. Swimming performance at several speeds, arm-grip strength, and one-legged balance, were measured before and after supplementation. The age-adjusted changes in performance variables during the study were compared between groups. 25(OH) D concentrations at study end were significantly higher in the vitamin group compared with the placebo group (29.6 ± 6.5 ng/ml vs. 20.3 ± 4.2 ng/ml, p < .001), yet only 48% of the vitamin group became vitamin D sufficient with this dosing. No between-group differences were found in the changes of the performance variables tested. No significant differences in performance were found between participants that became vitamin D sufficient, and those who did not. No significant correlation was found between the change in serum 25(OH)D and age-adjusted balance, strength or swimming performance at study end. Vitamin D3 supplementation that raised serum 25(OH)D concentrations by a mean of 9.3 ng/ml above placebo in adolescent swimmers with vitamin D insufficiency, did not improve physical performance more than placebo.

Vitamin D concentrations and physical performance in competitive adolescent swimmers.

Serum vitamin D concentrations (25[OH]D) are associated with physical performance in the general population, but few studies have been published in athletes. 80 competitive adolescent swimmers from both sexes were tested for serum 25(OH)D concentrations, grip strength, balance and swimming performance at several speeds. Spearman's correlations were used to examine the associations between 25(OH)D concentrations and age-adjusted measures of performance. Performance parameters were also compared between vitamin D sufficient (n = 27), insufficient (25[OH]D ranging 20-29.9 ng/ml, n = 42), and deficient (25[OH]D < 20 ng/ ml, n = 11) participants. No significant associations were found between serum 25(OH)D concentrations and any of the performance measures, with no significant differences found between vitamin D sufficient, insufficient and deficient participants. In competitive adolescent swimmers, serum vitamin D concentrations were not associated with strength, balance or swimming performance. Vitamin D insufficient/deficient swimmers did not have reduced performance.