Constantini, N. W., Livne, N., Moran, D., Raz, R., & Dubnov-Raz, G. (2012). Vitamin D supplementation and physical performance in adolescent swimmers. Presentation 2863 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.

"Serum vitamin D levels have been shown to correlate with several physical functions, such as muscle power, velocity and balance, mostly in the elderly and in sedentary populations. Vitamin D insufficiency is extremely prevalent in the general population, including athletes, yet its effect on performance is unknown."

This study evaluated the effect of vitamin D supplementation on swimming performance, power, and balance in young swimmers with vitamin D insufficiency. Competitive adolescent swimmers (age-groupers, M = 34, F = 20) with serum vitamin D levels below 30 ng/mL were randomly assigned to either an experimental or control group. The supplementation group received 2,000 IU/d of vitamin D3 drops for 12 weeks during a winter training season, and the control group received placebo drops identical in appearance and flavor. Freestyle swimming performance was assessed by a modification of the Mader test: 400m at V2-3 (below anaerobic threshold), 400m at V3-4 (above anaerobic threshold), and 4 x 50m all-out sprints. Swimming time and post-swim heart rates were measured for each stage of the test. Arm grip-strength was measured using a dynamometer; balance was measured using the unipedaled stance test twice (eyes open/closed). All measures were taken pre- and post-intervention.

Mean serum Vitamin D levels increased in the supplementation group and decreased in the control group during the study. There were no significant between-group differences in swimming time, heart rate, strength, or balance changes post-supplementation. No significant correlations were found between age-adjusted vitamin D changes in the whole study cohort, and changes in the measures of physical performance.

Implication. Vitamin D supplementation for 12 weeks to adolescent swimmers with vitamin D insufficiency did not affect swimming performance, power, and balance. Despite the widespread concern that vitamin D insufficiency might influence sport performance, there is currently no evidence that improving vitamin D status would benefit age-group athletes.

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