The effects of 4 weeks vitamin D3 supplementation on athletic performance

BACKGROUND: Vitamin D deficiency is a growing pandemic worldwide. Growing evidence in the elderly has shown that individuals with a higher vitamin D status (>75nmol/L) exhibit improved musculoskeletal performance. However it is unknown whether improving vitamin D status in athletes’ leads to improved athletic performance. PURPOSE: To investigate the effects of 4 weeks vitamin D3 supplementation on a number of indicators of aerobic and anaerobic performance as well as muscle strength. METHODS: 36 endurance trained male cyclists/triathletes (Age 39±8y, Height 1.80±0.66m, Weight 76.3±6.2kg, VO2 max 60.0±3.8 ml/kg/min) were recruited and randomly assigned into one of four supplementation groups: Placebo (PLA), 1500IU D3/d, 3000IU D3/d and 6000IU D3/d, lasting for 4 weeks, as part of a double blind study design. Athletes reported to the lab for 2 days of performance testing pre and post supplementation, including VO2 max test, 1 repetition max single leg strength test (1RM), maximal voluntary contraction hand grip test, 1 hour time trial and repeated Wingate tests. All data collection was performed at latitude of 52°29’N, between December and March. RESULTS: Pre supplementation, 53% and 33% of athletes were vitamin D deficient (>50 nmol/L) and insufficient (50-75 nmol/L) respectively. Vitamin D supplementation caused 25(OH)D to increase to a sufficient status (>75 nmol/L), while those receiving PLA saw small non significant changes to 25(OH)D. Small significant improvements in 1 RM leg extension for those athletes receiving 6000IU were observed on both the dominant (5.3±1.4kg (6000IU) and 2.0±1.9kg (PLA) p<0.05) and non dominant leg (5.8±1.0kg (6000IU) and 1.5±1.8kg (PLA) p<0.05). Furthermore there was a tendency for peak power output to improve during the wingate test for 3000IU/d and 6000IU/d, however this difference did not reach significance. For the remaining performance tests no difference was observed. CONCLUSIONS:The study shows that 4 weeks vitamin D supplementation, above the currently debated IOM RDI 600IU/d, can improve vitamin D status in athletes. Small significant improvements in 1RM leg extension performance were observed at the highest dose. Based on these results it could be argued that the potential benefits of vitamin D to athletic performance may be specific to resistance based exercise.