Assessment of vitamin D concentration in non-supplemented professional athletes and healthy adults during the winter months in the UK: implications for skeletal muscle function

The current study implemented a two-part design to (1) assess the vitamin D concentration of a large cohort of non-vitamin D supplemented UK-based athletes and 30 age-matched healthy non-athletes and (2) to examine the effects of 5000 IU center dot day1 vitamin D3 supplementation for 8-weeks on musculoskeletal performance in a placebo controlled trial. Vitamin D concentration was determined as severely deficient if serum 25(OH)D<12.5nmol center dot l1, deficient 12.530nmol center dot l1 and inadequate 3050 nmol center dot l1. We demonstrate that 62% of the athletes (38/61) and 73% of the controls (22/30) exhibited serum total 25(OH)D<50nmol center dot l1. Additionally, vitamin D supplementation increased serum total 25(OH)D from baseline (mean +/- SD=29 +/- 25 to 103 +/- 25nmol center dot l1, P=0.0028), whereas the placebo showed no significant change (53 +/- 29 to 74 +/- 24nmol center dot l1, P=0.12). There was a significant increase in 10m sprint times (P=0.008) and vertical-jump (P=0.008) in the vitamin D group whereas the placebo showed no change (P=0.587 and P=0.204 respectively). The current data supports previous findings that athletes living at Northerly latitudes (UK=53 degrees N) exhibit inadequate vitamin D concentrations (<50 nmol center dot l1). Additionally the data suggests that inadequate vitamin D concentration is detrimental to musculoskeletal performance in athletes. Future studies using larger athletic groups are now warranted.