Vitamin D status in professional ballet dancers: Winter vs. summer
Objective: Serum 25-hydroxyvitamin D is produced by the exposure of the skin to sunlight. Therefore athletes who train indoors, such as dancers, are vulnerable to vitamin D deficiency. The purpose of the study was to evaluate the serum 25-hydroxyvitamin D status in UK professional dancers during periods of reduced and increased sunlight exposure (i.e., winter vs. summer), and to assess the impact on bone metabolism and risk of injury. Design: Cohort study. Methods: 19 elite classical ballet dancers (age 26 +/- 8.86 yr; height 1.66 +/- 8.84 m; mass 54.3 +/- 10.47 kg) were monitored over a 6 month period for 25-hydroxyvitamin D, PTH and blood serum bone turnover markers (CTX and PINP) along with injury data. Repeated measure ANOVA and Wilcoxon and Chi-square analyses were used and significance was set at p <= 0.05. Results: Significant changes were noted between the winter and summer test dates for 25-hydroxyvitamin D (14.9 ng/ml vs. 23.9 ng/ml; p < 0.001), PTH (38.7 pg/ml vs. 26.3 pg/ml; p < 0.001) and PINP (89.9 ng/ml vs. 67.6 ng/ml; p < 0.01). The oral contraceptive had a significant effect on serum 25-hydroxyvitamin D, PTH and CTX. Soft tissue injuries were significantly lower in summer compared to winter period (winter = 24, summer = 13; p < 0.05). Conclusions: Professional ballerinas characterized by a high incidence of low serum 25-hydroxyvitamin D levels which improve marginally in the summer. These dancers also demonstrate a higher injury incidence in the winter. Oral contraception seems to increase serum 25-hydroxyvitamin D levels and has a positive effect on bone metabolism. (C) 2013 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.