title: Prevalence of vitamin D inadequacy in athletes: a systematic-review and meta-analysis.
abstract: BACKGROUND
  Vitamin D is essential for maintaining optimal bone health. The prevalence of vitamin D inadequacy in athletes is currently unclear.
  
  
  OBJECTIVE
  The objective of this study is to determine the prevalence of vitamin D inadequacy in athletes.
  
  
  METHODS
  We conducted a systematic review and meta-analysis. Multiple databases were searched and studies assessing serum 25-hydroxyvitamin D [25(OH)D] status in athletes were identified. Serum 25(OH)D is measured to clinically determine vitamin D status. Reviewers independently selected the eligible articles, assessed the methodological quality, and extracted data. Disagreements were resolved by consensus. Weighted proportions of vitamin D inadequacy [serum 25(OH)D <32 ng/mL] were calculated (DerSimonian-Laird random-effects model) and compared using Chi-squared (χ (2)) test. Subgroup analyses were conducted and risk ratios (RRs) with 95 % confidence intervals (CIs) were reported.
  
  
  RESULTS
  Twenty-three studies with 2,313 athletes [mean (standard deviation) age 22.5 (5.0) years, 76 % male] were included. Of 2,313 athletes, 56 % (44-67 %) had vitamin D inadequacy that significantly varied by geographical location (p < 0.001). It was significantly higher in the UK and in the Middle East. The risk significantly increased for winter and spring seasons (RR 1.85; 95 % CI 1.27-2.70), indoor sport activities (RR 1.19; 95 % CI 1.09-1.30), and mixed sport activities (RR 2.54; 95 % CI 1.03-6.26). The risk was slightly higher for >40°N latitude [RR 1.14 (95 % CI 0.91-1.44)] but it increased significantly [RR 1.85 (1.35-2.53)] after excluding the Middle East as an outlier. Seven studies with 359 athletes reported injuries. The prevalence of injuries in athletes was 43 % (95 % CI 20-68) [bone related = 19 % (95 % CI 7-36); muscle and soft-tissue = 37.5 % (95 % CI 11.5-68.5)].
  
  
  CONCLUSIONS
  Despite the limitations of the current evidence, the prevalence of vitamin D inadequacy in athletes is prominent. The risk significantly increases in higher latitudes, in winter and early spring seasons, and for indoor sport activities. Regular investigation of vitamin D status using reliable assays and supplementation is essential to ensure healthy athletes. The prevalence of injuries in athletes is notable but its association with vitamin D status is unclear. A well-designed longitudinal study is needed to answer this possible association.
authors.affiliation: Department of Surgery, McMaster University, 39 Charlton Avenue East, Hamilton, ON, L9K 1S, Canada, farrokh@mcmaster.ca.
authors.forename: Forough
authors.initials: F
authors.lastname: Farrokhyar
authors.forename: Rasam
authors.initials: R
authors.lastname: Tabasinejad
authors.forename: Dyda
authors.initials: D
authors.lastname: Dao
authors.forename: Devin
authors.initials: D
authors.lastname: Peterson
authors.forename: Olufemi R
authors.initials: OR
authors.lastname: Ayeni
authors.forename: Reza
authors.initials: R
authors.lastname: Hadioonzadeh
authors.forename: Mohit
authors.initials: M
authors.lastname: Bhandari
mesh_terms: D000531:Altitude; D001265:Athletic Injuries / Q000453:epidemiology; D006801:Humans; D015995:Prevalence; D012307:Risk Factors; D012621:Seasons; D013177:Sports; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood; D014808:Vitamin D Deficiency / Q000453:epidemiology*
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D