title: Vitamin D and exercise performance in professional soccer players.
abstract: OBJECTIVE
  The current study had two aims. The primary purpose was to examine the association between serum vitamin D levels and the ergometric evaluation of muscle strength, aerobic capacity, and speed in professional soccer players. The secondary aim was to evaluate the effects of the soccer off-season period on serum vitamin D levels.
  
  
  METHODS
  Sixty-seven Caucasian male soccer players (age 25.6 ± 6.2 and height 1.81 ± 0.08 m), members of two Greek Superleague Soccer teams and one Football-league championship team participated in this study. Exercise performance testing for the determination of squat jump (SJ), countermovement jump (CMJ), 10 (10 m) and 20 meters (20 m) sprint performance, maximal oxygen consumption (VO2max), anthropometry, and blood sampling were performed before (pre) and after (post) the six-week off-season period.
  
  
  RESULTS
  Analysis of our results showed the following: (a) a significant correlations between serum vitamin D levels and performance parameters in both pre (SJ; P < 0.001, CMJ; P < 0.001, VO2max; P < 0.001, 10 m; P < 0.001, and 20 m; P < 0.001) and post (SJ; P < 0.001, CMJ; P<0.001, VO2max; P = 0.006, 10 m; P < 0.001, and 20 m; P < 0.001) experimental sessions. (b) Vitamin D concentration increased significantly (P < 0.001) following the six-week off-season period compared to baseline, while at the same time all measured performance parameters decreased (SJ; P < 0.001, CMJ; P < 0.001, 10 m; P < 0.001, 20 m; P < 0.001, VO2max; P<0.001).
  
  
  CONCLUSIONS
  Our findings suggest that vitamin D levels are associated with the ergometric evaluation of muscle strength, as expressed by SJ and CMJ, sprinting capacity, and VO2max in professional soccer players, irrespective the levels of performance. Furthermore, our data reaffirm the importance of UVB on serum vitamin D levels. Moreover, reductions in exercise training stress may also have beneficial effects on vitamin D levels, suggesting a possible association of its levels and the training-induced stress. Our results indicate a possibly bidirectional interaction between soccer performance indices and vitamin D levels.
authors.affiliation: Department of Clinical Chemistry, School of Medicine, University of Crete, Heraklion, Greece.
authors.forename: Nikolaos E
authors.initials: NE
authors.lastname: Koundourakis
authors.affiliation: Department of Laboratory Haematology, University Hospital, Heraklion, Crete, Greece.
authors.forename: Nikolaos E
authors.initials: NE
authors.lastname: Androulakis
authors.affiliation: Departments of Clinical Chemistry, University of Crete, School of Medicine, and University Hospital, Heraklion, Greece.
authors.forename: Niki
authors.initials: N
authors.lastname: Malliaraki
authors.affiliation: Departments of Clinical Chemistry, University of Crete, School of Medicine, and University Hospital, Heraklion, Greece.
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Margioris
mesh_terms: D000328:Adult; D000886:Anthropometry; D054874:Athletic Performance / Q000502:physiology*; D006115:Greece; D006801:Humans; D008297:Male; D053580:Muscle Strength; D010101:Oxygen Consumption; D012916:Soccer / Q000502:physiology*; D014807:Vitamin D / Q000097:blood*
chemical_list: D014807:Vitamin D