title: Low serum 25-hydroxyvitamin D is associated with increased risk of stress fracture during Royal Marine recruit training.
abstract: The aim of this study was to investigate vitamin D status and stress fracture risk during Royal Marine military training. Poor vitamin D status was associated with an increased risk of stress fracture. Vitamin D supplementation may help to reduce stress fracture risk in male military recruits with low vitamin D status.
  
  
  BACKGROUND
  Stress fracture is a common overuse injury in military recruits, including Royal Marine (RM) training in the UK. RM training is recognised as one of the most arduous basic training programmes in the world. Associations have been reported between serum 25-hydroxyvitamin D (25(OH)D) and risk of stress fracture, but the threshold of 25(OH)D for this effect remains unclear. We aimed to determine if serum 25(OH)D concentrations were associated with stress fracture risk during RM training.
  
  
  METHODS
  We prospectively followed 1082 RM recruits (males aged 16-32 years) through the 32-week RM training programme. Troops started training between September and July. Height, body weight and aerobic fitness were assessed at week 1. Venous blood samples were drawn at weeks 1, 15 and 32. Serum samples were analysed for 25(OH)D and parathyroid hormone (PTH).
  
  
  RESULTS
  Seventy-eight recruits (7.2 %) suffered a total of 92 stress fractures. Recruits with a baseline serum 25(OH)D concentration below 50 nmol L(-1) had a higher incidence of stress fracture than recruits with 25(OH)D concentration above this threshold (χ(2) (1) = 3.564, p = 0.042; odds ratio 1.6 (95 % confidence interval (CI) 1.0-2.6)). Baseline serum 25(OH)D varied from 47.0 ± 23.7 nmol L(-1) in February, to 97.3 ± 24.6 nmol L(-1) in July (overall mean 69.2 ± 29.2 nmol L(-1), n = 1016). There were weak inverse correlations between serum 25(OH)D and PTH concentrations at week 15 (r = -0.209, p < 0.001) and week 32 (r = -0.214, p < 0.001), but not at baseline.
  
  
  CONCLUSIONS
  Baseline serum 25(OH)D concentration below 50 nmol L(-1) was associated with an increased risk of stress fracture. Further studies into the effects of vitamin D supplementation on stress fracture risk are certainly warranted.
authors.affiliation: Environmental Medicine and Science, Institute of Naval Medicine, Cresent Road, Alverstoke, Gosport, PO12 2DL, UK. trish@trishdavey.co.uk.
authors.forename: T
authors.identifier: http://orcid.org/0000-0003-4820-5593
authors.initials: T
authors.lastname: Davey
authors.affiliation: Department of Nutritional Sciences, School of Biosciences and Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey, GU2 7XH, UK.
authors.forename: S A
authors.initials: SA
authors.lastname: Lanham-New
authors.affiliation: Environmental Medicine and Science, Institute of Naval Medicine, Cresent Road, Alverstoke, Gosport, PO12 2DL, UK.
authors.forename: A M
authors.initials: AM
authors.lastname: Shaw
authors.affiliation: University of Chichester, College Lane, Chichester, West Sussex, PO19 6PE, UK.
authors.forename: B
authors.initials: B
authors.lastname: Hale
authors.affiliation: Environmental Medicine and Science, Institute of Naval Medicine, Cresent Road, Alverstoke, Gosport, PO12 2DL, UK.
authors.forename: R
authors.initials: R
authors.lastname: Cobley
authors.affiliation: Specialist Assay Laboratory, Clinical Biomechemistry, Manchester Royal Infirmary, Manchester, M13 9WL, UK.
authors.forename: J L
authors.initials: JL
authors.lastname: Berry
authors.affiliation: Clinical Laboratory Services, University Hospitals Birmingham NHS Foundation Trust, Queen Elizabeth Hospital, Birmingham, B15 2WB, UK.
authors.forename: M
authors.initials: M
authors.lastname: Roch
authors.affiliation: Environmental Medicine and Science, Institute of Naval Medicine, Cresent Road, Alverstoke, Gosport, PO12 2DL, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Allsopp
authors.affiliation: Environmental Medicine and Science, Institute of Naval Medicine, Cresent Road, Alverstoke, Gosport, PO12 2DL, UK.
authors.forename: J L
authors.initials: JL
authors.lastname: Fallowfield
mesh_terms: D000293:Adolescent; D000328:Adult; D000886:Anthropometry / Q000379:methods; D016022:Case-Control Studies; D015775:Fractures, Stress / Q000097:blood / Q000209:etiology*; D006801:Humans; D008297:Male; D008889:Military Personnel / Q000706:statistics & numerical data*; D009784:Occupational Diseases / Q000097:blood / Q000209:etiology*; D010281:Parathyroid Hormone / Q000097:blood; D064797:Physical Conditioning, Human / Q000009:adverse effects* / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology; D011446:Prospective Studies; D012307:Risk Factors; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000150:complications*; D055815:Young Adult
chemical_list: D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D
keywords: 25(OH)D; Bone; Military; Physical training; Stress fracture; Vitamin D