title: Skeletal and hormonal responses to sunlight deprivation in Antarctic expeditioners.
abstract: Serum 25(OH)D levels decline without sunlight exposure. We studied 120 expeditioners to Antarctica to determine the skeletal and hormonal responses to sunlight deprivation. With emerging vitamin D insufficiency, serum calcium decreased, PTH increased, and bone loss at the proximal femur was observed. Baseline serum 25(OH)D levels >100 nmol/L prevented vitamin D insufficiency.
  
  
  BACKGROUND
  Vitamin D stores deplete without adequate sunlight exposure unless supplementation is provided. We studied 120 healthy adults who spent a year in Antarctica as a model for sunlight deprivation to define the timing and magnitude of the skeletal and hormonal responses to emerging vitamin D insufficiency.
  
  
  METHODS
  Fasting blood samples were assessed at baseline, 6 and 12 months for serum 25-hydroxyvitamin D (25(OH)D), osteocalcin (OC), bone formation (P1NP) and resorption (CTx), PTH and calcium. Lumbar spine and proximal femur BMD was measured using DXA. Differences over time were determined using repeated measures ANOVA. Percent changes were expressed as (Delta value/(value A + value B)/2) x 100. Relationships between outcome measures were determined using Spearman's correlations.
  
  
  RESULTS
  Vitamin D insufficiency (<50 nmol/L) was observed in 85% of expeditioners by 6 months when serum calcium decreased and PTH increased (p < 0.01). By 12 months, OC increased by 7.4 +/- 3.0% (p < 0.05), and BMD decreased by 1.0 +/- 2.0% at the total proximal femur (p < 0.05). For those with vitamin D sufficiency at baseline (>50 nmol/L), sunlight deprivation produced vitamin D insufficiency within 4 months unless baseline values were >100 nmol/L.
  
  
  CONCLUSIONS
  Supplementation may be necessary for expeditioners with limited access to UV light.
authors.affiliation: Austin Health, University of Melbourne, West Heidelberg, Australia. sandraib@unimelb.edu.au
authors.forename: S
authors.initials: S
authors.lastname: Iuliano-Burns
authors.forename: X F
authors.initials: XF
authors.lastname: Wang
authors.forename: J
authors.initials: J
authors.lastname: Ayton
authors.forename: G
authors.initials: G
authors.lastname: Jones
authors.forename: E
authors.initials: E
authors.lastname: Seeman
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D000864:Antarctic Regions / Q000453:epidemiology; D015415:Biomarkers / Q000097:blood; D001862:Bone Resorption / Q000453:epidemiology / Q000209:etiology; D001842:Bone and Bones / Q000378:metabolism*; D019587:Dietary Supplements; D005215:Fasting / Q000097:blood; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015675:Osteocalcin / Q000097:blood*; D010281:Parathyroid Hormone / Q000097:blood; D011446:Prospective Studies; D013472:Sunlight; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood* / Q000150:complications; D055815:Young Adult
chemical_list: D015415:Biomarkers; D010281:Parathyroid Hormone; D015675:Osteocalcin; D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D