title: Predictors of 25(OH)D half-life and plasma 25(OH)D concentration in The Gambia and the UK.
abstract: Predictors of 25(OH)D3 half-life were factors associated with vitamin D metabolism, but were different between people in The Gambia and the UK. Country was the strongest predictor of plasma 25(OH)D concentration, probably as a marker of UVB exposure. 25(OH)D3 half-life may be applied as a tool to investigate vitamin D expenditure.
  
  
  BACKGROUND
  The aim of this study was to investigate predictors of 25(OH)D3 half-life and plasma 25(OH)D concentration.
  
  
  METHODS
  Plasma half-life of an oral tracer dose of deuterated-25(OH)D3 was measured in healthy men aged 24-39 years, resident in The Gambia, West Africa (n = 18) and in the UK during the winter (n = 18), countries that differ in calcium intake and vitamin D status. Plasma and urinary markers of vitamin D, calcium, phosphate and bone metabolism, nutrient intakes and anthropometry were measured.
  
  
  RESULTS
  Normally distributed data are presented as mean (SD) and non-normal data as geometric mean (95% CI). Gambian compared to UK men had higher plasma concentrations of 25(OH)D (69 (13) vs. 29 (11) nmol/L; P < 0.0001); 1,25(OH)2D (181 (165, 197) vs. 120 (109, 132) pmol/L; P < 0.01); and parathyroid hormone (PTH) (50 (42, 60) vs. 33 (27, 39); P < 0.0001). There was no difference in 25(OH)D3 half-life (14.7 (3.5) days vs. 15.6 (2.5) days) between countries (P = 0.2). In multivariate analyses, 25(OH)D, 1,25(OH)2D, vitamin D binding protein and albumin-adjusted calcium (Caalb) explained 79% of variance in 25(OH)D3 half-life in Gambians, but no significant predictors were found in UK participants. For the countries combined, Caalb, PTH and plasma phosphate explained 39 % of half-life variability. 1,25(OH)2D, weight, PTH and country explained 81% of variability in 25(OH)D concentration; however, country alone explained 74%.
  
  
  CONCLUSIONS
  Factors known to affect 25(OH)D metabolism predict 25(OH)D3 half-life, but these differed between countries. Country predicted 25(OH)D, probably as a proxy measure for UVB exposure and vitamin D supply. This study supports the use of 25(OH)D half-life to investigate vitamin D metabolism.
authors.affiliation: Elsie Widdowson Laboratory, Medical Research Council Human Nutrition Research, Fulbourn Road, Cambridge, CB1 9NL, UK, kerry.jones@mrc-hnr.cam.ac.uk.
authors.forename: K S
authors.initials: KS
authors.lastname: Jones
authors.forename: S
authors.initials: S
authors.lastname: Assar
authors.forename: D
authors.initials: D
authors.lastname: Vanderschueren
authors.forename: R
authors.initials: R
authors.lastname: Bouillon
authors.forename: A
authors.initials: A
authors.lastname: Prentice
authors.forename: I
authors.initials: I
authors.lastname: Schoenmakers
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000378:metabolism; D002112:Calcifediol / Q000097:blood*; D003903:Deuterium; D004032:Diet / Q000208:ethnology; D005502:Food; D005714:Gambia / Q000208:ethnology; D006207:Half-Life; D006801:Humans; D008297:Male; D010710:Phosphates / Q000378:metabolism; D012307:Risk Factors; D006113:United Kingdom / Q000208:ethnology; D014807:Vitamin D / Q000097:blood*; D055815:Young Adult
chemical_list: D015415:Biomarkers; D010710:Phosphates; D014807:Vitamin D; D003903:Deuterium; D002112:Calcifediol