title: ASSOCIATION BETWEEN 25-HYDROXYVITAMIN D AND INTACT PARATHYROID HORMONE LEVELS ACROSS LATITUDE AMONG ADULTS WITH AFRICAN ANCESTRY.
abstract: OBJECTIVE
  To compare levels of 25-hydroxyvitamin D (25[OH]D) associated with a plateauing of intact parathyroid (iPTH) across latitudes among adults with African ancestry.
  
  
  METHODS
  This study included approximately 500 adults of African ancestry ages 25 to 45 years living in 4 sites: Chicago, Illinois (41°N), Jamaica (17°N), Ghana (6°N), and South Africa (34°S). Multivariate linear regression models, a nonlinear logistic growth curve model, and piecewise linear models with a single knot were fitted to estimate the 25[OH]D level associated with a plateauing of iPTH with adjustment for covariates. Goodness of fit was compared using computer intensive permutation tests.
  
  
  RESULTS
  Mean age was 34.7 (SD 6.2) years, and 46.5% were male. Within each site, the percentage of participants with an iPTH level ≥65 pg/mL was higher among females versus males and was most frequent among South African females (17.1%) and lowest among Jamaican males (0.6%). Goodness of fit tests supported linear regression as the preferred model for the association between iPTH and 25[OH]D in the 4 sites with no 25[OH]D level associated with iPTH plateauing in any site. The slope of the association between 25[OH]D and iPTH differed by latitude; it was strongest in the U.S. (β = -0.81; 95% confidence interval [CI] = -1.03, -0.59), and weakest in Jamaica (β = -0.45; 95% CI -0.71, -0.18) with covariate adjustment, but differences in slopes were small.
  
  
  CONCLUSIONS
  The association between 25[OH]D and iPTH appears linear among adults with African ancestry regardless of latitude within a range of 25[OH]D levels between 10 and 60 ng/mL.
  
  
  BACKGROUND
  BMI = body mass index CI = confidence interval eGFR = estimated glomerular filtration rate iPTH = intact parathryoid hormone 25[OH]D = 25-hydroxyvitamin D.
authors.forename: Holly
authors.initials: H
authors.lastname: Kramer
authors.forename: Pauline
authors.initials: P
authors.lastname: Camacho
authors.forename: John
authors.initials: J
authors.lastname: Aloia
authors.forename: Amy
authors.initials: A
authors.lastname: Luke
authors.forename: Pascal
authors.initials: P
authors.lastname: Bovet
authors.forename: Jacob Plange
authors.initials: JP
authors.lastname: Rhule
authors.forename: Terrence
authors.initials: T
authors.lastname: Forrester
authors.forename: Vickie
authors.initials: V
authors.lastname: Lambert
authors.forename: Regina
authors.initials: R
authors.lastname: Harders
authors.forename: Lara
authors.initials: L
authors.lastname: Dugas
authors.forename: Richard
authors.initials: R
authors.lastname: Cooper
authors.forename: Ramon
authors.initials: R
authors.lastname: Durazo-Arvizu
mesh_terms: D000328:Adult; D044383:Black People / Q000706:statistics & numerical data; D002641:Chicago; D005260:Female; D005869:Ghana; D006801:Humans; D007087:Illinois; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D013019:South Africa; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000208:ethnology; D001741:Black or African American
chemical_list: D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D