title: Determinants of serum 25 hydroxyvitamin D levels in a nationwide cohort of blacks and non-Hispanic whites.
abstract: OBJECTIVE
  To develop algorithms predicting serum 25 hydroxyvitamin D [s25(OH)D] for a large epidemiological study whose subjects come from large geographic areas, are racially diverse and have a wide range in age, skin types, and month of blood sample collection. This will allow a regression calibration approach to determine s25(OH)D levels replacing the more costly method of collection and analysis of blood samples.
  
  
  METHODS
  Questionnaire data from a subsample of 236 non-Hispanic whites (whites) and 209 blacks from the widely dispersed Adventist Health Study-2 (n = 96,000) were used to develop prediction algorithms for races separately and combined. A single blood sample was collected from each subject, at different times throughout the year.
  
  
  RESULTS
  Models with independent variables age, sex, BMI, skin type, UV season, erythemal zone, total dietary vitamin D intake, and sun exposure factor explained 22 and 31% of the variance of s25(OH)D levels in white and black populations, respectively (42% when combined). UV season and erythemal zone determined from measured UV radiation produced models with higher R (2) than season and latitude.
  
  
  CONCLUSIONS
  Combining races with a term for race and using variables with measured UV radiation capture the variance in s25(OH)D levels better than analyzing races separately.
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Loma Linda University, 24785 Stewart St, Loma Linda, CA 92350, USA.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Chan
authors.forename: Karen
authors.initials: K
authors.lastname: Jaceldo-Siegl
authors.forename: Gary E
authors.initials: GE
authors.lastname: Fraser
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000428:Alcohol Drinking; D044383:Black People / Q000706:statistics & numerical data*; D002170:Canada; D015331:Cohort Studies; D019587:Dietary Supplements; D004890:Erythema / Q000209:etiology; D005260:Female; D006801:Humans; D008297:Male; D015999:Multivariate Analysis; D012044:Regression Analysis; D012307:Risk Factors; D012621:Seasons; D012880:Skin Pigmentation / Q000528:radiation effects; D012907:Smoking; D011795:Surveys and Questionnaires; D014466:Ultraviolet Rays / Q000009:adverse effects; D014481:United States; D014807:Vitamin D / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood; D044465:White People / Q000706:statistics & numerical data*; D001741:Black or African American
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D