title: Ethnic and socioeconomic differences in variability in nutritional biomarkers.
abstract: BACKGROUND
  Several studies have reported ethnic, education, and income differentials in concentrations of selected nutritional biomarkers in the US population. Although biomarker measurements are not subject to biased self-reports, biologic variability due to individual characteristics and behaviors related to dietary exposures contributes to within-subject variability and measurement error.
  
  
  OBJECTIVE
  We aimed to establish whether the magnitude of components of variance for nutritional biomarkers also differs in these high-risk groups.
  
  
  METHODS
  We used data from 2 replicate measurements of serum concentrations of vitamins A, C, D, and E; folate; carotenoids; ferritin; and selenium in the third National Health and Nutrition Examination Survey second examination subsample (n = 948) to examine the within-subject and between-subject components of variance. We used multivariate regression methods with log-transformed analyte concentrations as outcomes to estimate the ratios of the within-subject to between-subject components of variance by categories of ethnicity, income, and education.
  
  
  RESULTS
  In non-Hispanic blacks, the within-subject to between-subject variance ratio for beta-cryptoxanthin concentration was higher (0.23; 95% CI: 0.17, 0.29) relative to non-Hispanic whites (0.13; 0.11, 0.16) and Mexican Americans (0.11; 0.07, 0.14), and the lutein + zeaxanthin ratio was higher (0.29; 0.21, 0.38) relative to Mexican Americans (0.15; 0.10, 0.19). Higher income was associated with larger within-subject to between-subject variance ratios for serum vitamin C and red blood cell folate concentrations but smaller ratios for serum vitamin A. Overall, there were few consistent up- or down-trends in the direction of covariate-adjusted variability by ethnicity, income, or education.
  
  
  CONCLUSIONS
  Population groups at high risk of adverse nutritional profiles did not have larger variance ratios for most of the examined biomarkers.
authors.affiliation: Department of Family, Nutrition, and Exercise Sciences, Queens College of the City University of New York, Flushing, NY 11367, USA. ashima.kant@qc.cuny.edu
authors.forename: Ashima K
authors.initials: AK
authors.lastname: Kant
authors.forename: Barry I
authors.initials: BI
authors.lastname: Graubard
mesh_terms: D001741:Black or African American / Q000706:statistics & numerical data; D001205:Ascorbic Acid / Q000097:blood; D015415:Biomarkers / Q000097:blood; D002338:Carotenoids / Q000097:blood; D004522:Educational Status; D005006:Ethnicity / Q000706:statistics & numerical data*; D005260:Female; D005293:Ferritins / Q000097:blood; D005492:Folic Acid / Q000097:blood; D006306:Health Surveys; D006801:Humans; D008297:Male; D017058:Mexican Americans / Q000706:statistics & numerical data; D018977:Micronutrients / Q000097:blood*; D008875:Middle Aged; D015999:Multivariate Analysis; D009752:Nutritional Status; D011203:Poverty; D012044:Regression Analysis; D012643:Selenium / Q000097:blood; D012959:Socioeconomic Factors; D014481:United States; D014801:Vitamin A / Q000097:blood; D014807:Vitamin D / Q000097:blood; D014810:Vitamin E / Q000097:blood; D014815:Vitamins / Q000097:blood*; D044465:White People / Q000706:statistics & numerical data
chemical_list: D015415:Biomarkers; D018977:Micronutrients; D014815:Vitamins; D014801:Vitamin A; D014807:Vitamin D; D014810:Vitamin E; D002338:Carotenoids; D005293:Ferritins; D005492:Folic Acid; D012643:Selenium; D001205:Ascorbic Acid