Ethnic and socioeconomic differences in variability in nutritional biomarkers.
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.
Kant
Ashima K
AK
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
Graubard
Barry I
BI
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
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