title: Toenail and plasma levels as biomarkers of selenium exposure.
abstract: OBJECTIVE
  Both blood and toenail selenium are used to assess selenium exposure in epidemiologic studies. Little is known about the relationship of these biomarkers with each other or about whether there are differences in the relationships of these biomarkers with diet, supplement use, or participant characteristics.
  
  
  METHODS
  Data are from 220 participants in a large cohort study of supplement use and cancer risk. Measures of selenium exposure included supplement use (current and 10-year) from a self-administered questionnaire, an inventory of currently used supplements (multivitamins and single supplements), dietary intake from a food frequency questionnaire (FFQ), and selenium concentration in toenails and plasma.
  
  
  RESULTS
  Plasma and toenail selenium concentrations were significantly correlated (r=.56 [95% confidence interval: .46, .64]). Supplemental selenium was the strongest predictor of both selenium biomarkers, and these associations were slightly stronger when based on the supplement inventory and 10-year self-reported use compared to current self-reported use. Correlations of current and 10-year questionnaire dose and inventory dose with toenail selenium were .26, .36, and .33; for plasma selenium, these were .27, .36, and .36. Neither dietary selenium nor any participant characteristics, except smoking, was related to either biomarker. Current smokers had lower toenail, but not plasma, selenium levels compared to nonsmokers (.89 versus 1.03 microg/g, p = .03); however, the difference was not significant after control for supplement use (p = .09).
  
  
  CONCLUSIONS
  Both toenail and plasma selenium levels similarly reflect selenium intake exposure. There do not appear to be independent associations of toenail or plasma selenium with FFQ-derived selenium intakes, health-related behaviors, or demographic characteristics.
authors.affiliation: Department of Nutrition, and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, USA. jessie.satia@amgen.com
authors.forename: Jessie A
authors.initials: JA
authors.lastname: Satia
authors.forename: Irena B
authors.initials: IB
authors.lastname: King
authors.forename: J Steven
authors.initials: JS
authors.lastname: Morris
authors.forename: Kayla
authors.initials: K
authors.lastname: Stratton
authors.forename: Emily
authors.initials: E
authors.lastname: White
mesh_terms: D015415:Biomarkers; D015331:Cohort Studies; D004032:Diet / Q000009:adverse effects; D019587:Dietary Supplements / Q000009:adverse effects / Q000032:analysis*; D004781:Environmental Exposure / Q000032:analysis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009262:Nails / Q000737:chemistry*; D009369:Neoplasms / Q000139:chemically induced; D018570:Risk Assessment; D012643:Selenium / Q000032:analysis* / Q000633:toxicity; D011795:Surveys and Questionnaires; D014861:Washington
chemical_list: D015415:Biomarkers; D012643:Selenium