title: Lack of association between fingernail selenium and thyroid cancer risk: a case-control study in French Polynesia.
abstract: BACKGROUND
  Numerous studies have suggested that selenium deficiency may be associated with an increased risk for several types of cancer, but few have focused on thyroid cancer.
  
  
  METHODS
  We examined the association between post-diagnostic fingernail selenium levels and differentiated thyroid cancer risk in a French Polynesian matched case-control study. Conditional logistic regression models were used to estimate odds ratios and 95% confidence intervals.
  
  
  RESULTS
  The median selenium concentration among controls was 0.76 μg/g. Significantly, we found no association between fingernail selenium levels and thyroid cancer risk after conditioning on year of birth and sex and additionally adjusting for date of birth (highest versus lowest quartile: odds-ratio=1.12, 95% confidence interval: 0.66-1.90; p-trend=0.30). After additional adjustment for other covariates, this association remained non-significant (p-trend=0.60). When restricting the analysis to thyroid cancer of 10 mm or more, selenium in nails was non-significantly positively linked to thyroid cancer risk (p-trend=0.09). Although no significant interaction was evidenced between iodine in nails and selenium in nails effect (p=0.70), a non-significant (p-trend =0.10) positive association between selenium and thyroid cancer risk was seen in patients with less than 3 ppm of iodine in nails. The highest fingernail selenium concentration in French Polynesia was in the Marquises Islands (M=0.87 μg/g) and in the Tuamotu-Gambier Archipelago (M=0.86 μg/g).
  
  
  CONCLUSIONS
  Our results do not support, among individuals with sufficient levels of selenium, that greater long-term exposure to selenium may reduce thyroid cancer risk. Because these findings are based on post-diagnostic measures, studies with prediagnostic selenium are needed for corroboration.
authors.affiliation: Radiation Epidemiology Group, Centre for Research in Epidemiology and Population Health (CESP), UMR 1018 Inserm, France E-mail Florent.DEVATHAIRE@gustaveroussy.fr.
authors.forename: Yan
authors.initials: Y
authors.lastname: Ren
authors.forename: Cari Meinhold
authors.initials: CM
authors.lastname: Kitahara
authors.forename: Amy
authors.initials: A
authors.lastname: Berrington de Gonzalez
authors.forename: Enora
authors.initials: E
authors.lastname: Clero
authors.forename: Pauline
authors.initials: P
authors.lastname: Brindel
authors.forename: Stephane
authors.initials: S
authors.lastname: Maillard
authors.forename: Suzanne
authors.initials: S
authors.lastname: Cote
authors.forename: Eric
authors.initials: E
authors.lastname: Dewailly
authors.forename: Frederique
authors.initials: F
authors.lastname: Rachedi
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Boissin
authors.forename: Joseph
authors.initials: J
authors.lastname: Sebbag
authors.forename: Larrys
authors.initials: L
authors.lastname: Shan
authors.forename: Frederique
authors.initials: F
authors.lastname: Bost-Bezeaud
authors.forename: Patrick
authors.initials: P
authors.lastname: Petitdidier
authors.forename: Constance
authors.initials: C
authors.lastname: Xhaard
authors.forename: Carole
authors.initials: C
authors.lastname: Rubino
authors.forename: Florent
authors.initials: F
authors.lastname: de Vathaire
mesh_terms: D016022:Case-Control Studies; D016001:Confidence Intervals; D004198:Disease Susceptibility; D005260:Female; D006801:Humans; D007455:Iodine / Q000737:chemistry; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009262:Nails / Q000378:metabolism*; D016017:Odds Ratio; D011114:Polynesia; D012306:Risk; D012643:Selenium / Q000378:metabolism*; D013961:Thyroid Gland / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000209:etiology* / Q000378:metabolism*
chemical_list: D007455:Iodine; D012643:Selenium