title: Selenium and mercury in the Brazilian Amazon: opposing influences on age-related cataracts.
abstract: BACKGROUND
  Age-related cataracts (ARCs) are an important cause of blindness in developing countries. Although antioxidants may be part of the body's defense to prevent ARC, environmental contaminants may contribute to cataractogenesis. In fish-eating populations of the lower Tapajós region, elevated exposure to mercury (Hg) has been reported, and blood levels of selenium (Se) range from normal to very high (> 1,000 microg/L).
  
  
  OBJECTIVE
  We examined ARCs in relation to these elements among adults (> or = 40 years of age) from 12 riverside communities.
  
  
  METHODS
  Participants (n = 211) provided blood samples and underwent an extensive ocular examination. Inductively coupled plasma mass spectrometry was used to assess Hg and Se in blood and plasma.
  
  
  RESULTS
  One-third (n = 69; 32.7%) of the participants had ARC. Lower plasma Se (P-Se; < 25th percentile, 110 microg/L) and higher blood Hg (B-Hg; > or = 25th percentile, 25 microg/L) were associated with a higher prevalence odds ratio (POR) of ARC [adjusted POR (95% confidence interval), 2.69 (1.11-6.56) and 4.45 (1.43-13.83), respectively]. Among participants with high P-Se, we observed a positive but nonsignificant association with high B-Hg exposure, whereas among those with low B-Hg, we observed no association for P-Se. However, compared with the optimum situation (high P-Se, low B-Hg), the POR for those with low P-Se and high B-Hg was 16.4 (3.0-87.9). This finding suggests a synergistic effect.
  
  
  CONCLUSIONS
  Our results suggest that persons in this population with elevated Hg, the cataractogenic effects of Hg may be offset by Se. Because of the relatively small sample size and possible confounding by other dietary nutrients, additional studies with sufficient power to assess multiple nutrient and toxic interactions are required to confirm these findings.
authors: Centre de recherche interdisciplinaire sur la biologie, la santé, la société et l'environnement, Université du Ouébec a Montréal, Montréal, Canada. melanie.lemire@crchuq.ulaval.ca
authors: Mélanie
authors: M
authors: Lemire
authors: Myriam
authors: M
authors: Fillion
authors: Benoît
authors: B
authors: Frenette
authors: Annie
authors: A
authors: Mayer
authors: Aline
authors: A
authors: Philibert
authors: Carlos José Sousa
authors: CJ
authors: Passos
authors: Jean Rémy Davée
authors: JR
authors: Guimarães
authors: Fernando Júnior
authors: FJ
authors: Barbosa
authors: Donna
authors: D
authors: Mergler
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000975:Antioxidants / Q000378:metabolism; D001938:Brazil / Q000453:epidemiology; D002386:Cataract / Q000453:epidemiology*; D004032:Diet / Q000706:statistics & numerical data*; D004781:Environmental Exposure / Q000032:analysis / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008767:Methylmercury Compounds / Q000097:blood* / Q000633:toxicity; D008875:Middle Aged; D015999:Multivariate Analysis; D016017:Odds Ratio; D012643:Selenium / Q000097:blood*; D014874:Water Pollutants, Chemical / Q000097:blood* / Q000633:toxicity
chemical_list: D000975:Antioxidants; D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D012643:Selenium