Selenium and mercury in the Brazilian Amazon: opposing influences on age-related cataracts.
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.
Lemire
Mélanie
M
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
Fillion
Myriam
M
Frenette
Benoît
B
Mayer
Annie
A
Philibert
Aline
A
Passos
Carlos José Sousa
CJ
Guimarães
Jean Rémy Davée
JR
Barbosa
Fernando Júnior
FJ
Mergler
Donna
D
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
D000975:Antioxidants; D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D012643:Selenium