American Journal of Epidemiology Advance Access originally published online on June 12, 2008
American Journal of Epidemiology 2008 168(2):236; doi:10.1093/aje/kwn172
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LETTERS TO THE EDITOR |
RE: "MATERNAL FISH INTAKE DURING PREGNANCY, BLOOD MERCURY LEVELS, AND CHILD COGNITION AT AGE 3 YEARS IN A US COHORT"
Groth Consulting Services, Pelham, NY 10803-1702
(e-mail: nedgroth{at}cs.com)
Oken et al. (1) report that methylmercury exposure associated with maternal fish consumption at or above two meals per week adversely affects cognitive development measured at age 3 years, confirming their earlier report of similar effects at age 6 months (2). Their latest results add weight to the possibility that no level of methylmercury exposure is without appreciable risk to the developing brain. Although their study was limited in scope, it reminds me of work done a generation ago by Needleman et al. (3), who first demonstrated the adverse effects of lead on learning ability and behavior in children with exposures in the "normal" range. If the results by Oken et al. are confirmed independently, they may signal the need for a paradigm shift in our approach to methylmercury risk management, as the study by Needleman et al. did for lead.
The fact that fish consumption during pregnancy also benefits cognitive development, with positive effects roughly comparable in magnitude to the negative effects of methylmercury, as Oken et al. also observed, complicates risk management and risk communication on this subject. Oken et al. recommend that pregnant women should continue to eat fish but urge them to be aware of the risks and to choose low-mercury fish.
That is sound general advice, but it offers no specific guidance on such key questions as the following: What is "low-mercury" fish and how much fish is it safe to consume while pregnant?
The US Food and Drug Administration has published data on mercury levels in fish and shellfish varieties (4); however, to be useful for consumers, that information needs to be interpreted and publicized. Listed below are some fish and shellfish that, according to Food and Drug Administration data, each contain less than 10 µg of methylmercury in a 6-ounce (170-g) serving. A 60-kg woman has a methylmercury reference dose of 42 µg/week (5). She could therefore eat up to four servings per week (or twice the intake that defined "high" fish eaters in the study population of Oken et al.) of any of the listed items, without exceeding the safe methylmercury dose as specified by the US Environmental Protection Agency.
According to this definition, low-mercury fish and shellfish include shrimp, clams, salmon, tilapia, pollock, sole, flounder, catfish, whiting, oysters, sardines, haddock, anchovies, herring, and scallops. The first eight choices listed are among the most heavily consumed seafood items in the US diet (6), while salmon, oysters, sardines, anchovies, and herring are also excellent sources of beneficial omega-3 fatty acids (7).
No variety of canned tuna is on the list. Although canned tuna was the most frequently consumed fish product among the subjects in the study reported in 2003 by Oken et al. (8), it does not meet the criteria stated above for "low-mercury" fish. One serving (170 g) of canned "light" tuna provides, on average, about 20 µg of methylmercury, while a similar amount (170 g) of canned "white" (albacore) tuna contains 60 µg of methylmercury (4).
Although the results of Oken et al. must be considered tentative until reproduced by others, it would be prudent public-health policy to help women of childbearing age make sound seafood choices by expanding current government and other expert advisories to include more detailed information about low-mercury fish and shellfish varieties.
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ACKNOWLEDGMENTS |
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Conflict of interest: none declared.
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NOTES |
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Editor's note: In accordance with Journal policy, Oken et al. were asked whether they wanted to respond to this letter, but they chose not to do so.
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References |
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 TOP References |
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- Oken E, Radesky JS, Wright RO, et al. Maternal fish intake during pregnancy, blood mercury levels, and child cognition at age 3 years in a US cohort. Am J Epidemiol (2008) 167:1171–81.
[Abstract/Free Full Text] - Oken E, Wright RO, Kleinman KP, et al. Maternal fish consumption, hair mercury, and infant cognition in a US cohort. Environ Health Perspect (2005) 113:1376–80.[Web of Science][Medline]
- Needleman HL, Gunnoe C, Leviton A. Deficits in psychologic and classroom performance of children with elevated dentine lead levels. N Engl J Med (1979) 300:689–95.[Abstract]
- Mercury levels in commercial fish and shellfish. Rockville, MD: US Food and Drug Administration, 2006. (http://www.cfsan.fda.gov/
frf/sea-mehg.html). - Rice DC, Schoeny R, Mahaffey K. Methods and rationale for derivation of a reference dose for methylmercury by the US EPA. Risk Anal (2003) 23:107–15.[CrossRef][Web of Science][Medline]
- Institute of Medicine. Seafood choices: balancing benefits and risks. (2006) Washington, DC: National Academy Press.
- Mozaffarian D, Rimm EB. Fish intake, contaminants and human health. Evaluating the risks and the benefits. JAMA (2006) 296:1885–99.
[Abstract/Free Full Text] - Oken E, Kleinman KP, Berland WE, et al. Decline in fish consumption among pregnant women after a national mercury advisory. Obstet Gynecol (2003) 102:346–51.[CrossRef][Web of Science][Medline]
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