However,theresearchersalsofoundthattheamountofmercuryinawoman'sbodyrosewiththeamountoffishshehadconsumed--andthatchildrenexposedtomoremercuryperformedworseonthesetests.Basedonthefindings,theysay,it'spossiblefishcouldhaveevengreaterbrainbenefitsforbabiesifmothers-to-beconsumedseafoodwithlowermercurylevels.
"Recommendationsforfishconsumptionduringpregnancyshouldtakeintoaccountthenutritionalbenefitsoffishaswellasthepotentialharmsfrommercuryexposure,"Dr.EmilyOkenofHarvardMedicalSchoolinBostonandhercolleagueswriteintheMay15issueoftheAmericanJournalofEpidemiology.
Advisoriesonmercurycontaminationofcertaintypesoflarge,long-livedfish--includingtunaandswordfish--haveraisedconcernsaboutseafoodconsumptionduringpregnancy,Okenandherteamnote.Ontheotherhand,fisharealsothechiefdietarysourceofomega-3fattyacids,substanceskeytoearlybraindevelopment,theyadd.
Tobetterunderstandtherisksandbenefitsoffishconsumption,Okenandherteamsurveyed341mothersabouttheirintakeoffishduringthesecondtrimesterofpregnancy,andthenhadtheirchildrencompleteabatteryoftestsofcognitivefunctionat3yearsofage.
Onaverage,womenreportedeating1.5servingsoffisheachweekwhiletheywerepregnant.Theamountofmercurythewomenhadintheirredbloodcellswasdirectlyrelatedtotheamountoffishtheyate.Children'stestscoresrosewiththeamountoffishtheirmothershadconsumed,butthosewhosemothershadmoremercuryintheirbodiesperformedlesswellonthetests.
Accountingfortheeffectsofmercuryexposurestrengthenedtheeffectoffishintake,andviceversa,theresearchersfound.Benefitswerestrongestforchildrenwhosemothersatemorethantwoservingsaweek.
"Ourfindingthatthebenefitoffishintakeisstrengthenedwithadjustmentformercurylevelssuggeststhatifmercurycontaminationwerenotpresent,thecognitivebenefitsoffishwouldbegreater,"Okenandherteamexplain."Maternalconsumptionoffishlowerinmercuryandreducedenvironmentalmercurycontaminationwouldallowforstrongerbenefitsoffishintake."
SOURCE:AmericanJournalofEpidemiology,May15,2008.
