Lactose Intolerance in InfantsWord格式文档下载.docx

Lactose Intolerance in InfantsWord格式文档下载.docx

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2008年06月12日21:

46:

07Thursday 

【摘要】 

TheAmericanAcademyofPediatricsCommitteeonNutritionpresentsanupdatedreviewoflactoseintoleranceininfants,children,andadolescents.Differencesbetweenprimary,secondary,congenital,anddevelopmentallactasedeficiencythatmayresultinlactoseintolerancearediscussed.Childrenwithsuspectedlactoseintolerancecanbeassessedclinicallybydietarylactoseeliminationorbytestsincludingnoninvasivehydrogenbreathtestingorinvasiveintestinalbiopsydeterminationoflactase（andotherdisaccharidase）concentrations.Treatmentconsistsofuseoflactase-treateddairyproductsororallactasesupplementation,limitationoflactose-containingfoods,ordairyelimination.TheAmericanAcademyofPediatricssupportsuseofdairyfoodsasanimportantsourceofcalciumforbonemineralhealthandofothernutrientsthatfacilitategrowthinchildrenandadolescents.Ifdairyproductsareeliminated,otherdietarysourcesofcalciumorcalciumsupplementsneedtobeprovided.

【关键词】 

abdominalpainbreathtestscalciumdietarydairyproductsdiarrheaflatulencelactasemalabsorptionpediatric

INTRODUCTION

Significantchangesinourknowledgeandapproachtowardlactoseintolerancehaveoccurredoverthepastquartercentury,sincethefirststatementonlactoseintolerancewaspublishedbytheAmericanAcademyofPediatricsCommitteeonNutrition.1Lactoseingestionincertainsusceptibleindividualscancauseabdominalsymptomsthatarevariableandcanbetreatedwithdietaryrestrictionorenzymereplacement,dependingontheamountoflactoseconsumedandthedegreeoflactasedeficiency.Pediatriciansandotherpediatriccareprovidersshouldmaintainawarenessofthebenefitsandcontroversiesrelatedtotheconsumptionofdietarymilkproductsandmilk-basedinfantformula.Thelactosecontentofmilkofteninfluences,correctlyornot,theultimatedecisionabouttheuseorcontinuationofmilkinthediet.Milkanddairy-productavoidancehasanegativeeffectoncalciumandvitaminDintakeininfants,children,andadolescents.Othernutrientssuchasproteinmakedairyproductsanimportantsourceofnutritionforgrowingchildren.Thisrevisedstatementwillupdatetheinitialstatementof1978whileincorporatingchangesfromthe1990supplement2andcurrentstate-of-the-artrelatingtolactoseintolerance.Recommendationsregardingdietarycalciumhavebeenupdatedrecently.3

Lactose,adisaccharidethatcomprisesthemonosaccharidesglucoseandgalactose,istheprimarycarbohydratefoundexclusivelyinmammalianmilk.Absorptionoflactoserequireslactaseactivityinthesmallintestinalbrushbordertosplitthebondlinkingthe2monosaccharides.A-galactosidasetermed"

lactase-phlorizinhydrolase"

（lactase）accountsformostofthelactaseactivityintheintestinalmucosa.4Lactaseisfoundinthesmallintestineandlocalizedtothetipsofthevilli,afactorofclinicalimportancewhenconsideringtheeffectofdiarrhealillnessontheabilitytotoleratemilk.

Milkintolerancemaybeattributedtoeitherthelactoseortheproteincontent.Lactoseintolerancecanoccuramonginfantsandyoungchildrenwithacutediarrhealdisease,althoughtheclinicalsignificanceofthisislimitedexceptinmoreseverelyaffectedchildren.Symptomsoflactoseintolerancearerelativelycommonamongolderchildrenandadolescents;

however,associatedintestinalinjuryisinfrequentlyseen.Lactoseintoleranceisadistinctentityfromcowmilk–proteinsensitivity,whichinvolvestheimmunesystemandcausesvaryingdegreesofinjurytotheintestinalmucosalsurface.Cowmilk–proteinintoleranceisreportedin2%to5%ofinfantswithinthefirst1to3monthsoflife,typicallyresolvesby1yearofage,andisnotthesubjectofthisstatement.5,6

DEFINITIONS

Followingaredefinitionsoftermsusedintheremainderofthisstatement:

Lactoseintoleranceisaclinicalsyndromeof1ormoreofthefollowing:

abdominalpain,diarrhea,nausea,flatulence,and/orbloatingaftertheingestionoflactoseorlactose-containingfoodsubstances.Theamountoflactosethatwillcausesymptomsvariesfromindividualtoindividual,dependingontheamountoflactoseconsumed,thedegreeoflactasedeficiency,andtheformoffoodsubstanceinwhichthelactoseisingested.

Lactosemalabsorptionisthephysiologicproblemthatmanifestsaslactoseintoleranceandisattributabletoanimbalancebetweentheamountofingestedlactoseandthecapacityforlactasetohydrolyzethedisaccharide.

Primarylactasedeficiencyisattributabletorelativeorabsoluteabsenceoflactasethatdevelopsinchildhoodatvariousagesindifferentracialgroupsandisthemostcommoncauseoflactosemalabsorptionandlactoseintolerance.Primarylactasedeficiencyisalsoreferredtoasadult-typehypolactasia,lactasenonpersistence,orhereditarylactasedeficiency.

Secondarylactasedeficiencyislactasedeficiencythatresultsfromsmallbowelinjury,suchasacutegastroenteritis,persistentdiarrhea,smallbowelovergrowth,cancerchemotherapy,orothercausesofinjurytothesmallintestinalmucosa,andcanpresentatanyagebutismorecommonininfancy.

Congenitallactasedeficiencyisextremelyrare;

teleologically,infantswithcongenitallactasedeficiencywouldnotbeexpectedtosurvivebeforethe20thcentury,whennoreadilyaccessibleandnutritionallyadequatelactose-freehumanmilksubstitutewasavailable.

Developmentallactasedeficiencyisnowdefinedastherelativelactasedeficiencyobservedamongpreterminfantsoflessthan34weeks’gestation.

PrimaryLactaseDeficiency

Approximately70%oftheworld’spopulationhasprimarylactasedeficiency.7,8Thepercentagevariesaccordingtoethnicityandisrelatedtotheuseofdairyproductsinthediet,resultingingeneticselectionofindividualswiththeabilitytodigestlactose（Table1）.Inpopulationswithapredominanceofdairyfoodsinthediet,particularlynorthernEuropeanpeople,asfewas2%ofthepopulationhasprimarylactasedeficiency.Incontrast,theprevalenceofprimarylactasedeficiencyis50%to80%inHispanicpeople,60%to80%inblackandAshkenaziJewishpeople,andalmost100%inAsianandAmericanIndianpeople.9–11Theageofonsetanditsprevalencedifferamongvariouspopulations.Approximately20%ofHispanic,Asian,andblackchildrenyoungerthan5yearsofagehaveevidenceoflactasedeficiencyandlactosemalabsorption,12whereaswhitechildrentypicallydonotdevelopsymptomsoflactoseintoleranceuntilafter4or5yearsofage.Recentmolecularstudiesoflactase-phlorizinhydrolase（lactase）havecorrelatedthegeneticpolymorphismofmessengerRNAexpressionwithpersistenceoflactaseactivity,demonstratingearlyloss（at1–2yearsofage）ofmessengerRNAexpressionandenzymeactivityinThaichildrenandlate（10–20yearsofage）lossofactivityinFinnishchildren.11,13Theclinicalrelevanceoftheseobservationsisthatchildrenwithclinicalsignsoflactoseintoleranceatanearlieragethanistypicalforaspecificethnicgroupmaywarrantanevaluationforanunderlyingcause,becauseprimarylactasedeficiencywouldotherwisebeunusualatsuchayoungage.Althoughprimarylactasedeficiencymaypresentwitharelativelyacuteonsetofmilkintolerance,itsonsettypicallyissubtleandprogressiveovermanyyears.Mostlactase-deficientindividualsexperienceonsetofsymptomsinlateadolescenceandadulthood.

Reportsthatfocusonclinicalsymptomsoflactasedeficiencyarepronetosubjectivity,confoundingclinicaldiagnosis.Forinstance,whenlactase-deficientadultsweregiven2glassesofmilkor2glassesoflactose-hydrolyzedmilkperdayinadouble-blind,crossoverstudy,nostatisticaldifferencesinsymptomsoflactoseintolerancewerefoundregardlessofwhethertheindividualdescribedhimselforherselfaslactoseintolerant.14Evenlactose-intolerantadultsmayfindthat1glassofmilkorascoopoficecreamistolerated,whereasanadditionalglassofmilkorothermilkproductmayproducesymptoms.Becauseofthevariationofdairyintakeineachindividual’sdietandintheamountoflactosecontainedindifferentproducts,symptomsmayvaryandbemodifiedbydietandbymilk-containingfoods（see"

Management"

）.Forthesereasons,dietaryhistoryisanunreliablemeanstoconfirmorexcludethediagnosisoflactoseintolerance.

SecondaryLactaseDeficiency

Secondarylactasedeficiencyimpliesthatanunderlyingpathophysiologicconditionisresponsibleforthelactasedeficiencyandsubsequentlactosemalabsorption.Etiologiesincludeacuteinfection（eg,rotavirus）causingsmallintestinalinjurywithlossofthelactase-containingepithelialcellsfromthetipsofthevilli.Theimmatureepithelialcellsthatreplacetheseareoftenlactasedeficient,leadingtosecondarylactosedeficiencyandlactosemalabsorption,althoughseveralreportsindicatethatlactosemalabsorptioninmostchildrenwithacutegastroenteritisisnotclinicallyimportant.15Severalrecentstudiesandameta-analysisfoundthatchildrenwithrotaviral（andotherinfectious）diarrhealillnesseswhohavenooronlymilddehydrationcansafelycontinuehumanmilkorstandard（lactose-containing）formulawithoutanysignificanteffectonoutcome,includinghydrationstatus,nutritionalstatus,durationofillness,orsuccessoftherapy.16–18However,intheat-riskinfant（eg,youngerthan3monthsormalnourished）whodevelopsinfectiousdiarrhea,lactoseintolerancemaybeasignificantfactorthatwillinfluencetheevolutionoftheillness.