No significant associations between breastfeeding practices and overweight in 8-year-old children

Acta Paediatrica. 2019;00:1–6. wileyonlinelibrary.com/journal/apa |₁

Received:22November2018 

|

|

R E G U L A R A R T I C L E

No significant associations between breastfeeding practices and overweight in 8‐year‐old children

Asborg A. Bjertnæs

 | Jacob H. Grundt

 | Hilde M. Donkor

 | Petur B. Juliusson

 | Tore Wentzel‐Larsen

 | Arild Vaktskjold

 | Trond Markestad

 | Mads N. Holten‐Andersen

Abbreviations:BMI,bodymassindex;WHO,WorldHealthOrganization.

1DepartmentofPaediatrics,Innlandet HospitalTrust,Lillehammer,Norway

2DepartmentofClinicalMedicine,University ofOslo,Norway

3DepartmentofPaediatrics,OsloUniversity Hospital,Oslo,Norway

4DepartmentofHealth

Registries,NorwegianInstituteofPublic Health,Norway

5DepartmentofClinicalScience,University ofBergen,Bergen,Norway

6DepartmentofPaediatrics,Haukeland UniversityHospital,Bergen,Norway

7NorwegianCentreforViolenceand TraumaticStressStudies,Oslo,Norway

8RegionalCentreforChildandAdolescent MentalHealth,EasternandSouthern Norway,Oslo,Norway

9DepartmentofResearch,Innlandet HospitalTrust,Brumunddal,Norway

10DepartmentofPublicHealth

Science,InlandNorwayUniversity,Elverum, Norway

Correspondence

AsborgA.Bjertnæs,Departmentof Paediatrics,InnlandetHospitalTrust, Lillehammer,Norway.

Email:asborg.aanstad.bjertnaes@sykehuset- innlandet.no

Funding information

Thisstudywassupportedbyunrestricted grantsfromtheInnlandetHospitalTrust.

Thefundingsourcedidnotplayanyrole inthedesignandimplementationofthe study;collection,management,analysisor interpretationofthedataandpreparation, revieworapprovalofthemanuscript.

Abstract

Aim: Theaimwastoexamineifbreastfeedingpracticeswereassociatedwithbody massindex(BMI)andriskofoverweightorobesityinthirdgrade(8years)ofelemen- taryschool.

Methods: Inaregionalcohort,werelatedBMIz-scoresandpresenceofoverweight orobesityat8yearsofagewitheverbeingbreastfedandwithdurationofexclusive and partial breastfeeding after adjusting for potential confounders. Parents com- pletedquestionnairesonbreastfeedingandsociodemographicandlifestylefactors atschoolentry,andpublichealthnursesmeasuredheightandweight.Fornon-par- ticipants,thenursesanonymouslyreportedthesemeasurementstogetherwithsex andage.

Results: 90%ofparticipantshadbeenbreastfed.Inadjustedanalyses,BMIz-scores werenotsignificantlyrelatedtowhetherornotthechildhadbeenbreastfed(P=.64), ortothedurationofexclusive(P=.80)orpartialbreastfeeding(P=.94).Logisticre- gressionalsoshowednosignificantassociationbetweenbreastfeedingmeasuresand overweightorobesity.

Conclusion: This study on 8-year-old Norwegian children did not support a com- monlyheldnotionthatbreastfeedingreducestheriskofoverweightorobesity.

K E Y W O R D S

BMI z-score,breastfeeding,child,obesity,overweight

ThisisanopenaccessarticleunderthetermsoftheCreativeCommonsAttribution-NonCommercial-NoDerivsLicense,whichpermitsuseanddistributionin anymedium,providedtheoriginalworkisproperlycited,theuseisnon-commercialandnomodificationsoradaptationsaremade.

@2019SykehusetInnlandetHF.Acta PaediatricapublishedbyJohnWiley&SonsLtdonbehalfofFoundationActaPaediatrica

1  | INTRODUCTION

It is widely accepted that overweight or obesity in childhood has a high, negative impact on adult health and well-being in a global perspective.¹ Established risk factors for childhood overweight or obesity include environmental, sociodemographic and behavioural factors.² The World Health Organization (WHO) endorses breast- feedingasameansofpromotingoptimalgrowthinearlyinfancyand limited weight gain later in life.³ The WHO growth standards are basedonchildrenwhoareexclusivelybreastfedforatleast4months accordingtostrictfeedingcriteria.⁴Thisimpliesthatbreastfedchil- drenrepresentthenormintermsofgrowth.⁵

Nordic breastfeeding recommendations state that extended periodsofbothexclusiveandpartialbreastfeedinghaveaprotec- tiveeffectagainstoverweightandobesityinchildhoodandadoles- cence.⁶ThisnotionaccordswithWHOclaimsandissupportedby meta-analysesofobservationalstudies.^7-9However,theBelarusian PROBITstudyandothersmaller,randomizedstudieshavenotshown aprotectiveeffectofbreastfeedingpromotiononoverweightand obesitybeyondachild’ssecondyear.^10,11Theinconsistentresultsof suchstudieschallengetheassumptionofcausalitybetweenbreast- feeding and childhood overweight and obesity.¹² Motivation and abilitytobreastfeedarecommonlyassociatedwithsocio-economic and behavioural factors, and relationships between breastfeeding and childhood overweight and obesity may, therefore, be difficult tointerpret.¹³Indeed,inameta-analysisbyHortaetal⁸,whichin- cludedrandomized,controlledtrialsandobservationalstudies,ad- justmentsforpotentialconfoundersledtoadecreasingprotective effectofbreastfeeding.

CurrentNorwegianguidelinesrecommendexclusivebreastfeed- ingfor6monthsandcontinuedpartialbreastfeedinguntilthechild is at least 12 months old.¹⁴ In a recent large-scale, regional regis- terstudy,74%ofmothersexclusivelybreastfedand17%partially breastfedtheirinfantsat6weeks,andtherespectivefigureswere 19% and 55% at 6 months.¹⁵ Given that breastfeeding is widely adoptedinNorwayandcharacterisedbylargevariationsinextent andduration,ouraimwastoexaminewhetheranybreastfeedingor whetherdurationofexclusiveandpartialbreastfeedingwasassoci- atedwithbodymassindex(BMI)z-scoresandariskofoverweight orobesityat8yearsofageinaregionalcohortafteradjustingfor potentialconfounders.

2  | METHODS

2.1 | Population

Theparentsofallchildrenwhostartedschoolin2007inOppland County, Norway, were invited to participate in the study during the routine school-entry health assessments at 5-6 years of age.

Consenting parents completed a questionnaire on breastfeeding practices, lifestyle factors of the child and family, anthropometric measurementsandsociodemographicdataofthefamilyandhealth of the child. School nurses measured the height and weight of all

eligiblechildreninthirdgradeofelementaryschool(about8yearsof age).Forthechildrenwithparentalconsent,themeasurementswere mergedwithdataobtainedonschoolentry,andlengthandweight atbirthreportedbytheobstetricdepartments.Forchildrenwithout parentalconsent,thenursesanonymouslyreportedsex,currentage, heightandweighttotheresearchers.Opplandisapredominantly ruralcountywithapproximately185000inhabitantslivingin26mu- nicipalities.Twoofthemunicipalitieshavecitiesof25000-30000 inhabitants;therestareruralareaswithtownsofvariablesizesand 44%ofthepopulationlivesinscatteredareas.¹⁶

2.2 | Outcome and adjusting measures

Body mass index standard deviation score (z-score) in third grade wastheprimaryoutcomeandoverweightorobesityvsnotthesec- ondaryoutcome.BMIz-scoreswerebasedonupdatedNorwegian growth reference data,¹⁷ and overweight or obesity were defined accordingtotheInternationalObesityTaskForce.¹⁸

Explanatory variables were obtained before school entry, and includedwhetherthechildhadbeenbreastfedornot,whetherthe childhadbeenexclusivelybreastfedfor<4months,durationofpar- tialbreastfeeding(months)anddurationofexclusivebreastfeeding (months).Theadditionaladjustingvariablesrepresentedfouraddi- tional thematic groups: lifestyle parameters, anthropometric data, sociodemographicfactorsandgeneralhealthofthechild.Lifestyle parametersofthechildandfamilyincluded:proxiesforchildnutri- tion(eatingvegetables<5times/wkvsmoreoftenandeatingfour mainmealsincluding:cerealsorsandwichforbreakfast,sandwiches and fruit for lunch, a hot meal prepared at home for dinner and sandwichesforsupper<5daysperweekvsmoreoften),proxiesfor physicalactivity(alevelofexertiongeneratingheavybreathingor sweating <4 times per week vs more often and daily screen time

>2hoursvsshorter)andparentalsmoking(yes/no).Anthropometric dataincludedweightandlengthofthechildatbirth.Currentparen- tal and sibling heights and weights were reported by the parents.

Sociodemographic factors included: maternal age at delivery, the Key notes

• Bodymassindex(BMI)z-scoreinthethirdgrade(8years ofage)wasnotsignificantlyassociatedwithbreastfeed- ingpractices.

• Therewasnosignificantassociationbetweenduration of breastfeeding in infancy and BMIz-score or over- weight or obesity, indicating no significant dose-re- sponserelationship.

• Inthiscohortwithhighfrequencyofbreastfeeding,we donotsupportpreviousobservationalstudiesofasso- ciationsbetweenbreastfeedingandoverweightinchil- drenfromhigh-incomepopulations.

child’ssex,currentmaritalstatusoftheparents,numberofchildren inthefamily,maternalandpaternaleducation≤12yearsvslonger,≥1 parentoriginatingfromcountriesoutsideEuropeorNorthAmerica ornotandresidencyinruraldistrictsvsthetwocities. Proxy vari- ables for general health of the childincludedprematurevstermbirth, havinghadcariesornot,everhavingbeentreatedwithantibiotics ornot,havingsufferedachronicdiseaseornotandusingasthma medicationbeyond2yearsofageornot.

2.3 | Statistical analysis

Differencesinmeansandproportionsbetweenparticipantsand non-participants were calculated using the Student’st test and Pearson’schi-squaretest.Associationswereinvestigatedbetween each of the breastfeeding variables and BMIz-score and having overweightorobesityornot,respectively,usingunadjustedand adjusted linear and logistic regression analyses Differences in smoking habits and education for mothers that report exclusive breastfeedingmoreorlessthan4monthswerealsoinvestigated usingPearson’schi-squaretest.Alllistedvariablesintheadjusted models were included since previous research has found them tobeassociatedwithoverweightorobesity.^9,19Multicollinearity wasassessedusingvarianceinflationfactor(VIF),andthesignifi- cancelevelwassetto5%.Interactionsbetweendurationofpar- tial breastfeeding and maternal smoking and duration of partial breastfeeding and maternal education were tested in additional models.StatisticalanalyseswerecarriedoutusingSPSSStatistics forWindows,Version23.0.0.2Armonk,NY:IBMCorpandSTATA 15.0software(STATA).

2.4 | Ethics

Signedconsentfromoneparentwasobtainedforeachparticipating child,andtheRegionalCommitteeforMedicalResearchEthicsap- provedthestudy(projectnumber:1.2006.3491).

3  | RESULTS

Consentwasobtainedfromparentsof951(47%)ofthe2012eligi- blechildren.Participatingchildrendidnotdiffersignificantlyfrom non-participants in mean age, height, weight, BMI or in rates of overweightorobesity,buttheproportionofboyswasslightlylower amongtheparticipants(Table1).Oftheparticipatingchildren,21%

hadoverweightorobesityand90%hadbeenexclusivelybreastfed foramean(standarddeviation)durationof4.6(2.6)monthsandpar- tiallybreastfedfor10.7(6.1)months.

Exceptfortheunadjustedlinearregressionanalysisfor<4months ofexclusivebreastfeeding,noneoftheunivariateanalysesdisplayed significant associations between breastfeeding practises and BMI.

Furthermore,wefoundnosignificantadjustedassociationsbetween durationofpartialbreastfeeding(Table2)oranyoftheotherbreast- feedingmeasuresandneitherBMIz-score,norratesofoverweightor obesityinlinearorlogisticregressionanalyses(Table3).Wefounda significantly higher fraction of less educated mothers among those whoreportedexclusivebreastfeeding<4monthsascomparedwith≥4- monthexclusivebreastfeeding(difference0.18[0.07,0.29],P<.001).

Therewerenoindicationsofmulticollinearity(VIFscoreswere≤1.3in multivariableregressionanalyses)or,inadditionalanalyses,significant interactionsbetweendurationofpartialbreastfeedingandmaternal education(P=.61)ormaternalsmoking(P=.52)(datanotshown).

4  | DISCUSSION

Body mass indexz-score or having overweight or obesity in the thirdgrade(atabout8yearsofage)werenotsignificantlyrelated tobeingbreastfedornot,ortothedurationofexclusiveorpartial breastfeeding.

We found indications of an association between being exclu- sively breastfed <4 months in univariate analyses, but not in ad- justedanalysesforneitherlinear,norlogisticregression.Theresult

Total Participants Non‐participants

P‐value*

(n = 2012) (n = 951) (n = 1061)

Boys,n(%) 996(49.5) 440(46.3) 556(52.4) .006

Age(years),mean(SD) 8.3(1.0) 8.26(1.0) 8.3(1.1) .98

Height(cm),mean(SD) 131.6(8.1) 131.78(8.2) 131.3(8.0) .22 Weight(kg),mean(SD) 29.7(7.2) 29.80(7.1) 29.7(7.3) .67 Bodymassindex(kg/

m²),mean(SD) 17.0(2.6) 17.0(2.5) 17.0(2.6) .83

Overweightorobese^a, n(%)

415(20.6) 201(21.1) 214(20.2) .62

Girls 234(23.0) 116(22.7) 118(23.4)

Boys 181(18.2) 85(19.3) 96(17.3)

Abbreviation:SD,standarddeviation.

aBasedonbodymassindex,iso-BMI≥25.

*Chi-squareforcategoricalvariablesandStudent`stestforcontinuousvariables.

TA B L E 1  Characteristicsofthe participantsandnon-participantsofthe study

forthecrudeanalysiscanbeexplainedbyourfindingofanassoci- ationbetweenbreastfeedingandsocio-economy,andisinlinewith earlierresearchshowingthatexclusivebreastfeedingat4monthsis associatedwithsocio-economicfactors.¹³

Our results are in agreement with those of the PROBIT study wherebreastfeedingwasnotfoundtohaveanyprotectiveeffect on overweight and obesity beyond the age of 2 years¹¹ and do notagreewiththefindingsofmostotherobservationalstudiesin TA B L E 2  Unadjustedandadjustedlinearregressionanalyses^a,b

Unadjusted analysis Adjusted analysis

Mean (SD) or % Coef^c 95% CI P‐value Coef^c 95% CI P‐value Breastfeedingpractices

Everbreastfed 90.3 0.209 −0.02,0.44 .075

<4moofexclusivebreastfeeding 28.1 0.230 0.08, 0.37 .003 Exclusivebreastfeeding(months) 4.6(2.6) −0.009 −0.04,0.02 .544

Partialbreastfeeding(months)^b 10.7(6.1) −0.007 −0.02,0.01 .242 0.00 −0.01,0.01 .941 Lifestyleofthechildandfamily

Eatingvegetables<5times/wk 49.9 0.004 −0.13,0.14 .959

Nothavingregularmeals^b,d 29.5 0.040 −0.11,0.19 .569 0.06 −0.11,0.23 .466

Activity<4times/wk^b 47.7 −0.070 −0.20,0.07 .357 −0.05 −0.20,0.11 .555

Screentime>2h/d^b 31.1 0.160 0.01, 0.31 .035 0.03 −0.14,0.19 .774

Maternalsmoking^b 19.1 0.470 0.30, 0.64 <.001 0.34 0.12,0.56 .003

Paternalsmoking^b 21.7 0.220 0.05,0.38 .009 −0.04 −0.25,0.16 .689

Anthropometricdata

Birthlengthz-score 0.07(1.0) 0.104 0.03, 0.18 .004

Birthweightz-score^b −0.11(1.1) 0.170 0.11, 0.23 <.001 0.12 0.06, 0.19 <.001

MaternalBMI^b 24.3(3.8) 0.074 0.06, 0.09 <.001 0.05 0.03, 0.08 <.001

PaternalBMI^b 26.5(3.3) 0.090 0.07, 0.11 <.001 0.06 0.04, 0.09 <.001

MeansiblingBMIz-score^e −0.24(1.2) 0.230 0.16, 0.30 <.001 Sociodemographicfactors

Ageofmotheratdelivery(years) 30.0(4.8) 0.004 −0.01,0.02 .551

Boy^b 46.3 0.173 0.04, 0.31 .013 0.27 0.12, 0.42 .001

Singlecaretaker^b 12.5 0.320 0.11,0.52 .003 0.23 −0.05,0.50 .108

Nosiblings 8.9 0.080 −0.16,0.32 .523

Maternaleducation≤12y^b 44.2 0.210 0.07, 0.34 .003 −0.05 −0.22,0.12 .567

Paternaleducation≤12y^b 60.6 0.320 0.18, 0.46 <.001 0.07 −0.10,0.24 .422

≥1parentoriginatingoutsideEuropeor

NorthAmerica 2.5 0.060 −0.38,0.49 .803

Ruralliving(<20000inhabitants)^b 65.8 0.320 0.18, 0.47 <.001 0.36 0.20,0.52 <.001 Generalhealthofthechild

Prematurity(gestationalweek<37) 6.4 0.160 −0.12,0.43 .272

Caries^b 18.7 0.210 0.04, 0.39 .020 0.12 −0.09,0.34 .255

Treatmentwithantibiotics^b 58.7 0.120 −0.01,0.26 .077 0.11 −0.04,0.27 .144

Chronicdiseases^f 1.6 0.140 −0.40,0.69 .603

Asthmamedicationafter2yofage 11.6 0.080 −0.14,0.29 .477

Note: DependentVariable:Bodymassindex(BMI)z-scoreinthirdgrade.

Abbreviation:CI,ConfidenceInterval.

aAdjustedR² = 17.8%.

bVariablesincludedinmultivariableanalysis.

cUnstandardizedregressioncoefficient.

dNoteatingallofthefourdailyprincipalmeals>5times/week.

eN=551.

fCoeliacdisease,diabetes,cerebralparesis,autism,chromosomedisordersandcongenitalmalformations.

children,adolescentsandadults.⁸However,ithasbeenarguedthat thedifferencesbetweenthecontrolandinterventiongroupsofthe PROBITstudyweretoosmalltoresultinadifferenceonchildobe- sity,andthattheresultmaynotbeeasilygeneralised,astheprev- alenceofoverweightandobesitywassubstantiallylowerthanfor instanceintheUS.²⁰Furthermore,inhigh-incomecountries,suchas Norway,breastfeedingandthedurationofbreastfeedingareassoci- atedwithanumberofbeneficialhealthandlifestylefactors.^15,21The riskofincreasingBMIwithunfavourablesocialcharacteristicsinthe currentstudy(Table2)underscorestheimportanceofadjustingfor suchfactorswhenassessingtheimportanceofbreastfeedingperse.

Studiesfromlow-andmedium-incomecountriesmaynotprovide avalidcomparisonsincebreastfeedingisnotnecessarilyassociated with the same social and lifestyle determinants as in high-income countries.^22,23Giventherelativehomogeneityofourpopulationand the lack of appreciable differences in weight and height between theparticipantsandnon-participants,wesuggestthatthemainpo- tentialconfounderswereaccountedfor,andthatpotentialresidual confounding was limited.²⁴ We, therefore, suggest that the lack of asignificantassociationbetweenbreastfeedingandoverweightand obesityatearlyschoolageisavalidfindinginapopulationfroma high-incomecountry.ApreviousstudyfromNorwayandBelgiumhas alsosuggestedthatenvironmentalandgeneticbackgroundsareof greaterimportanceforgrowththanbreastfeeding,eveninsub-popu- lationsofbreastfedinfantswithnon-smokingmothers.⁵

Fromthiscohort,wehavepreviouslyreportedthatexclusivebreast- feedingforatleast4monthswasnotsignificantlyassociatedwitharisk ofoverweightandobesityatpre-schoolage.²⁵Thepresentstudyadds thattherewerenosignificanteffectsonBMIorriskofoverweightor obesityinthethirdgrade,anageatwhichchildrenarebecomingmore independent. This study also adds that there were no indications of dose-responsiverelationshipsbetweentheextentordurationofbreast- feedingandBMIz-scoreoroverweightorobesityinthethirdgrade.

Akeystrengthofthisstudywasthecomprehensivedataobtained onbreastfeedingduration,sociodemographicfactorsandhealthand lifestylecharacteristicsofthechildrenandtheirfamilies.Therelatively lowparticipationratewasaweakness,buttheparticipatingchildren

andtheirfamilieswereconsideredrepresentativeoftheregionalpop- ulationsincetheiranthropometricmeasurementsandsexdistribution weresimilartothosewhodidnotparticipate.Also,wedidnothave data on maternal BMI during pregnancy. Such data could probably havecontributedinexploringtherelationshipbetweendeterminants ofearlylifeandBMIinchildhood.²⁶Informationwasvolunteeredby theparentswhenthechildrenwere5yearsoldandmaybeinaccurate forinstanceduetorecallbias.However,studieshaveshownthata recallofdurationofbreastfeedingisquiteaccurateafterthree²⁷six²⁸ and even 20years,²⁹ although therewere slight overestimations of durationofbreastfeeding.Thismayalsobetrueforthecurrentco- hortsincethemeandurationofexclusivebreastfeedingwasslightly longerthanreportedinpreviousstudiesfromotherpartsofNorway wheredatawerecollectedprospectively.^13,15Lessaccuraterecallon breastfeeding duration has been reported among maternal smokers and multiparous mothers,²⁸ but we found no significant interaction for duration of breastfeeding and maternal smoking.We, therefore, assumethatmaternalsmokinglikelyhadlittleimpactontheresults ofourstudy.Unfortunately,ourdatadidnotincludeinformationon parity.AnotherlimitationisthepossibilityofatypeIIerrorofanot foundeffect,asourpopulationhadalowfrequencyofnotbreastfed children.ThismayleadtoalowerpowerforourstudyAnotherfactor iswhetherparentaleducationisthebestindicatorofsocio-economic status,orwhetheradditionalinformationonfamilyincomeandoccu- pationwouldhavegivenamoreaccuratepicture.

5  | CONCLUSION

This study on 8-year-old Norwegian children did not corroborate previousobservationalstudieswhichsuggestthatbreastfeedingre- ducestheriskofchildhoodoverweightandobesity.

ACKNOWLEDGEMENTS

TheauthorswouldliketothankBiostaticianMathieuRoelants,PhD, UniversityofLeuvenforadviceonthestaticalanalyses.

TA B L E 3  Adjustedregressionanalysesforallbreastfeedingexposures Linear regression (dependent variable: BMI

z‐score) Logistic regression (dependent variable: OWOB)

Coef^a 95% CI P‐value % Odds Ratio 95% CI P‐value

Everbreastfed^b −0.06 −0.34,0.21 0.64 20.1 0.99 0.48, 2.02 0.97

<4moofexclusivebreastfeeding^c 0.06 −0.11,0.21 0.51 0.06 1.06 0.67, 1.66 0.80

Exclusivebreastfeeding(months)^d 0.00 −0.03,0.04 0.80 20.3 0.98 0.90, 1.08 0.77

Partialbreastfeeding(months)^e 0.00 −0.01,0.01 0.94 19.0 1.02 0.99, 1.06 0.25

Abbreviation:CI,ConfidenceInterval.

aUnstandardizedregressioncoefficient.

bAdjustedforallvariablesincludedinTable2except<4moofexclusivebreastfeeding,exclusivebreastfeedingandpartialbreastfeeding.

cAdjustedforallvariablesincludedinTable2excepteverbreastfed,exclusiveandpartialbreastfeeding.

dAdjustedforallvariablesincludedinTable2excepteverbreastfed,<4moofexclusivebreastfeeding,andpartialbreastfeeding.

eAdjustedforallvariablesincludedinTable2excepteverbreastfed,<4moofexclusivebreastfeedingandexclusivebreastfeeding.

CONFLIC T OF INTEREST

Theauthorshavenoconflictingintereststodeclareandhavesigned the ICMJE uniform disclosure form at http://www.blackwellpublis hing.com/pdf/apa_contributors.pdf

ORCID

Asborg A. Bjertnæs https://orcid.org/0000-0002-0504-4606 Petur B. Juliusson https://orcid.org/0000-0002-7064-1407 Trond Markestad https://orcid.org/0000-0002-4725-1769

REFERENCES

1. Afshin A, Forouzanfar MH, Reitsma MB, et al. Health effects of overweight and obesity in 195 countries over 25 years.N Engl J Med.2017;377:13-27.

2. HrubyA,MansonJE,QiL,etal.Determinantsandconsequencesof obesity.Am J Public Health2016;106(9):1656-1662.

3. WHO. Exclusive breastfeeding for optimal growth, development and health of infants [internet]. https://www.who.int/elena/title s/exclusive_breastfeeding/en/WorldHealthOrganizationAccessed October13,2018.

4. WHOMulticentreGrowthReferenceStudyGroup.Breastfeeding in the WHO Multicentre Growth Reference Study.Acta Paediatr.

2006;450:16-26.

5. Juliusson PB, Roelants M, Hoppenbrouwers K, Hauspie R, Bjerknes R. Growth of Belgian and Norwegian children com- pared to the WHO growth standards: prevalence below -2 and above+2SDandtheeffectofbreastfeeding.Arch Dis Childhood.

2011;96(10):916-921.

6. HornellA,LagstromH,LandeB,ThorsdottirI.Breastfeeding,intro- ductionofotherfoodsandeffectsonhealth:asystematicliterature reviewforthe5thNordicNutritionRecommendations.Food Nutr Res.2013;57:20823.

7. WHO.10factsonbreastfeeding[internet].https://www.who.int/

features/factfiles/breastfeeding/en/:WorldHealthOrganization;

AccessedJanuary08,2018.

8. HortaBL,LoretdeMolaC,VictoraCG.Long-termconsequences of breastfeeding on cholesterol, obesity, systolic blood pressure andtype2diabetes:asystematicreviewandmeta-analysis.Acta Paediatr.2015;104:30–37.

9. Arenz S, Ruckerl R, Koletzko B, von Kries R. Breast-feeding and childhood obesity–a systematic review.Int J Obesity Relat Metab Disord.2004;28:1247-1256.

10. Giugliani ERJ, Horta BL, Loret de Mola C, Lisboa BO,Victora CG. Effect of breastfeeding promotion interventions on child growth: a systematic review and meta-analysis.Acta Paediatr.

2015;104:20-29.

11. MartinRM,KramerMS,PatelR,etal.Effectsofpromotinglong- term,exclusivebreastfeedingonadolescentadiposity,bloodpres- sure,andgrowthtrajectories:asecondaryanalysisofarandomized clinicaltrial.JAMA Pediatr. 2017;171:e170698.

12. Smithers LG, Kramer MS, Lynch JW. Effects of breastfeeding on obesity and intelligence: causal insights from different study de- signs.JAMA Pediatr.2015;169:707-708.

13. KristiansenAL,LandeB,OverbyNC,AndersenLF.Factorsassoci- atedwithexclusivebreast-feedingandbreast-feedinginNorway.

Public Health Nutr.2010;13:2087-2096.

14. Helsedirektoratet. Nasjonal faglig retningslinje for spedbarn- sernæring. [internet]; 2017. https://www.helsedirektoratet.no/

retningslinjer/spedbarnsernaering.

15. HalvorsenMK,LangelandE,AlmenningG,etal.Breastfeedingsur- veyedusingroutinedata.Tidsskr Nor laegeforen.2015;135:236–241.

16. StatisticsNorway.StatisticalyearbookofNorway2010[internet].

https://www.ssb.no/en/befolkning/artikler-og-publikasjoner/stati stical-yearbook-of-norway-2010.

17. JuliussonPB,RoelantsM,NordalE,etal.Growthreferencesfor0–19 year-oldNorwegianchildrenforlength/height,weight,bodymass indexandheadcircumference.Ann Human Biol.2013;40:220-227.

18. Cole TJ, Lobstein T. Extended international (IOTF) body mass indexcut-offsforthinness,overweightandobesity.Pediatr Obes.

2012;7:284-294.

19. NorwegianScientificCommitteeforFoodSafetyVKM.Benefitand riskassessmentofbreastmilkforinfanthealthinNorway[internet].

https://vkm.no/english/riskassessments/allpublications/benef itandriskassessmentofbreastmilkforinfanthealthinnorway.4.27ef9 ca915e07938c3b2a6df.html2013.

20. DieterichCM,FeliceJP,O’SullivanE,RasmussenKM.Breastfeeding andhealthoutcomesforthemother-infantdyad.Pediatr Clin North Am. 2013;60:31.

21. Victora CG, Bahl R, Barros AJD, et al. Breastfeeding in the 21st century: epidemiology, mechanisms, and lifelong effect.Lancet 2016;387:475-490.

22. BrionMJ,LawlorDA,MatijasevichA,etal.Whatarethecausalef- fectsofbreastfeedingonIQ,obesityandbloodpressure?Evidence from comparing high-income with middle-income cohorts.Int J Epidemiol.2011;40:670-680.

23. FallCH,BorjaJB,OsmondC,etal.Infant-feedingpatternsandcar- diovascularriskfactorsinyoungadulthood:datafromfivecohorts inlow-andmiddle-incomecountries.Int J Epidemiol.2011;40:47-62.

24. Kramer MS, Oken E, Martin RM. Infant feeding and adiposity:

scientific challenges in life-course epidemiology.Am J Clin Nutr.

2014;99:1281-1283.

25. DonkorHM,GrundtJH,JuliussonPB,etal.Socialandsomaticde- terminantsofunderweight,overweightandobesityat5yearsof age:aNorwegianregionalcohortstudy.BMJ Open2017;7:e014548.

26. YuZ,HanS,ZhuJ,SunX,JiC,GuoX.Pre-pregnancybodymassindex inrelationtoinfantbirthweightandoffspringoverweight/obesity:a systematicreviewandmeta-analysis.PLoS ONE 2013;8:e61627.

27. LiR,ScanlonKS,SerdulaMK.Thevalidityandreliabilityofmaternal recallofbreastfeedingpractice.Nutr Rev.2005;63:103-110.

28. AmissahEA,KancherlaV,KoYA,LiR.Validationstudyofmaternal recallonbreastfeedingduration6yearsafterchildbirth.J Human Lact.2017;33:390-400.

29. Natland ST, Andersen LF, Nilsen TI, Forsmo S, Jacobsen GW.

Maternalrecallofbreastfeedingdurationtwentyyearsafterdeliv- ery. BMC Med Res Methodol. 2012;12:179.

How to cite this article:BjertnæsAA,GrundtJH,DonkorHM, etal.Nosignificantassociationsbetweenbreastfeeding practicesandoverweightin8-year-oldchildren.Acta Paediatr.

2019;00:1–6. https://doi.org/10.1111/apa.14937