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Article 5: Mobile phone use, behavioural problems and concentration capacity in adolescents: a prospective study

Katharina Roser ^1,2, Anna Schoeni ^1,2 and Martin Röösli ^1,2

1 Swiss Tropical and Public Health Institute, Basel, Switzerland

2 University of Basel, Basel, Switzerland

Published in the journal International Journal of Hygiene and Environmental Health, 2016.

219(8):759-769. doi: 10.1016/j.ijheh.2016.08.007

ContentslistsavailableatScienceDirect

International Journal of Hygiene and Environmental Health

j ourna l h o m e p a g e :w w w . e l s e v i e r . c o m / l o c a t e / i j h e h

Mobile phone use, behavioural problems and concentration capacity in adolescents: A prospective study

KatharinaRoser^a,b,AnnaSchoeni^a,b,MartinRöösli^a,b,∗

aSwissTropicalandPublicHealthInstitute,Socinstrasse57,P.O.Box,CH-4002Basel,Switzerland

bUniversityofBasel,Petersplatz1,CH-4003Basel,Switzerland

a rt i c l e i n f o

Articlehistory:

Received2June2016

Receivedinrevisedform4August2016 Accepted20August2016

Theaimofthisstudyistoprospectivelyinvestigatewhetherexposuretoradiofrequency electromag-neticfields(RF-EMF)emittedbymobilephonesandotherwirelesscommunicationdevicesisrelatedto behaviouralproblemsorconcentrationcapacityinadolescents.

TheHERMES(HealthEffectsRelatedtoMobilephonEuseinadolescentS)studysampleconsistedof 439Swissadolescentsaged12–17years.BehaviouralproblemswereassessedusingtheStrengthsand DifficultiesQuestionnaire(SDQ),concentrationcapacityoftheadolescentswasmeasuredbymeansofa standardizedcomputerizedcognitivetestnamedFAKT.Cross-sectionalandlongitudinal(1yearof follow-up)analyseswereperformedtoinvestigatepossibleassociationsbetweenbehaviouralproblemsand concentrationcapacityanddifferentexposuremeasures:self-reportedandoperator-recordedwireless communicationdeviceuse,cumulativeRF-EMFbrainandwholebodydoseandmeasuredpersonal RF-EMFexposure.

Inthecross-sectionalanalysesbehaviouralproblemswereassociatedwithseveralself-reported wire-lessdeviceusemeasuresbutnotoperator-recordedmobilephoneusemeasures,concentrationcapacity wasassociatedwithseveralself-reportedandoperator-recordedexposures.Thelongitudinalanalyses pointtowardsabsenceofassociations.

The lack of consistent exposure-response patterns in the longitudinal analyses suggests that behaviouralproblemsandconcentrationcapacityarenotaffectedbytheuseofwireless communica-tiondevicesorRF-EMFexposure.Informationbiasandreversecausalityarelikelyexplanationsforthe observedcross-sectionalfindings.

©2016ElsevierGmbH.Allrightsreserved.

1. Introduction

Mobilephonesarenowadaysomnipresent,inparticularamong adolescents.Arecentrepresentativesurveyin1086Swiss adoles-centsaged12–19yearsrevealedthat98%oftheadolescentsowna mobilephoneand97%ofthesedevicesaresmartphones(Willemse etal.,2014).Furthermore,theuseofthesedevicesisfrequent,94%

oftheadolescentsusedtheirmobilephonedailyorseveraltimes perweekforexchangingmessagesviainternet-basedapplications, 87%forbrowsingtheinternetand53%forgaming(Willemseetal., 2014).Thiswidespreadandintensiveusehascreatedconcernthat itmaycausebehaviouralorconcentrationproblems,whichbelong tothemostcommonhealthcomplaintsofadolescents.

∗ Correspondingauthorat:SwissTropicalandPublicHealthInstitute,Socinstrasse 57,P.O.Box,CH-4002Basel,Switzerland.

E-mailaddresses:[email protected](K.Roser),

[email protected](A.Schoeni),[email protected](M.Röösli).

Swisspaediatriciansestimatedthepercentageofchildrenwith attentiondeficithyperactivitydisorder(ADHD)orconduct prob-lemsseenintheirpracticeat9%(In-Albonetal.,2010).InaGerman studyincluding7000adolescentsaged11–17yearsparent-rated behaviouralproblemsmeasuredbytheStrengthsandDifficulties Questionnaire(SDQ,(Goodman,1997))werefoundin7%ofthe adolescents(Höllingetal.,2007).Amongspecificproblems, con-ductproblemsweremostfrequentlyreported(14%),followedby problemswithpeers(13%)andemotionalsymptoms(10%). Hyper-activitywasreportedfor 7%of theadolescentsand 4%showed antisocialbehaviour(Höllingetal.,2007).Among825Swiss7th gradestudentsantisocialbehaviourwasonaverageexhibitedonce amonth(Mülleretal.,2015).

InSweden,concentrationdifficultieswereamongthemost fre-quentreportedhealthcomplaintsinadolescents(Söderqvistetal., 2008)and in Germany,32% of theadolescents participatingin a measurement studyreportedtohave concentrationproblems

http://dx.doi.org/10.1016/j.ijheh.2016.08.007

760 K.Roseretal./InternationalJournalofHygieneandEnvironmentalHealth219(2016)759–769

(Heinrichetal.,2010).InChineseadolescents,theprevalenceof inattentionwasreportedtobeashighas70%(Zhengetal.,2014).

A possible link between behavioural problems and RF-EMF exposurehasbeeninvestigatedin1508adolescentsfromGermany using24hpersonalRF-EMFmeasurementsforexposure assess-ment (Thomas et al., 2010b). In the highest exposure group (4thquartile)theriskforoverallbehaviouralproblems(adjusted OR=2.2;95%CI:1.1–4.5)andconductproblems(adjustedOR=3.7;

95%CI:1.6–8.4)wasfoundtobeelevated.ASwedishstudyfound the duration of mobile phone and cordless phone calls associ-atedwithself-reported concentrationdifficultiesinadolescents (Söderqvistet al.,2008)and thenumber ofmobilephone calls wasassociatedwithimpairedattentionperformanceinAustralian adolescents(Abramsonetal.,2009).Incontrast,measuredRF-EMF exposureanddurationofmobilephoneusewerenotassociated withacuteconcentrationproblemsin1508Germanadolescents (Heinrichetal.,2010)andmobilephonecallswerenotfoundtobe associatedwithADHDsymptomsin2422Koreanchildren(Byun etal.,2013)orinattentionin7102Chineseadolescents(Zhengetal., 2014).Butinterestingly,theyfoundmobilephoneuseforplaying games(Byunetal.,2013)andthetimespentonthemobilephone forentertainment(Zhengetal.,2014)beingassociatedwithADHD symptomsandinattention,respectively.However,allthese stud-ieswereofcross-sectionaldesignandprospectivestudiesarestill missing.

Afurtherlimitationistheuseofself-reportedmobileorcordless phoneuseasproxyforRF-EMFexposure,becausesuchreportsare inaccurate(Aydinetal.,2011;Inyangetal.,2009)anddonottake intoaccountothersourcesthatcontributetotheRF-EMF expo-sureof adolescentssuch as theuse of computers, laptops and tabletsconnectedtowirelessinternet(WLAN)ortheexposurefrom fixedsitetransmittersforbroadcastandmobile telecommunica-tion(Laueretal.,2013;Roseretal.,2015a).

To overcome theselimitations and in linewith the recom-mendationsoftheWorldHealthOrganisation(WHO)toconduct prospectivecohortstudiesinchildrenandadolescentswith out-comesincludingbehaviouraldisorderswithahighpriority(WHO, 2010),theHERMES(HealthEffectsRelatedtoMobilephonEuse inadolescentS)studywassetup.TheHERMESstudyisa prospec-tivecohortstudywithaoneyearfollow-upperiod.Todifferentiate betweeneffects fromRF-EMFexposureandeffects frommobile phoneuseperse,anRF-EMFdosemeasurewasdevelopedtaking intoaccountvariousRF-EMFsourcesandincludingprospectively collectedoperatordata(Roseretal.,2015a).ApplyingthisRF-EMF dosemeasureincombinationwithusemeasureswillhelpto dis-entanglepossibleeffectsfromRF-EMForfromtheuseperse.

TheaimofthisstudyconductedintheframeworkoftheHERMES studywastoprospectivelyinvestigatewhetherRF-EMFexposure frommobilephonesandotherwirelesscommunicationdevicesis relatedtobehaviouralproblemsorconcentrationcapacityin ado-lescents.

2. Methods

2.1. HERMESstudy

ThebaselineinvestigationoftheHERMESstudywasconducted betweenJune2012andMarch2013inCentralSwitzerland.The follow-up investigationwas conductedapproximately oneyear later. The study participantsfilled in a paperand pencil ques-tionnaire and performeda cognitive concentrationtest using a standardized,computerizedcognitivetestbattery.The investiga-tiontookplaceinschoolduringschooltimeandwassupervisedby

fortheparentsweredistributedandreturneddirectlytothestudy managers.

Ethicalapprovalfortheconductofthestudywasreceivedfrom theethicalcommitteeofLucerne,SwitzerlandonMay9,2012.

2.2. Exposures

2.2.1. Self-reportedexposure

Theadolescents’questionnaireincludedquestionsonmobile phoneuse:calldurationwithownandanyothermobilephone, durationofdatatrafficonthemobilephoneandnumberofallkind oftextmessagessent(shortmessagesystem(SMS)aswellas mes-sagessentbyinternet-basedapplications).Furthermore,thecall durationwithcordless(fixedline)phonesandthedurationof gam-ingoncomputer,laptops,tabletsandTVwerereported.Thestudy participantswereaskedtorefertoanaverageuseperdayandthe periodofsixmonthspriortotheinvestigation.Thenumberoftext messagessentandthedurationofgamingoncomputerandTVare notoronlymarginallyrelevantforRF-EMFexposureandwerethus usedasnegativeexposurecontrolvariablesintheanalyses.

2.2.2. Objectiveexposure

Asubsampleofthestudyparticipantsandtheirparentsgave informed consent obtainingobjectively recorded mobilephone usedatafromthemobilephoneoperators.Thesedataincluded durationofeachcallandthenetwork(GlobalSystemforMobile Communications(GSM)orUniversalMobileTelecommunications System (UMTS)) at which it started, number of SMS sent and amountof datatrafficvolume transmitted.Data wereobtained forupto18months,sixmonthsbeforebaselineuntilfollow-up investigationoneyearlater.

2.2.3. RF-EMFdosemeasures

TocalculatethecumulativeRF-EMFdoseofthebrainandthe wholebodyfortheparticipatingadolescents,anintegrativeRF-EMF exposuresurrogateincludingvariousfactorscontributingto near-fieldandfar-fieldRF-EMFexposurewasdeveloped(Roseretal., 2015a).The near-fieldcomponent combinesthe exposurefrom theuseofwirelesscommunicationdevices(mobilephones, cord-lessphones,computers,laptopsandtabletsconnectedtoWLAN).

Thefar-fieldcomponent aggregatestheexposurefrom environ-mentalsources.Topredicttheexposuresfromradioandtelevision broadcasttransmittersandmobilephonebasestationsageospatial propagationmodelwasused(Bürgietal.,2010,2008).Exposures fromcordlessphoneandWLANbasestationsaswellasother peo-ple’smobilephoneswereestimatedbymeansoflinearregression modelscalibratedonthepersonalmeasurementdatafor95study participants(Roseretal.,2015a).Foreachoftheconsidered expo-surecircumstances,averagespecificabsorptionrates(SAR)forthe brainandthewholebodywerederivedfromtheliterature(Gati etal.,2009;Hadjemetal.,2010;Huangetal.,2014;Laueretal., 2013;Perssonetal.,2012;SEAWIND,2013;Vrijheidetal.,2009).

Toobtainacumulativedailybrainandwholebodydoseforeach studyparticipant,theSARvaluesweremultipliedbytheaverage exposuredurationperdayforeachexposuresituationandsummed uptoonesinglebrainandwholebodydosemeasure.This calcula-tionwasdonetwice:first,forthewholesampleusingself-reported duration of mobile phone calls;and secondly, for the subsam-plewithoperator-recordeddatamobilephonecalldurationwas derivedfromthemobilephoneoperatorrecords.AllotherRF-EMF dosefactorswereidenticalforbothcalculations.

2.2.4. PersonalRF-EMFmeasurements

Asanadditionalexposureproxyweconsideredpersonal

RF-HERMESstudyparticipants.Theadolescentscarriedaportable RF-EMFmeasurementdeviceforthreeconsecutivedaysandfilledin atime-activitydiary.Thesemeasurementsaredescribedindetail in (Roser etal. underpreparation).Personal measurementdata wereavailablefor91oftheHERMESparticipants.Exposuresforthe personalmeasurementsanalysisincludedaveragepersonal down-linkexposure(exposurefrommobilephonebasestations),fixed sitetransmittersexposure(exposurefrommobilephonebase sta-tionsandtelevisionbroadcasttransmitters),totalRF-EMFexposure andtotalRF-EMFexposurewithoutuplink(exposurefrommobile phonehandsets)overthewholemeasurementperiodofthe per-sonalmeasurements.

2.3. Outcomes

2.3.1. Behaviouralproblems

The self-reported SDQ in the questionnaire of the adoles-cents(referredtoasSDQAdolescents) andtheparent-ratedSDQ intheparents’questionnaire(referredtoasSDQParents)assess behavioural and affective problems of adolescents (Goodman, 1997).Theyconsistoffivescalesassessingemotionalsymptoms, conduct problems, hyperactivity/inattention, peer relationship problems andprosocialbehaviour onfive itemseach answered ona 3-pointLikert scale. Atotal difficulties score can be calcu-latedbysummingupthescoresforemotionalsymptoms,conduct problems, hyperactivity/inattention and peerrelationship prob-lemsandthetotalstrengthsscorereferstotheprosocialbehaviour scale.Higherscoresonthescalesassessingdifficulties(emotional symptoms,conductproblems,hyperactivity/inattention,andpeer relationshipproblems)meanmoredifficulties;ahigherscoreon the prosocial behaviour scale means more strengths. Individu-alswithatotaldifficultyscoreof≥20(SDQAdolescents)and≥17 (SDQ Parents) are considered tohave difficulties.For the diffi-cultysubscalesthecorrespondingcut-offsare7and5(emotional symptoms), 5 and 4 (conduct problems), 7 and 7 (hyperactiv-ity/inattention)and6and4(peerrelationshipproblems)forthe SDQAdolescentsandSDQParents,respectively.Individuals scor-ing≤4 on the total strengths scale (SDQ Adolescents and SDQ Parents)areconsideredtohavea problematiclackofstrengths.

ReliabilityandvalidityoftheSDQwereshowntobesatisfactoryina nationwideBritishsampleofadolescents(Cronbach’salphaof0.73 measuringinternalconsistency,reteststabilityof0.62)(Goodman, 2001).Furthermore,theGermanSDQwasshowntobejustasuseful andvalidastheEnglishoriginalscaleintermsofsimilar facto-rialstructure,reliabilityandvalidationofthescales(Klasenetal., 2003).Mainanalysesincludebehaviouralproblemsmeasuredby theSDQAdolescents;resultsoftheanalysesusingtheSDQParents arepresentedintheSupplementarymaterial.

2.3.2. Concentrationcapacity

Weuseda standardized,computerizedcognitivetestbattery named FAKT-II (Frankfurter Adaptiver Konzentrationsleistungs-Test-II, (Moosbrugger and Goldhammer, 2007))to measure the concentrationcapacityoftheadolescents.Concentrationcapacity measuresincludedhomogeneity,powerandaccuracyof concen-tration.Bymeansofdiscriminationtasks,theparticipanthadto discriminateasaccuratelyandasquicklyaspossiblebetween tar-getandnon-targetitemsbypressing“0”fornon-targetitemsand

“1”fortargetitems.Itemswitheithertwoorthreepointsineither acircleorasquareappeared.Targetitemswereeithertwopoints inasquareorthreepointsinacircle.Othercombinationsacted asnon-targetitems.Beforestartingthe6-mintest,theparticipant performedatrial-run.TheFAKTisanadaptivetestadjustingthe speedoftheitemdisplayaccordingtothespeedoftheanswers

Homogeneityofconcentrationisameasureoftheuniformityof theworkingspeed.Itmeasuresthevarianceofthetimeanitemis displayed.Thehigherthehomogeneityofconcentration,themore uniformthestudyparticipantworked.Powerofconcentrationisa measureoftheworkingspeed.Itmeasuresthenumberofdisplayed itemsper100s.Thehigherthepowerofconcentration,thefaster thestudyparticipantworkedandthemoreitemsweredisplayed.

Accuracyofconcentrationisameasureoftherelativecorrectness.

Itmeasuresthepercentageofnon-falseitemsthathavebeen pro-cessed.Thehighertheaccuracyofconcentration,themoreprecise thestudyparticipantworked.Thetestwasconductedonceat base-lineandonceatfollow-upinvestigation.

2.4. Statisticalanalysis

Threemain analyseswereperformedto investigatepossible associations between behavioural problems and concentration capacityanddifferentexposuremeasures.

Theexposuremeasuresincluded:

1)Negativeexposurecontrolvariables(usagenotoronlymarginally relatedtoRF-EMFexposure):Self-reported:durationofgaming onthecomputerorTV(min/day),frequencyoftextmessages sent(x/day).

Operator-recorded:frequencyofSMSsent(x/day).

2)Radiationrelatedfactors inthecontextof mobilephoneuse (usagerelatedtoRF-EMFexposure):Self-reported:durationof datatrafficonthemobilephone(min/day),durationofcordless phonecalls(min/day),durationofmobilephonecalls(min/day).

Operator-recorded:volumeofdatatrafficonthemobilephone (MB/day),durationofmobilephonecalls(min/day).

3)RF-EMF exposure (cumulative RF-EMF dose): Whole sample:

braindose(mJ/kg/day),wholebodydose(mJ/kg/day)basedon self-reportedexposuredata.

Operatorsample:braindose(mJ/kg/day),wholebodydose (mJ/kg/day) based on operator-recorded mobile phone call durationandself-reporteddataforotherwirelessdeviceuse.

4)PersonalRF-EMFmeasurements:Downlinkexposure(exposure frommobilephonebasestations),fixedsitetransmitters expo-sure(exposurefrommobilephonebasestationsandtelevision broadcasttransmitters),total RF-EMFexposure,total RF-EMF exposurewithoutuplink(exposurefrommobilephone hand-sets).

Thethreemainanalyseswerethefollowing:

a)A cross-sectional mixed model analysis using baseline and follow-upexposureandoutcomevariables.

b)Alongitudinalanalysistoinvestigatewhethercumulative expo-surewasfollowedbyachangeinoutcome.

c)A cross-sectional analysis of the follow-up outcomes with respecttopersonal RF-EMF measurementsin thesubsample withpersonalmeasurements.

Thecross-sectionalmixedmodelanalysis(a)wasbasedona combineddatasetofbaselineandfollow-updataforboth, expo-sureandoutcomevariables.Exposurereferredtotheaverageuse ordosewithinsixmonthspriortotheinvestigation.Forthe lon-gitudinal analysis (b)changes in outcomes(difference between follow-upandbaseline)wererelatedtothecumulativeexposure betweenbaselineandfollow-upinvestigation.Forbetter interpre-tationcumulativeexposurebetweenbaselineandfollow-upwas expressedasaveragedailyvalues.Thecross-sectionalanalysisin thepersonalmeasurementssubsample(c)wasbasedonthe aver-agemeasuredRF-EMFexposureduringthreeconsecutivedaysand

762 K.Roseretal./InternationalJournalofHygieneandEnvironmentalHealth219(2016)759–769

between7.3monthsbeforeand1monthafterthefollow-up inves-tigation.

Allmodelswereadjustedforage,sex,nationality,schoollevel (college preparatory high school or highschool), frequency of physicalactivity,frequencyofalcohol consumption andhighest educationalleveloftheparents.Inthelongitudinalanalysis,models wereadditionallyadjustedforchangeinheightbetweenbaseline andfollow-upandtimebetweenbaselineandfollow-up.

Tobeabletocomparetheeffectsizesofthedifferentexposure measures,coefficients werestandardizedusingtheinterquartile rangeofthecorrespondingexposurevariable.

For sensitivity analysis, the exposure measures were cate-gorisedintoareferencecategory(<50thpercentile)andtwoother categoriesdefinedby50th–75thpercentileand>75thpercentile.

Linearregressionimputation(14missingvaluesatbaselineand 10missingvaluesatfollow-upforfrequencyofalcohol consump-tion;7missingvaluesatbaselineand6missingvaluesatfollow-up forinformationonheight)orimputationofacommoncategory(2 missingvaluesatbaselineand1missingvalueatfollow-upfor fre-quencyofphysicalactivity;60missingvaluesforeducationallevel oftheparents)wasusedtoimputemissingvaluesinthecovariate variables.StatisticalanalyseswerecarriedoutusingSTATAversion 12.1(StataCorp,CollegeStation,USA).Figuresweremadewiththe softwareRusingversionRforWindows3.0.1.

All procedures performed in studies involving human par-ticipantswere in accordance withthe ethicalstandards of the institutionaland/ornationalresearchcommitteeandwiththe1964 Helsinkideclarationanditslateramendmentsorcomparable eth-icalstandards.

Informedconsentwasobtainedfromallindividualparticipants includedinthestudy.

3. Results

3.1. Studyparticipants

439students(participationrate:36.8%)withameanageof14 years(rangingfrom12to17years)from24schools(participation rate:19.1%)inruralandurbanareasinCentralSwitzerland partici-patedinthebaselineinvestigationoftheHERMESstudy.425study participants(participationrate:96.8%)tookpartinthefollow-up investigation,whichwasonaverage12.8monthslater.412(93.8%) and416(97.9%)studyparticipantsownedamobilephoneat base-lineandatfollow-up,respectively.60.4%oftheparticipantswere female,79.3%wereSwiss,14.1%hadmixednationalityand6.6%

hadaforeignnationality.22.6%attendedacollegepreparatoryhigh school.71.8%oftheparticipantsreportedtobephysicallyactiveup tothreetimesaweek.Twothirdoftheparticipants(68.8%)didnot consumealcoholatall,anotherthird(30.5%)uptoonceaweek.

Forhalfoftheparents(50.3%),atrainingschoolwasthehighest educationallevelachieved,30.1%attendedacollegeofhigher edu-cation,8.2%auniversity,7.5%acollegeofpreparatoryhighschool, 3.2%themandatoryschooland0.7%hadnoeducation.Theoperator samplewasslightlyolderandmoreparticipantsattendeda col-legepreparatoryhighschool(28.3%).Thesubsamplewithpersonal RF-EMFmeasurementscontainedmoreSwissandfewer adoles-centswithmixednationalitycomparedtothewholesample.The othercovariatesweresimilarlydistributedforthewholesample, theoperatorsampleandthepersonalmeasurementsample.

Forhalfoftheparents(50.3%),atrainingschoolwasthehighest educationallevelachieved,30.1%attendedacollegeofhigher edu-cation,8.2%auniversity,7.5%acollegeofpreparatoryhighschool, 3.2%themandatoryschooland0.7%hadnoeducation.Theoperator samplewasslightlyolderandmoreparticipantsattendeda col-legepreparatoryhighschool(28.3%).Thesubsamplewithpersonal RF-EMFmeasurementscontainedmoreSwissandfewer adoles-centswithmixednationalitycomparedtothewholesample.The othercovariatesweresimilarlydistributedforthewholesample, theoperatorsampleandthepersonalmeasurementsample.