Exposure to secondhand tobacco smoke and child behaviour – results from a cross-sectional study among preschool children in Bavaria

REGULAR ARTICLE

Exposure to secondhand tobacco smoke and child behaviour – resultsfrom a cross-sectional study among preschool children in BavariaD Twardella ([email protected])1, G Bolte1, H Fromme1, M Wildner2, R von Kries3, the GME Study Group1.Bavarian Health & Food Safety Authority, Department of Environmental Health, Oberschleissheim, Germany2.Bavarian Health & Food Safety Authority, Department of Health Promotion and Social Medicine, Oberschleissheim, Germany3.Institute for Social Paediatrics & Adolescent Medicine, Ludwig Maximilians University, Munich, Germany

KeywordsChild behaviour, Exposure to secondhand tobaccosmoke, Maternal smoking

CorrespondenceD Twardella, Bavarian Health and Food SafetyAuthority, Department of Environmental Health,Veterinaerstr. 2, 85764 Oberschleissheim,Germany.Tel: +49-89-315-60-166 |Fax: +49-89-315-60-835 |Email: [email protected]

Received13 May 2009; revised 30 July 2009;accepted 7 September 2009.

DOI:10.1111/j.1651-2227.2009.01522.x

AbstractAim: To evaluate the association of postnatal exposure to secondhand tobacco smoke on child-

hood behavioural problems after taking maternal smoking during pregnancy into account.

Methods: In a cross-sectional survey of preschool children in Bavaria, exposure to secondhand

tobacco smoke in the child’s home was assessed via a parent questionnaire. The Strength and Difficul-

ties Questionnaire (SDQ) was applied to assess child’s behaviour. The association with secondhand

tobacco smoke exposure was assessed for ‘probable’ outcomes of the problem subscales and of pro-

social behaviour.

Results: Among 5494 children (48% female), the SDQ indicated behavioural problems in up to

11%. After adjustment for socioeconomic factors, low birth weight and maternal smoking before and

during pregnancy, a dose-response relationship with exposure to secondhand tobacco smoke was

observed regarding hyperactivity ⁄ inattention (odds ratio compared to ‘none’ was 1.35 for ‘low ⁄medium’ and 2.39 for ‘high’ exposure, 95% confidence intervals 1.02–1.78 and 1.62–3.53,

respectively) as well as for conduct problems (OR 1.68 (1.37–2.06) and 1.93 (1.39–2.68)).

Conclusion: Secondhand tobacco smoke exposure at home appears to be associated with an increased risk of

behavioural problems among preschool children. Prevention of behavioural problems may be a further reason

to target secondhand tobacco smoke exposure in children.

INTRODUCTIONThe consequences of exposure to secondhand tobaccosmoke for the foetus and the child have been widelydescribed (1–3). These include a number of physical symp-toms and diseases such as the sudden infant death syn-drome and respiratory effects. In addition, a large body ofliterature is available on children whose mothers smokedduring pregnancy and this literature consistently demon-strates that such children have higher rates of behavioural

problems than those not exposed (4–9). However, muchless is known about the potential role of postnatal exposureto secondhand tobacco smoke for the development ofbehavioural problems in children.

The isolation of the independent effect of postnatal expo-sure to secondhand tobacco smoke on child behaviour ishindered by the correlation between prenatal and postnatalexposure. Furthermore, exposure to secondhand tobaccosmoke of the child is correlated with other factors that mayadversely affect behavioural outcomes in children such aslow maternal education and low socioeconomic status ofthe family. However, for policy implications, it is importantto know whether the behavioural effects associated withexposure to secondhand tobacco smoke are because of pre-natal or early childhood secondhand tobacco exposure orboth prenatal and postnatal exposure (5,6). The aim of ourstudy thus was to assess the association between postnatalsecondhand tobacco smoke exposure and childhood beha-viour taking possible confounding effects of prenatalsecondhand tobacco exposure as well as other potential riskfactors into account.

PARTICIPANTS AND METHODSAnalyses are based on a large survey among preschool chil-dren conducted in Bavaria, Germany, in 2005–2006 (10).

GME Study Group: Bavarian Health and Food Safety Authority,Oberschleissheim (Gabriele Bolte, Hermann Fromme, AnnetteHeissenhuber, Christine Mitschek, Michael Mosetter, Uta Nenn-stiel-Ratzel, Manfred Wildner); Health Authority of the DistrictOffice of Bamberg (Winfried Strauch, Rosemarie Sittig, HeidiThamm); Health Authority of the District Office of Guenzburg(Roland Schmid, Tatjana Fries-Hesse, Gudrun Winter); HealthAuthority of the City Ingolstadt (Elisabeth Schneider, TraudlTontsch, Christine Gampenrieder, Margot Motzet, Gerline Woelk);Department of Health and Environment, City of Munich (HeidiMayrhofer, Sylvia Kranebitter, Gertraud Rohrhirsch); HealthAuthority of the District Office of Schwanburg (Maximilian Kueh-nel, Kornelia Baranek, Gitte Koch-Singer); Institute of Social Pedi-atrics and Adolescent Medicine, Ludwig-Maximilian-UniversityMunich (Ruediger von Kries, Ladan Baghi); Bavarian State Minis-try of the Environment and Public Health (Bernhard Liebl)

Acta Pædiatrica ISSN 0803–5253

106 ª2009 The Author(s)/Journal Compilation ª2009 Foundation Acta Pædiatrica/Acta Pædiatrica 2010 99, pp. 106–111

Data collection was coupled to the compulsory preschoolexamination, which all children in Bavaria have to undergobefore entering school. All children were eligible who tookpart at this compulsory examination prior to school enrol-ment for the school year 2006 ⁄ 2007 in three selected citiesand three counties. Children were mostly five or six years ofage. Informed consent was obtained from parents. The sur-vey was approved by the Ethical Committee of the BavarianChamber of Physicians.

Data collectionData were collected via a questionnaire, which had to befilled out by a parent and which included questions on socio-demographic factors, environmental exposures, living condi-tions, health behaviours and health outcomes of the child.Detailed information on exposure to secondhand tobaccosmoke of the child was collected and the Strengths andDifficulties Questionnaire (SDQ P4–16), which is a briefquestionnaire to screen for child psychiatric disorders incommunity samples, was applied (11).

Data on smoking in the child’s home were used to catego-rize postnatal secondhand tobacco smoke exposure of thechild. Exposure was considered ‘high’ if at least one personsmoked regularly (at least 1 cigarette ⁄ day) indoors and inthe presence of the child. It was considered ‘medium’ ifsomebody in the home smoked on a regular basis, but smok-ing was restricted to the terrace or balcony or not in thepresence of the child. If only occasional smoking in thehome was reported, exposure was categorized ‘low’, and fora non-smoking household, exposure was categorized ‘no’. Ifsomebody smoked in the household, it was recordedwhether this was the mother, the father or somebody else.Questions were related to the current situation in the house-hold. Data on smoking of the mother before and duringpregnancy were collected retrospectively.

The 25 items of the SDQ were summarized to the fourproblem subscales ‘emotional symptoms’, ‘conduct prob-lems’, ‘hyperactivity ⁄ inattention’, and ‘peer relationshipproblems’ and the strength subscale ‘prosocial behaviour’.The four problem subscales were then added to generatethe ‘total difficulty score’. Depending on the score, prob-lems were categorized as ‘unlikely’, ‘possible’ and ‘proba-ble’ with respect to each subscale as well as the overallscore (11).

Statistical analysesThe prevalence of the behavioural problems was deter-mined for boys and girls separately and differences betweenthe genders were tested with the Mantel-Haenszel v2. Cor-relations between the different exposures, outcomes, andsociodemographic factors were estimated by the Kendalls s-b in case of ordinal variables and with Cramers V in case ofnominal variables. Being occupied for <15 h per week wasconsidered ‘minor employment’. Crowding was defined as<20 m2 living space per person or more than one person perroom. The household equivalent income was calculated byweighting the monthly household net income as disposableincome after taxes and social transfers according to age and

number of household members using the weighting factorsof the OECD scale (12). As threshold of poverty risk, 60%of the regional median income per survey was defined. As asignificant proportion (42%) of parents refused to indicatetheir household net income, a separate category ‘refusal ormissing’ was used in the analyses. Parental education wasdefined as the highest level of completed educationachieved by mother or father using the categories ‘very high’(at least undergraduate studies), ‘high’ (general qualificationfor university entrance but no completed study), ‘middle’(upper secondary school certificate) and ‘low’ (lower sec-ondary school certificate or no graduation).

The association of exposure to secondhand tobaccosmoke with behavioural problems was estimated in logisticregression models comparing the problems ‘probable’ groupwith the combined group of problems ‘unlikely’ and ‘possi-ble’. As risk estimators were almost identical, the ‘low’ and‘medium’ exposure groups were combined.

The association was first determined using bivariate ana-lysis (model 1). To control for alternative explanations forthe observed association, multivariate analysis was con-ducted. First, in model 2, those socioeconomic factors thatshowed a significant (p < 0.05) association with at least oneof the behavioural subscales (Mantel-Haenszel v2 for ordi-nal and Pearsons v2 for nominal variables) were selected. Toreduce multicollinearity, only a selection of the thus identi-fied socioeconomic variables were included in model 2: thestudy area and foreign nationality, both being related tocrowding, single parent, which is closely related to familysize and employment status of the mother, parental educa-tion and relative poverty. The number of fathers being notemployed was low, particularly in the subgroups of behavio-ural problems and hence this variable was not considered inthe model. Age did not turn out to be a predictor for any ofthe behavioural subscales. In addition, gender and low birthweight (<2500 g, no vs yes) were included. If birth weightwas missing, low birth weight was coded as ‘yes’ in case of apremature birth and ‘no’ in case of a normal birth. Secondly,in model 3, the smoking status of the mother before andduring pregnancy was added. Multicollinearity was assessedin model 3 excluding the variable poverty (as it is not ordi-nal) by the variance inflation factor VIF (with values above2.5 considered indicative).

To assess possible interaction, in addition, analyses strati-fied by gender and analyses stratified by maternal smokingduring pregnancy were conducted.

All statistical computations were performed using SASstatistical software, release 9.1. (SAS Institute Inc., Cary,NC, USA).

RESULTSOverall, data of 6206 children were collected (response rate73%). Of those, 321 had to be deleted from analyses becauseof missing data on exposure to secondhand tobacco smoke(n missing mother smoked before pregnancy = 152, n miss-ing mother smoked during pregnancy = 141, n missingpostnatal exposure of the child = 28), 36 because of

Twardella et al. Exposure to secondhand tobacco smoke and child behaviour

ª2009 The Author(s)/Journal Compilation ª2009 Foundation Acta Pædiatrica/Acta Pædiatrica 2010 99, pp. 106–111 107

implausible information (mother did not smoke beforebut during pregnancy) and 355 because of missing dataon psychiatric scores, leaving 5494 subjects for analyses.A description of the study population is given in Table S1in Supplemental Material online. Apart from fewexceptions, the children were between five and seven yearsof age.

Before pregnancy, 972 mothers (17.7%) smoked ciga-rettes, 447 of whom (8.1% of the total population) contin-ued smoking during pregnancy (Table S2 in SupplementalMaterial online). After birth, 70% of children were notexposed to any secondhand tobacco smoke at home. In11%, exposure was low, in 13%, medium and in 7%, high.Postnatal exposure to secondhand tobacco smoke of thechild was correlated with smoking of the mother before(r = 0.39, p < 0.0001) and during pregnancy (r = 0.34,<0.0001).

Indications for psychological problems were observed in11–25% of the children. Most frequently, conduct problemswere observed (14% possible, 11% probable), least frequentwere hyperactivity ⁄ inattention (4% possible, 6% probable)(Table S3 in Supplemental Material online). Girls were sig-nificantly less frequently affected by conduct problems,hyperactivity ⁄ inattention and peer relationship problems aswell as by an indicative total difficulty score. Deficiencies inprosocial behaviour were found in 6% (possible) and 3%(probable) of the children, again with lower prevalence ingirls than in boys.

In bivariate analysis, a significant increase in risk withincreasing secondhand tobacco smoke exposure for theproblem subscales ‘conduct problems’, ‘hyperactivity ⁄ inat-tention’, and ‘peer relationship problems’, as well as the‘total difficulty score’ was observed, suggesting a dose-response relationship (Table 1). The inclusion of socioeco-nomic variables (model 2) as well as smoking status of themother before and during pregnancy (model 3) reduced theodds ratios. A dose-response relationship was seen only for‘hyperactivity ⁄ inattention’: the odds ratio (OR) comparingthe low ⁄ medium exposure group with the no exposuregroup was 1.35 (95% confidence interval CI 1.02–1.78) theOR for the high exposure group 2.39 (95% CI 1.62–3.53).For ‘conduct problems’, the odds ratio of the high exposuregroup compared to no exposure (OR = 1.93, 95% CI 1.39–2.68) is only slightly higher than the odds ratio comparingthe low ⁄ medium group to the no exposure group(OR = 1.68, 95% CI 1.37–2.06) and the confidence inter-vals are widely overlapping. For ‘peer relationship prob-lems’ and ‘total difficulty score’, the risk increase in thelow ⁄ medium and high exposure group is only small and notconsistently significant.

For the problem subscale ‘emotional problems’, no cleardose-response pattern could be observed. Regarding thepositive subscale ‘prosocial behaviour’, no significant asso-ciation with postnatal exposure to secondhand tobaccosmoke could be observed. All VIF were low with the highestvalue being 1.8.

Table 1 Association of exposure to secondhand tobacco smoke with behavioural problems

Secondhand tobaccosmoke exposure

Unlikely ⁄ possible probable

Bivariate OR (95% CI) Model 2†

OR (95% CI) Model 3† OR (95% CI)N (%) N (%)

Emotional problems

None 3624 (94.7) 202 (5.3) 1.00 1.00 1.00

Low ⁄ Medium 1194 (91.8) 107 (8.2) 1.61 (1.26, 2.05) 1.47 (1.14, 1.89) 1.44 (1.10, 1.88)

High 340 (92.6) 27 (7.4) 1.43 (0.94, 2.16) 1.13 (0.72, 1.77) 1.04 (0.64, 1.69)

Conduct problems

None 3487 (91.1) 339 (8.9) 1.00 1.00 1.00

Low ⁄ Medium 1094 (84.1) 207 (15.9) 1.95 (1.62, 2.34) 1.76 (1.45, 2.14) 1.68 (1.37, 2.06)

High 286 (77.9) 81 (22.1) 2.91 (2.22, 3.82) 2.17 (1.61, 2.93) 1.93 (1.39, 2.68)

Hyperactivity ⁄ Inattention

None 3641 (95.2) 185 (4.8) 1.00 1.00 1.00

Low ⁄ Medium 1197 (92.0) 104 (8.0) 1.71 (1.33, 2.19) 1.57 (1.21, 2.03) 1.35 (1.02, 1.78)

High 311 (84.7) 56 (15.3) 3.54 (2.57, 4.88) 3.15 (2.22, 4.47) 2.39 (1.62, 3.53)

Peer relationship problems

None 3541 (92.6) 285 (7.5) 1.00 1.00 1.00

Low ⁄ Medium 1161 (89.2) 140 (10.8) 1.50 (1.21, 1.85) 1.22 (0.97, 1.53) 1.26 (0.99, 1.59)

High 316 (86.1) 51 (13.9) 2.01 (1.46, 2.76) 1.30 (0.92, 1.86) 1.38 (0.94, 2.01)

Total difficulty score

None 3686 (96.3) 140 (3.7) 1.00 1.00 1.00

Low ⁄ Medium 1225 (94.2) 76 (5.8) 1.63 (1.23, 2.18) 1.30 (0.96, 1.76) 1.29 (0.94, 1.77)

High 333 (90.7) 34 (9.3) 2.69 (1.82, 3.98) 1.46 (0.93, 2.29) 1.40 (0.86, 2.29)

Prosocial behaviour

None 3731 (97.5) 95 (2.5) 1.00 1.00 1.00

Low ⁄ Medium 1256 (96.5) 45 (3.5) 1.41 (0.98, 2.02) 1.32 (0.91, 1.92) 1.32 (0.89, 1.96)

High 355 (96.7) 12 (3.3) 1.33 (0.72, 2.44) 1.11 (0.58, 2.11) 1.13 (0.57, 2.34)

†Besides the secondhand tobacco smoke exposure, the following variables are included in the model: model 2: gender, area, foreign nationality, single parent,

parental education, relative poverty, low birth weight; model 3: in addition, smoking of the mother before and during pregnancy.

Exposure to secondhand tobacco smoke and child behaviour Twardella et al.


In analyses stratified by gender, associations were similarfor boys and girls except for ‘peer relationship problems’and ‘prosocial behaviour’ (Table S4 in SupplementaryMaterial online): among boys no association was observed,but among girls, a significantly increased risk of deficienciesin ‘prosocial behaviour’ was found in the low ⁄ mediumexposure group and a dose-response relationship foundwith respect to ‘peer relationship problems’. In analysesstratified by maternal smoking during pregnancy, oddsratios were somehow different between strata, but confi-dence intervals were widely overlapping.

DISCUSSIONIn a large population of preschool children in Bavaria, weobserved a significant increase in risk of behavioural prob-lems with increasing postnatal secondhand tobacco smokeexposure. A dose-response pattern was particularly clearwith respect to ‘hyperactivity ⁄ inattention’ and the associa-tion furthermore strong with respect to ‘conduct problems’.These associations remained after consideration of socio-economic factors, low birth weight and smoking of themother before and during pregnancy in analysis. For thesubscales ‘peer relationship problems’ and ‘prosocial beha-viour’, an association with exposure to secondhand tobaccosmoke was found only in girls, but not in boys. No clear pat-tern could be observed for emotional problems. There areno indications for differential associations depending onmaternal smoking during pregnancy.

The relationship between postnatal secondhand tobaccosmoke exposure of the child and behavioural problems ta-king maternal smoking during pregnancy into account hasbeen studied in five studies so far. In the first study including2251 children aged 4 to 11 years in 1986, an increase in thenumber of behavioural problems was observed in childrenwhose mothers smoked after but not during pregnancy incomparison with non-smoking mothers (13). In addition,after adjusting for a number of socioeconomic factors,mothers’ health and alcohol abuse, subscale scores for ‘anti-social behaviour’, ‘anxious ⁄ depressed’, ‘headstrong’, ‘hyper-active’ and ‘immature’ were significantly increased in thesechildren. These results could not be replicated in the secondstudy in which the prevalence of conduct disorders, atten-tion deficit and total disruptive behaviour was assessed in1200 children at age 8, 10 and 12 years (14). While smokingduring pregnancy was associated with significant increasesin child disruptive behaviours, smoking after pregnancy wasnot associated with these behaviours in analysis adjusted forconfounders and maternal smoking during pregnancy. In athird study, 4879 mothers provided data on child behaviourwhen children were 5 years old (internalizing, externalizingand ‘social, attentional thought’) (15). In multivariate analy-sis externalizing behaviour was significantly associated withmaternal smoking in early pregnancy as well as after preg-nancy. Children of mothers who were smoking when thechild was 5 years had increased rates of externalizing childbehaviour problems even if the mother had never smokeduntil after the birth of their infant.

The validity of these three studies is limited, becausematernal smoking was used as a proxy for children’s sec-ondhand tobacco smoke exposure, which might both resultin an overestimation or an underestimation of exposure. Inour study, in only 606 of the 1038 households in which reg-ular smoking took place, the mother was reported to smokeregularly at home.

This limitation does not pertain to the fourth study, whichused ‘anyone living at the child’s home smokes cigarettes,cigars or pipes anywhere inside this home’ to describe thechild’s postnatal secondhand tobacco smoke exposure, adefinition very similar to that of ours (16). This study was ananalysis of NHANES data 1999–2002, a cross-sectional sur-vey in the USA with 3879 children aged 4–15 yearsincluded in multivariate analyses. The outcome was definedby the diagnosis of ADHD (Attention Deficit HyperactivityDisorder) by a physician and current use of stimulant medi-cation. While maternal smoking during pregnancy was asignificant predictor of ADHD diagnosis, the presence of asmoker in the home was not.

However, this study is limited as well due to the chosenoutcome. Studies relying on caregiver reports of an ADHDdiagnosis might reflect differential access to health care ordiagnostic bias. In fact, this has been shown among 8–15 year old children taking part in NHANES 2001–2004:When DSM-IV criteria were applied, the poorest childrenwere most likely to fulfil criteria for ADHD, but less likelythan wealthy children to receive regular medication treat-ment (17). Among those meeting DSM-IV criteria, only48% of caregivers reported that their child had received anADHD diagnosis by a health professional. The proportionwas the lowest in the poorest category, but not significantlydifferent from that in the wealthier category.

Eventually, in the fifth study, an analysis based onNHANES data 2001–2004 on children aged 8–15 yearswas conducted (18). Serum cotinine levels were used todetermine children’s exposure to secondhand tobaccosmoke and caregivers’ interview data were used to assessthe presence of conduct disorders based on DSM-IV crite-ria. In the analysis adjusted for child’s age, child’s gender,poverty-to-income-ratio, child’s race, maternal age at child’sbirth, prenatal tobacco exposure and blood lead levels, thecotinine level was associated with the presence of conductdisorders (e.g. OR comparing fifth quintile with first quintile9.15, 95% confidence interval 1.47 to 56.90).

In our study, associations were particularly strong withrespect to ‘hyperactivity ⁄ inattention’ and ‘conduct prob-lems’. This is in agreement with the literature on effects ofsmoke exposure during pregnancy, which appears to showan effect specific for externalizing problems, but not forinternalizing problems (8,19,20) as well as with the study ofWilliams et al. (15), which found effects of pre- and postna-tal exposure on externalizing behaviour only. The strongdose-response relationship of secondhand tobacco smokeexposure and ‘peer relationship problems’ in girls needs tobe further analysed. Our data do not support the hypothesis,that associations are dependent on smoking during preg-nancy. In fact, in model 3, which included both secondhand



tobacco smoke exposure as well as maternal smoking dur-ing pregnancy, we could not find any significant associationbetween maternal smoking during pregnancy and any of thebehavioural outcomes. Thus, the prevention of secondhandtobacco smoke exposure in children is of equal importancein those already exposed in utero and in those not.

In our study, we achieved a high sample size and a gooddata quality by use of a well-established questionnaire.While we observed an association between postnatal se-condhand tobacco smoke exposure and psychologicalsymptoms, the causality of the association is hard to prove.Residual confounding, particularly because of familialbehaviour problems, may serve as an explanation for theobserved relationship. Mothers who smoke during preg-nancy have been found to be more likely to show antisocialbehaviour, to have children with men showing antisocialbehaviour and were more likely to have depression (21). Ina large twin study, it has been shown that the associationbetween prenatal smoking and childhood conduct prob-lems is heavily confounded by other known risks for chil-dren’s behavioural development, i.e. genetic factors,maternal and paternal antisocial behaviour and maternaldepression (21). Recently, in a study of more than 2000 sib-ling sets, it was shown that the association between mater-nal smoking and conduct problems in children waseliminated when an analysis conditional on family was used(22). The authors argued that in conditional analysis,known and unknown risk factors pertaining to the familysituation, including social, environmental and psychiatricfactors, are accounted for. As we have not collected infor-mation on the family situation or on maternal mentalhealth, we were not able to adjust for these factors in ouranalysis. Thus, the effect of exposure to secondhandtobacco smoke would be difficult to distinguish from abroader range of familial factors associated with maternalsmoking. Some of these familial factors we were able toaccount for in our study, particularly socioeconomic factors.And while we did adjust for maternal smoking, we mighthave reduced confounding by its correlates indirectly. How-ever, residual confounding by further familial factors cannotentirely be ruled out.

Data on prenatal and current exposure of the child arebased on self-report of the parents only. However, parentalself-report of children’s secondhand tobacco smoke expo-sure has been shown to be well correlated with serum coti-nine levels of the child (23) as well as nicotine exposure inthe air (24).

As yet, the biological mechanism underlying a possiblecausal relationship between secondhand tobacco smokeexposure during early childhood and compromised physicaland cognitive development in children has not beenexplained. Biological evidence for an alteration of braindevelopment because of postnatal secondhand tobaccosmoke exposure, however, was found in an experimentalstudy in rats (25). In this study, rats were exposed to sidestream smoke in utero (side stream smoke exposure of thepregnant mother) and ⁄ or postnatal. While in utero expo-sure had no effect on three brain parameters analysed

(DNA, protein and cholesterol concentrations), postnatalside stream smoke exposure reduced hindbrain DNA con-centration (an indicator of cellular density) and increasedthe hindbrain protein ⁄ DNA ratio (an indicator of cell size).More investigations into the role of postnatal secondhandtobacco smoke exposure in neurodevelopment are neces-sary.

Smoking during pregnancy is generally considered therelevant exposure based on what is known about biologicalmechanisms and results from other studies. However, ourfindings support the hypothesis of an effect of postnatalsmoking independent of maternal smoking during preg-nancy. In our cross-sectional study, exposure to second-hand tobacco smoke at home was associated with anincreased risk of behavioural problems among preschoolchildren even after taking socioeconomic factors and mater-nal smoking during pregnancy into account. The preventionof behavioural problems may thus be a further reason to tar-get secondhand tobacco smoke exposure in children.

ACKNOWLEDGEMENTThis work was supported by the Bavarian State Ministry ofthe Environment and Public Health.

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SUPPORTING INFORMATIONAdditional Supporting Information may be found in theonline version of this article:

Table S1 Description of the study population and compari-son with children excluded from analyses.Table S2 Exposure to exposure to secondhand tobaccosmoke in 5494 preschool children in Bavaria.Table S3 Prevalence of behavioural problems in 5494 pre-school children in Bavaria, overall and gender-specific.Table S4 Results of stratified analysis: odds ratios for low ⁄medium and high secondhand tobacco smoke exposure incomparison to no exposure stratified by gender and strati-fied by maternal smoking during pregnancy.

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Exposure to secondhand tobacco smoke and child behaviour – results from a cross-sectional study among preschool children in Bavaria