The association between passive and active tobacco smoke

exposure and child weight status among Spanish children

Oliver Robinson1,2,3, David Martínez1,2,3, Juan J Aurrekoetxea4,5,6, Marisa Estarlich3,7, Ana

Fernández Somoano3,8, Carmen Íñiguez7,3, Loreto Santa-Marina4,5,6, Adonina Tardón3,8, Maties

Torrent9, Jordi Sunyer1,2,3 Damaskini Valvi1,2,3,10 and Martine Vrijheid*1,2,3

1. ISGlobal, Centre for Research in Environmental Epidemiology (CREAL)2. Universitat Pompeu Fabra (UPF)3. CIBER Epidemiología y Salud Pública (CIBERESP)4. Public Health Department, Basque Government, Spain5. University of the Basque Country (UPV/EHU), Spain;6. Health Research Institute (BIODONOSTIA), Spain7. Epidemiology and Environmental Health Joint Research Unit, FISABIO–Universitat

Jaume I–Universitat de València, Spain8. Department of Medicine, University of Oviedo, Spain9. Ib-salut, Area de Salut de Menorca, Spain10. Department of Environmental Health, Harvard T.H. Chan School of Public Health,

United States

Key words: Passive smoking, second hand smoke, overweight, obesity, cotinine

RUNNING TITLE: Passive tobacco smoke exposure and child BMI

*Corresponding author: mvrijheid@creal.cat

Parc Recerca Biomèdica de Barcelona, Doctor Aiguader, 88,

08003 Barcelona, Spain

Word count: 3,599

The authors have no potential or actual conflicts of interests to disclose, financial or otherwise.

1

FUNDING:

This study was funded by grants from Instituto de Salud Carlos III (Red INMA G03/176 and CB06/02/0041), Spanish Ministry of Health (FIS-97/1102, FIS-07/0252, FIS-PS09/00362, 97/0588, 00/0021-2, PI061756, PS0901958, PI14/00677 incl.FEDER funds, FIS-PS09/00090, PI041436, FIS-PI042018, FIS-PI06/0867, PI081151 incl. FEDER funds, FIS-PI09/02311 and FIS-PI13/02187, and FIS-FEDER 03/1615, 04/1509, 04/1112, 04/1931, 05/1079, 05/1052, 06/1213, 07/0314, 09/02647, 11/01007, 11/0178, 11/02591, 11/02038, PI12/01890 incl. FEDER funds, 13/1944, 13/2032, FIS-PI13/02429, 14/0891, 14/1687 and CP13/00054 incl. FEDER funds), Spanish Ministry of Economy and Competitiveness (SAF2012-32991 incl. FEDER funds), CIBERESP, Generalitat de Catalunya-CIRIT 1999SGR 00241, Generalitat de Catalunya-AGAUR (2009 SGR 501, 2014 SGR 822), the Conselleria de Sanitat Generalitat Valenciana, Department of Health of the Basque Government (2005111093, 2009111069 and 2013111089), the Provincial Government of Gipuzkoa (DFG06/004 and DFG08/001), Fundació La Caixa (97/009-00 and 00/077-00), Beca de la IV convocatoria de Ayudas a la Investigación en Enfermedades Neurodegenerativas de La Caixa, Fundació La marató de TV3 (090430), Obra Social Cajastur/Fundación Liberbank, Universidad de Oviedo, the EU Commission (QLK4-1999-01422, QLK4-CT-2000-00263, QLK4-2002-00603, CONTAMED FP7-ENV-212502, FP7-ENV-2011 cod 282957, HEALTH.2010.2.4.5-1, 261357, 308333, 603794), Agence Nationale de Securite Sanitaire de l'Alimentation de l'Environnement et du Travail (1262C0010), Consejería de Salud de la Junta de Andalucía (grant number 183/07) and Annual agreements with municipalities in the study area (Zumarraga, Urretxu, Legazpi, Azkoitia y Azpeitia y Beasain).

What is already known about this subject?

-The epidemiological literature consistently shows an association with maternal active smoking and child risk of overweight / obesity.

-The majority of animal studies have shown that rats exposed to nicotine during perinatal development gained more fat mass and body weight than controls

-Only a handful of studies has assessed the effects of passive smoking, either prenatally or by the child postnatally

What does your study add?

-Our study directly addresses both passive smoke exposure by the mother prenatally and in the early life of the child.

-Our study adds corroboration of tobacco smoke exposure with biomarker measurements at both time points and additional detailed assessments of a wide range of socio-demographic, dietary and physical activity covariates.

-We follow children up to the age of 14 years in a subcohort analysis, the oldest yet in studies of passive smoking.

2

AbstractObjective: To assess the impact of passive and active tobacco smoke exposure, both pre- and postnatally, on child body mass index (BMI) and overweight.

Methods: Pregnant women were enrolled into the Spanish INMA prospective birth cohort during 1997-2008. Tobacco smoke exposure was assessed by questionnaire and corroborated by pre- and postnatal cotinine measurements. Children were followed up until 4 years in newer subcohorts (N=1866) and until 14 years in one older subcohort (N=427). Child age and sex specific BMI z-scores were calculated and generalized estimating equations were used to model their relationship with repeated measures of tobacco smoke exposure.

Results: We observed associations between prenatal passive exposure to tobacco smoke (adjusted β= 0.15, 95% C.I.: 0.05, 0.25) and active maternal smoking (adjusted β= 0.20, 95% C.I.: 0.08, 0.33) and child zBMI up to 4 years. Stronger associations were observed in the older subcohort between both prenatal and child passive smoke exposure and zBMI up to 14 years.

Conclusions: We have provided evidence for an effect of both passive and maternal active smoking on child postnatal growth. Although residual confounding cannot be completely ruled out, associations were robust to adjustment for a range of lifestyle factors.

3

IntroductionThe prevalence of childhood obesity has increased worldwide during the past few decades (1),

and while it is primarily caused by a greater intake of energy than is expended (2), it is

hypothesized that environmental chemical exposures, particularly in utero, may influence

metabolic programming and increase an individual’s susceptibility to obesity (3). Maternal

active smoking during pregnancy is a well documented example of a chemical “obesogen” and

has been associated with childhood obesity in several studies with meta-analyses estimating

odds ratios of around 1.5 for this association (4, 5). Furthermore the majority of animal studies

have shown that rats exposed to nicotine during perinatal development gained more fat mass

and body weight than controls (6). Although unmeasured residual confounding may contribute

to the association observed in human studies, the consistency of the epidemiological evidence

taken together with the toxicological data suggest a causal relationship (6).

Less is known about the association with passive or second hand exposure to tobacco smoke

both by the mother during pregnancy and directly by the child during early life. Only a few

studies have assessed the association between direct measures, through questionnaire or

biomarker, of maternal prenatal passive smoke exposure and child weight status, with

inconsistent results (7, 8, 9). More studies have assessed the effect of partner smoking during

pregnancy, with the majority finding a positive association with child body mass index (BMI)

(9, 10, 11, 12, 13). However there is disagreement regarding whether these effects reflect

residual confounding by familial factors, a biological causal effect due to passive smoke

exposure, or a mixture of both. A handful of studies have investigated the effects of postnatal

child passive smoke exposure and child BMI (9, 12, 14, 15, 16). While the majority of these

studies reported an association with parental reported levels of child exposure, no previous

study has employed biomarker measurements in the child to strengthen the exposure

classification.

In this study of mother-child pairs in the Spanish INMA ( Environment and Childhood)

population-based birth cohort, we present an analysis of the effect of maternal active and

passive smoke exposure during pregnancy and child passive smoke exposure on child weight

status. In a substantial number of mother-child pairs, we have employed both questionnaire and

biomarker based indicators of exposure along with extensive information on lifestyle and

demographic factors, to investigate the effects on child early growth pattern and repeated child

BMI measures up to 4 years. Furthermore in a analysis of an older INMA subcohort, we have

tracked the effect on BMI of children right up to 14 years of age.

4

Methods

SubjectsThe INMA birth cohort was established between 2003 and 2008 in the four "new" regional

subcohorts of Asturias, Gipuzkoa, Sabadell and Valencia, and between 1997 and 1998 in the

older Menorca subcohort (17). A total of 3,174 eligible women were recruited during their

routine antenatal examination at the first trimester of pregnancy. To be included women had to

be at least 16 years old, intend to deliver in the reference hospital, have a singleton pregnancy

with no assisted conception, and have no problems with communication. The study was

conducted with the approval of the hospital and institutional ethics committees, and written

informed consent was obtained from all women.

Exposure and covariate information

Questionnaires were administered by trained interviewers twice during pregnancy (at around 12

and 32 weeks of pregnancy) and at child ages of around 1 and 4 years. Information on physical

activity was used to compute overall metabolic equivalent of tasks (METs) levels (19). Maternal

diet was assessed through a validated food frequency questionnaire in the new sub cohorts,

repeated twice during pregnancy (20). Child diet was assessed at 4 years of age through a

similar questionnaire. Maternal pre-pregnancy BMI was calculated from reported pre-pregnancy

weight and measured height at the first visit.

Tobacco smoke exposure categories were constructed from participant responses to a detailed

smoking questionnaire (21) (22) repeated twice during pregnancy and the 1 and 4 year

postnatal follow-up points. In the prenatal period the categories were: 1. "Non smoker" (non-

smoker at beginning of and during pregnancy with no reported passive exposure to tobacco

smoke); 2. "Passive smoker" (Non-smoker at beginning of and during pregnancy with reported

passive exposure to tobacco smoke at home, work or other regularly visited place); 3. "Partial

smoker" (Smoker at beginning of pregnancy or at 12 weeks, who had reported stopping

smoking by the 32 week interview); 4. "Active smoker" (reported being a smoker at the 32

week interview). The postnatal exposure variables were constructed using the current smoking

statuses of the parents at the family home as a proxy of child passive exposure to tobacco

smoke: 1. No parent of the child smokes at home; 2. One of the parents of the child smokes at

home; 3. Both parents of the child smoke at home. These exposure categories were compared

with cotinine measurements made in urine samples collected from the mothers at the 32 week

visit and from the children at the 4 year follow-up in the new sub cohorts. Cotinine, an

established biomarker of recent tobacco exposure, was measured by competitive enzyme

5

immunoassay as previously described (21) (22){Aurrekoetxea, 2016 #62}{Aurrekoetxea, 2016

#62}. Values below the limit of detection (LOD, 4 ng/mL) were replaced by 2 ng/mL.

Outcome assessmentChild weight and height were measured at each follow-up visit using standard protocols,

without shoes and in light clothing. We calculated BMI (weight/height2) and used the WHO

reference curves to estimate age- and sex-specific BMI Z-scores (zBMI) (23). Overweight was

defined as a zBMI ≥ the 85th percentile. Children were defined as rapid or normal growers in

the first six months of life using repeat weight measurements extracted from their medical

records, with those children with a difference between birth and 6 month weight Z-scores

greater than 0.67 standard deviations from the mean considered rapid growers (24).

Statistical analysesWe assessed the four new INMA subcohorts together in a pooled analysis and the older

Menorca subcohort in a separate analysis. We assessed the association between tobacco smoke

exposure and child weight status up to 4 years in the pooled analysis and up to 14 years in the

Menorca analysis. In the pooled analysis, to incorporate both repeated measures of child weight

status and postnatal exposure status (assessed at 1 and 4 years)., we used generalised estimating

equations (GEE) with an unstructured correlation matrix and a Gaussian or binomial

distribution specification (for continuous and dichotomous outcomes, respectively). Since in

the Menorca subcohort analysis, we had more repeat measurement points of outcome than

exposure, GEE was used only to model the outcome data (assessed at 4, 6, 11 and 14 years),

with postnatal tobacco smoke exposure assessed at the 4 years time point only. In the pooled

analysis, we assessed rapid growth using logistic regression.

Basic and fully adjusted models were adjusted for child sex and with an indicator variable for

subcohort in the pooled analyses. Additional potential covariates for inclusion in fully adjusted

models were selected from the literature (14). The variables considered in both the pooled and

Menorca subcohort analyses were socio-economic status (paternal occupation class and

education, maternal occupation class and education), maternal country of origin (Spanish,

other), maternal age, maternal BMI, breastfeeding (ever breastfeeding and breastfeeding

duration) and child physical and sedentary activity at 4 years (hours/week spent sleeping,

watching TV and engaging in sedentary activities; total METs expended over week during

commute to school, during sedentary activities, during physical activities in and outside the

school). In the pooled analyses, we additionally examined paternal BMI, maternal physical

activity (average total METs/week), maternal alcohol consumption, and maternal and child diet

(daily averages over pregnancy and at child age 4 years including total calories, total fat, total

proteins, total carbohydrates, total fruit, total vegetables and total sugar consumption). Those

6

covariates significantly ( p < 0.05) related in bivariate testing to both exposure (χ2 or ANOVA

tests), and outcome (χ2 or Pearson's correlations) , in addition to maternal and paternal BMI and

education, were then considered for inclusion in the final model. To prevent over-fitting, only

those covariates that modified the exposure coefficient by ≥ 10% following forward stepwise

procedure were retained. To address the potential bias and loss of precision that could result

from incomplete case analyses, we used multiple imputations to replace missing values in

covariates (table 1). We created 20 imputations, generating 20 complete datasets that we

analyzed following the standard combination rules for multiple imputations (25). Results using

the complete case dataset are provided for comparison with imputed results in supplementary

tables s6 and s7.

Further analyses included sensitivity analyses where children born prematurely (< 37 weeks

gestational age) and with birth weight below 2500g were excluded. To test the robustness of our

results we also stratified by child sex, maternal BMI and maternal social class. Interactions

between tobacco smoke exposure and stratification variables was assessed by likelihood ratio

tests.. All analyses were conducted with Stata 12.0 statistical software (Stata

Corporation,College Station, TX).

ResultsAfter excluding women who withdrew, were lost to follow-up, or underwent abortions or fetal

deaths, 2644 pregnant women in the new subcohorts and 443 in the Menorca subcohort were

monitored through delivery. Final analyses included 1927 children with exposure and outcome

data up to 4 years in the new subcohorts (72% of those followed to birth) and 427 children

followed until 14 years in the Menorca sub cohort (96% of those followed to birth) . Women

lost to follow-up by the time the child was aged 1.5 years were more likely to be of lower social

class and have smoked at any time during pregnancy (17).

Mothers who were not prenatally exposed to tobacco smoke were on average better educated

and of higher occupational social class, had lower pre-pregnancy BMI, and consumed less total

calories, fat and alcohol and more vegetables and fruits during pregnancy than mothers who

were exposed to tobacco smoke (tables 1 and 2). The children of non-exposed mothers had

higher birth weight, breastfed for longer and tended to sleep for longer, spend less time

watching television, and consume less calories, fat and sugar and more fruit at four years of age

(tables 1 and 2). Maternal and paternal BMI and child birth weight were all positively

associated with zBMI of the child at 4 years (all p < 0.001) (supplementary tables 1 and 2).

7

Boys and children who consumed more fruit and total sugar and watched more television at 4

years also had higher zBMI scores at 4 years (tables s2 and s3).

New subcohorts analysisIn the new INMA sub cohorts in Asturias, Gipuzkoa, Sabadell and Valencia, 697 (36%) of

mothers were non-smokers, 571 (30%) were passive smokers, 317 (16%) were "partial

smokers" and 342 (18%) were active smokers throughout pregnancy. At 4 years, 1289 (79%)

children had no parents who smoked at home, 209 (13%) had one parent who smoked at home

and 140 (9%) had two parents who smoked at home. These ordinal categories from

questionnaire data were significantly related to respective urinary cotinine levels in the mother

at 32 weeks of pregnancy (p < 0.001) and in the child at 4 years (p < 0.001) (figure 1, table 1).

In 42% of the households where the mother was an active smoker throughout pregnancy, at

least one parent smoked at home at child age 4 years. In the final model of the pooled analysis,

adjusted for maternal BMI, subcohort and gender following the variable selection procedure,

maternal tobacco smoke exposure status during pregnancy was significantly associated with

child weight status up to 4 years (table 3). Compared to non-smokers, the associations with

child zBMI up to 4 years was as follows: children of passive smokers had on average a higher

zBMI of 0.15 SDs (95% C.I: 0.05, 0.25); for children of partial smokers, zBMI was 0.08 SDs

higher (95% C.I: -0.05, 0.21); and for children of active smokers, zBMI was 0.20 SDs higher

(95% C.I. = 0.08, 0.33). Similar results were observed with child overweight up to four years

(table 3). Only active smoking was significantly associated with rapid weight gain in the first 6

months of life, with an Odds Ratio (OR) of 2.03 (95% C.I: 1.49, 2.76) (table 3). These

associations were similar in the basic models and in additionally-adjusted models that included

further socio-economic and lifestyle indicators as co-variates (table s4). No significant

associations were observed between child postnatal exposure and weight status up to age 4

years: Compared to children who had no parents who smoked, the average zBMI among

children who had one parent that smoked was 0.07 SDs higher (95% C.I: -0.04, 0.18) and for

children that had two parents that smoked it was 0.05 SDs higher (95% C.I: -0.08, 0.19). When

both the prenatal and postnatal exposure variables were included in the same model, the

postnatal estimates were attenuated (table 3).

There was very little difference in estimates when children born prematurely (table s5) or at low

birth weight (table s6) were excluded from the analysis, with the exception of the association

between rapid growth and active maternal smoking during pregnancy which was attenuated

somewhat when low birth weight children were excluded. Repeat of the pooled analysis of

prenatal exposure and child zBMI up to 4 years stratified by key covariates did not provide any

evidence for interaction in effect with gender (p for interaction = 0.65) or social class (p for

interaction = 0.61), although there were slightly stronger effects among boys and larger effects

8

associated with maternal active smoking among children of mothers of lower social class (figure

2). There was a significant interaction with maternal BMI (p for interaction = 0.01), with

stronger effects of maternal passive and active smoking on child zBMI observed among

overweight (BMI > 25) mothers (figure 2).

Menorca subcohort analysisIn the Menorca subcohort 174 (41%) of mothers were non-smokers, 96 (22%) were passive

smokers, 83 (19%) were partial smokers and 74 (17%) were active smokers during pregnancy.

At 4 years, 210 (49%) children had no parents who smoked at home, 146 (34%) had one parent

who smoked and 71 (17%) had two parents who smoked at home. In 78% of the households

where the mother was an active smoker throughout pregnancy, at least parent smoked at home

when the child was aged four years. (table 2). The mean zBMI of children at 4 years in the

Menorca subcohort was 0.59 (SD: 1.01), with 15.2% being classified as overweight. At 14

years, the mean zBMI was 0.34 (SD: 1.04), with 15.3 % being classified as overweight.

In the Menorca analysis, the associations between tobacco smoke exposure and child weight

status were stronger (table 4). Compared to non-smokers, the association between prenatal

exposure groups and child zBMI up to 14 years in the fully adjusted model was as follows:

zBMI was 0.17 SDs higher (95% C.I: -0.06, 0.40) among children of passive smokers, 0.34

SDs higher (95% C.I: 0.10, 0.59) among children of partial smokers, and 0.33 SDs higher (95%

C.I. = 0.08, 0.58) among children of active smokers. In contrast to the pooled analysis there

were significant associations with postnatal tobacco smoke exposure of the child. zBMI up to 14

years among children who had one parent that smoked at the 4 year follow-up was 0.27 SDs

higher (95% C.I: (0.08, 0.47) and for children that had two parents that smoked, it was 0.39 SDs

higher (95% C.I: 0.14, 0.65) compared to children that had no parents who smoked. When the

prenatal and postnatal exposure points were included in the same model, effects at each time

point were attenuated (table 4).

DiscussionOur results have indicated that both passive and active (maternal) exposure to tobacco smoke

are associated with child BMI and overweight. We observed effects of maternal active smoking

that were broadly in line with the effect sizes estimated for the meta analyses by Oken et al. (4)

of 14 studies with overweight at 3–33 years of age (OR = 1.50; 95% CI: 1.36, 1.65) and by Ino

et al (5) for obesity (BMI > 95th percentile, OR = 1.64, 95% CI: 1.42, 1.90) based on 16

studies. The present study adds to the consistency of associations observed across a variety of

social, geographic and temporal contexts. Far less information is available on the effect of

exposure to passive smoke by the mother during pregnancy. Oken et al (7) reported no

association with self-reported levels. Braun et al. (8) used multiple serum cotinine

9

measurements during pregnancy to assess passive smoke exposure and observed a slightly

higher BMI at three years of age in offspring of exposed mothers. Florath (9) used cord serum

cotinine levels to validate maternal non-, passive and active smoker categories during pregnancy

and observed a trend for increased BMI at 8 years in children of passive smokers (of similar

effect size to the present study) and a greater significant effect among children of active

smokers.

Parental smoking during pregnancy may also reflect child passive smoke exposure postnatally.

We did not observe any significant association with zBMI or overweight up to 4 years with

parental smoking during childhood in our larger pooled analysis. However we saw larger

significant associations both prenatally and postnatally with parental smoking in the Menorca

analysis that analyzed effects on child BMI up to 14 years of age. This difference may partially

reflect the greater proportion of mothers who actively smoked during pregnancy that continued

during the early life of their child in Menorca. Furthermore associations with postnatal passive

smoke exposure may only become apparent at later ages. Many studies have reported stronger

effects of tobacco smoke exposure as children become older (8, 10, 13, 26)(11, 27). Changing

attitudes, following the introduction of anti-smoking legislation, in the newer cohorts may also

have resulted in lower exposure levels of the child within each exposure category. A number of

studies have now also associated parental reported measures of postnatal passive smoke

exposure with child BMI (9, 14, 15, 16) however in the presence of multicolinearity between

the pre- and postnatal exposure periods it is difficult to separate the effects of each period.

Moller et al. (12) took advantage of the large sample size in the Danish birth cohort study to

stratify children by exposure prenatally only, postnatally only or exposed at both periods, with

results indicating that exposure at both periods of child development are important.

Although smoking is well known to be related to socio-demographic factors, in the present

study adjustment for lifestyle indicators did not appreciably alter associations with tobacco

smoke exposure and child BMI, strengthening the inference of causality. The weight of

epidemiological evidence is currently stronger for the effects of maternal active smoking than

for passive smoking. We observed strong effects of prenatal passive smoking in both presented

analyses, which may be considered larger than expected relative to the effects of active

smoking, considering the large relative difference in the magnitude of exposure (as indicated by

the urinary cotinine measurements in each exposure group). While the actual effect size of

prenatal passive smoking may in fact be smaller than estimated here within the presented 95%

confidence interval, we may also not expect a linear dose-response curve since passive low dose

exposure may act through a different mechanism than high dose active exposure. We found that

active smoking, but not passive smoking, was associated with rapid growth in the first six

months of life. Early rapid growth is a risk factor for the later development of childhood obesity

10

(28) and can result from impaired fetal growth. We have previously reported within the INMA

study that fetal growth is impaired among actively smoking mothers, which is postulated to

result from placental insufficiency due to vascular damage (29). Alternative mechanisms by

which tobacco smoke exposure may act, even at low dose passive exposure, is through

activation of hormonal systems which influence metabolic programming (30, 31, 32) and/or

through influence of child appetite and circulating leptin levels (33, 34). These results may be

relevant for other environmental pollutants, for which exposure assessment is less certain, that

interact with similar cellular receptors (6).

Since a single urinary cotinine measurement reflects recent tobacco smoke exposure (35), we

primarily used the questionnaire information to classify individuals based on long-term

exposure. While some participants that reported being unexposed had low levels of detectable

cotinine, average cotinine levels in both the mother during pregnancy and in the child were

supportive of the questionnaire-based classification. However, cotinine measurements were not

available in the Menorca subcohort and this information would have allowed us to ascertain if

average exposure levels with passive smoke exposure groupings were different in the older

subcohort. Other limitations include the use of BMI as the outcome measure, which is a blunter

assessment of adiposity than direct measures such as dual-energy X-ray absorptiometry  (36).

Furthermore, a larger sample size may have allowed increased stratification to tease apart the

effects of different exposure periods. However, strengths of this study include its prospective

nature and the use of repeated in-depth face to face interviews with mothers allowing the

collection of detailed information on exposure and lifestyle factors. We employed repeated

measures of BMI over early life and in the older Menorca subcohort, tracked BMI up to 14 year

of age, the oldest yet followed in prospective studies of passive smoke exposure and BMI.

In summary, we have demonstrated an association between both active maternal and passive

tobacco smoke exposure and child BMI and overweight. Although residual confounding cannot

be ruled out, this study adds to a growing body of epidemiological and toxicological evidence

suggesting passive smoke exposure may contribute to the pathogenesis of obesogenic child

growth.

11

Figures and tables

Figure 1. Cotinine measurements (ng/mL,) at 32 weeks of pregnancy and in the child at 4 years. Circles indicate median levels while error bars show 25th and 75th percentiles.

Figure 2. Effect of maternal prenatal tobacco smoke exposure and child zBMI up to 4 years in the 'new' sub cohorts, stratified by key covariates. Maternal social class: CS I-II-III = professional, managerial or skilled occupations; CS IV-V = unskilled occupations.

12

Table 1 . Participant demographic and lifestyle information in the new sub cohorts, by maternal smoking status during pregnancy

Maternal smoking status during pregnancy

Non Smoker697 (36.2)1

Passive Smoker

571 (29.6)

Partial Smoker317 (16.5)

Active smoker342 (17.7) p value

Maternal/Paternal socio-demographics

Maternal education

Primary 110 (26.4)1 95 (22.8) 82 (19.7) 129 (31) <0,001

Secondary 273 (34) 219 (27.3) 145 (18.1) 166 (20.7)

University 312 (44.3) 257 (36.5) 90 (12.8) 46 (6.5)

missing 2 ( 0.1 ) 0 ( 0 ) 0 ( 0 ) 1 ( 0.1 )Maternal Social Class

CSV I+II+III (professional, managerial, skilled) 398 (41.5) 307 (32.1) 140 (14.6) 113 (11.8) <0,001

CS IV+V (unskilled) 298 (30.8) 264 (27.3) 177 (18.3) 229 (23.7)

missing 1 ( 0.1 ) 0 ( 0 ) 0 ( 0 ) 0 ( 0 )Maternal ethnicity

Spain 633 (35.5) 524 (29.4) 296 (16.6) 332 (18.6) 0,016

Other 62 (44.9) 45 (32.6) 21 (15.2) 10 (7.2)missing 2 ( 0.1 ) 2 ( 0.1 ) 0 ( 0 ) 0 ( 0 )

Maternal age

<25 26 (23.4) 27 (24.3) 30 (27) 28 (25.2) <0,001

25-29 184 (30.5) 184 (30.5) 111 (18.4) 125 (20.7)

30-34 318 (37.5) 260 (30.7) 135 (15.9) 134 (15.8)

35+ 168 (46.2) 100 (27.5) 41 (11.3) 55 (15.1)

missing 1 ( 0.1 ) 0 ( 0 ) 0 ( 0 ) 0 ( 0 )Maternal BMI

<18.5 25 (30.5) 17 (20.7) 17 (20.7) 23 (28) 0,027

18.5-25 498 (37.2) 396 (29.6) 226 (16.9) 217 (16.2)

25-30 124 (34.2) 107 (29.5) 60 (16.5) 72 (19.8)

More than 30 50 (34.5) 51 (35.2) 14 (9.7) 30 (20.7)

missing 0 0 0 0Paternal BMI 26.1 ±3.39 25.82 ±3.47 25.82 ±3.18 26.28 ±3.95 0,239

missing 12 (1.7) 14 (2.5) 4 (1.3) 3 (0.9)Maternal urinary cotinine at 32 weeks pregnancy (ng/mL) 8.9 ±59.5 42.8 ±370.9 210.1 ±554.1 2089.5 ±1497.9 <0,001

missing 40 39 33 28

Diet and physical activity of mother during pregnancy

Total Calories (kcals) 1956.69 ±372.4 2029.17 ±471.64 2129.57 ±479.34 2266.67

±518.35 <0,001

missing 10 (1.4) 10 (1.8) 5 (1.6) 6 (1.8)Adjusted total fat (g) 83.45 ±11.17 83.31 ± 11 85.08 ±11.03 85.67 ±10.9) 0,004

missing 10 (1.4) 10 (1.8) 5 (1.6) 6 (1.8)Adjusted proteins (g) 96.16 ±11.67 95.03 ±11.56 94.47 ±11.73 94.33 ±11.75 0,022

missing 10 (1.4) 10 (1.8) 5 (1.6) 6 (1.8)

Adjusted carbohydrates (g) 236.04 ±27.15 237.09 ±28.11 232.85 ±28.38 230.32 ±26.53 0,001

missing 10 (1.4) 10 (1.8) 5 (1.6) 6 (1.8)Adjusted Vegetables (g) 225.64 ±89.64 212.08 205.87 ±96.85 209.05 ±117.43 <0,001

13

Maternal smoking status during pregnancy

Non Smoker697 (36.2)1

Passive Smoker

571 (29.6)

Partial Smoker317 (16.5)

Active smoker342 (17.7) p value

±91.95missing 10 (1.4) 10 (1.8) 5 (1.6) 6 (1.8)

Adjusted Fruits (g) 354.47 ±164.43 337.2 ±160.41 310.45 ±160.27 266.63 ±152.43 <0,001

missing 10 (1.4) 10 (1.8) 5 (1.6) 6 (1.8)Alcohol consumption (g) 0.17 ±0.57 0.25 ±0.88 0.33 ±1.03 0.61 ±1.59 <0,001

missing 10 (1.4) 10 (1.8) 5 (1.6) 6 (1.8)Physical activity per day

during pregnancy (METs) 37.35 ±2.95 37.29 ±3.07 37.06 ±3.21 37.44 ±3.1 0,382

missing 14 (2) 13 (2.3) 7 (2.2) 11 (3.2)

Early life factors Mean length of breast

feeding (months) 27.09 ±22.87 26.29 ±22.03 24.88 ±20.87 20.14 ±22.27 <0,001

missing 12 (1.7) 8 (1.4) 6 (1.9) 4 (1.2)

Birthweight (g) 3306.11 ±446.85 3305.76 ±440.2 3285.02 ±468.39 3124.62

±458.03 <0,001

missing 4 (0.6) 1 (0.2) 2 (0.6) 2 (0.6)Diet and physical activity of child at four years

Total Calories (kcals) 1557.57 ±314.84 1575.44 ±362.97 1610.16 ±384.15 1675.18

±348.26 <0,001

missing 115 (16.5) 91 (15.9) 57 (18) 59 (17.3)Total fat (g) 62.46 ±15.66 62.52 ±17.12 64.39 ±17.46 68.25 ±16.96 <0,001

missing 115 (16.5) 91 (15.9) 57 (18) 59 (17.3)Adjusted3 Vegetables (g) 67.58 ±36.63 67.31 ±39.22 60.79 ±37.89 60.34 ±38.16 0,003

missing 115 (16.5) 91 (15.9) 57 (18) 59 (17.3)

Adjusted Fruits (g) 172.28 ±102.32 157.51 ±102.81 147.59 ±83.51 145.89 ±107.18 <0,001

missing 115 (16.5) 91 (15.9) 57 (18) 59 (17.3)Adjusted proteins (g) 67.79 ±6.96 68.21 ±6.76 68.33 ±7.65 67.48 ±6.79 0,382

missing 115 (16.5) 91 (15.9) 57 (18) 59 (17.3)Adjusted carbohydrates (g) 188.41 ±19.7 188.9 ±19.57 187.35 ±20.54 186.25 ±19.03 0,389

missing 115 (16.5) 91 (15.9) 57 (18) 59 (17.3)Sugar (g) 92.38 ±27.27 94.67 ±33.2 96.36 ±34.61 100.62 ±31.91 0,005

missing 115 (6) 91 (4.7) 57 (3) 59 (3.1)Sleep duration (hours/week) 73.37 ±6.27 72.98 ±6.85 71.93 ±7.88 72.47 ±7.37 0,005

missing 90 (12.9) 73 (12.8) 49 (15.5) 53 (15.5)Tv viewing (hours/week) 9.24 ±5.43 9.85 ±5.84 10.52 ±5.76 10.81 ±6.49 0,001

missing 93 (13.3) 73 (12.8) 50 (15.8) 58 (17)Physical activity per day at

school (METs) 24.98 ±12.04 29.46 ±14.31 30.07 ±15.25 28.87 ±14.12 <0,001

missing 253 (36.3) 222 (38.9) 121 (38.2) 118 (34.5)Child BMI and age at clinical examination

Age at 4 years 4.41 ±0.19 4.42 ±0.22 4.41 ±0.19 4.38 ±0.18 0.027

missing 88 (12.6) 67 (11.7) 50 (15.8) 53 (15.5)

BMI at 1 year 17.23 ±1.32 17.39 ±1.49 17.23 ±1.46 17.49 ±1.52 0.177

missing 216 (31) 195 (34.2) 122 (38.5) 123 (36)

zBMI at 1 year 0.41 ±0.9 0.51 ±0.98 0.43 ±0.96 0.59 ±1 0.156

missing 218 (31.3) 196 (34.3) 123 (38.8) 125 (36.5)

BMI at 4 years 16.11 ±1.49 16.35 ±1.64 16.25 ±1.66 16.4 ±1.77 0.126

14

Maternal smoking status during pregnancy

Non Smoker697 (36.2)1

Passive Smoker

571 (29.6)

Partial Smoker317 (16.5)

Active smoker342 (17.7) p value

missing 90 (12.9) 70 (12.3) 50 (15.8) 53 (15.5)

zBMI at 4 years 0.54 ±0.98 0.68 ±1 0.62 ±1.08 0.70 ±1.07 0.174

missing 90 (12.9) 71 (12.4) 50 (15.8) 54 (15.8)Postnatal Parental smoking status

At child age 1 year

No parent smokes at home 646 (42.4) 479 (31.4) 222 (14.6) 177 (11.6) <0,001

One parent smokes at home 15 (9) 54 (32.3) 40 (24) 58 (34.7)

Both parents smoke at home 2 (1.9) 8 (7.7) 23 (22.1) 71 (68.3)

missing 34 ( 1.9 ) 30 ( 1.7 ) 32 ( 1.8 ) 36 ( 2 )At child age 4 year

No parent smokes at home 579 (44.9) 427 (33.1) 173 (13.4) 110 (8.5) <0,001

One parent smokes at home 20 (9.6) 54 (25.8) 49 (23.4) 86 (41.1)

Both parents smoke at home 2 (1.4) 10 (7.1) 43 (30.7) 85 (60.7)

missing 96 ( 5.9 ) 80 ( 4.9 ) 52 ( 3.2 ) 61 ( 3.7 )

1 n (%) for categorical variables.

2 Mean ± SD for continuous variables.

3 These dietary variables adjusted for total calories consumed

15

Table 2 . Participant demographic and lifestyle information in the Menorca sub cohort, by maternal smoking status during pregnancy

Maternal smoking status during pregnancy

Non Smoker174 (41) 1

Passive Smoker96 (22)

Partial smoker83 (19)

Active smoker74 (17)

p value

Maternal/Paternal socio-demographics

Maternal education

Primary 95 (39.4)1 44 (18.3) 56 (23.2) 46 (19.1) 0.141

Secondary 45 (40.9) 31 (28.2) 16 (14.5) 18 (16.4)

University 26 (46.4) 15 (26.8) 8 (14.3) 7 (12.5)

missing 8 6 3 3

Maternal Social Class

CS I+II+III (professional, managerial, skilled)

118 (44.0) 65 (24.3) 47 (17.5) 38 (14.2) 0.024

CS IV+V (manual or non-manual) 17 (27.4) 14 (22.6) 14 (22.6) 17 (27.4)

missing 39 17 22 19

Maternal age

<25 10 (19.6) 8 (15.7) 19 (37.3) 14 (27.5) 0.010

25-29 74 (42.3) 41 (23.4) 32 (18.3) 28 (16)

30-34 65 (46.1) 31 (22) 23 (16.3) 22 (15.6)

35+ 21 (37.5) 16 (28.6) 9 (16.1) 10 (17.9)

missing 4 0 0 0

Maternal ethnicity

Spain 169 (40.9) 91 (22) 82 (19.9) 71 (17.2) 0.335

Other 3 (25) 5 (41.7) 1 (8.3) 3 (25)

Missing 2 (100) 0 (0) 0 (0) 0 (0)

Maternal BMI

<18.5 6 (30) 3 (15) 6 (30) 5 (25) 0.072

18.5-25 125 (40.6) 71 (23.1) 62 (20.1) 50 (16.2)

25-30 28 (45.9) 8 (13.1) 10 (47.6) 15 (24.6)

More than 30 6 (28.6) 10 (47.6) 3 (14.3) 2 (9.5)

missing 9 4 2 2

Early life factors

Breastfeeding

None 22 (31.4) 16 (22.9) 16 (22.9) 16 (22.9) 0.032

<6 months 70 (35.9) 44 (22.6) 45 (23.1) 36 (18.5)

>= 6 months 82 (50.6) 36 (22.2) 22 (13.6) 22 (13.6)

missing 0 0 0 0

Birth weight (g)2 3249.5 ±490.8 3208.4 ±452.7 3270.9 ±474.06 3035.81 ±403.97 0.003

missing 0 0 0 0

Child physical activity at child age 4 years

Sleep duration (hours / week) 73.27 ±4 72.94 ±4.16 73.24 ±4.85 71.92 ±5.04 0.434

missing 1 0 0 0

TV viewing (hours/week) 7.33 ±3.91 7.66 ±4.19 8.1 ±5.08 8.71 ±4.86 0.282

16

Maternal smoking status during pregnancy

Non Smoker174 (41) 1

Passive Smoker96 (22)

Partial smoker83 (19)

Active smoker74 (17)

p value

missing 1 0 0 1

Outside school physical activity (METs)

14.26 ±12.45 16.32 ±12.8 17.71 ±13.6 15.37 ±13.1 0.057

missing 1 0 0 0

Parental smoking status at child age 4 years

No parent smokes at home 161 (76.7) 26 (12.4) 15 (7.1) 8 (3.8) 0.000

One parent smokes at home 13 (8.9) 64 (43.8) 34 (23.3) 35 (24)

Both parents smoke at home 0 (0) 6 (8.5) 34 (47.9) 31 (43.7)

missing 0 0 0 0

Child characteristics at 14 year clinical examination

Age 14.6 ±0.2 14.6 ±0.2 14.6 ±0.2 14.6 ±0.2 0.268

missing 42 24 25 24

Bmi 20.5 ±2.7 21.2 ±3.6 22.1 ±3.9 22.1 ±3.8 0.002

missing 42 24 25 24

zbmi 0.15 ±0.9 0.32 ±1.1 0.59 ±1.2 0.63 ±1.1 0.009

missing 42 24 25 24

17

Table 3: Adjusted models in the pooled analysis of the four 'new' INMA cohorts, showing relationships between tobacco smoke exposure and child weight status measured at 1 and 4 years of age and rapid growth in the first six months of life.

zBMI1 Overweight1 Rapid growth 0-6 month2

N Beta (95% CI) N of cases/controls OR (95% CI)

N of case/

controlsOR (95% CI)

Smoking status of mother during pregnancy

Non smoker 683 0 118/565 1 133/472 1

Passive smoker 553 0.15 (0.05, 0.25) 119/434 1.36 (1.02, 1.80) 110/393 0.99 (0.75, 1.33)

Partial smoker 303 0.08 (-0.05, 0.21) 58/245 1.30 (0.91, 1.84) 77/197 1.34 (0.97, 1.87)

Active smoker 327 0.20 (0.08, 0.33) 83/244 1.78 (1.29, 2.45) 115/190 2.03 (1.49, 2.76)

Postnatal tobacco exposure of the child

No parent smokes 1527 0 282/1245 1

1 parent smokes 204 0.07 (-0.04, 0.18) 62/142 1.14 (0.82, 1.57)Both parents

smoke 135 0.05 (-0.08, 0.19) 34/101 0.99 (0.65, 1.5)

Prenatal and postnatal exposure (mutually adjusted model)

Smoking status of mother during pregnancy

Non smoker 683 0 118/565 1

Passive smoker 553 0.16 (0.06, 0.27) 119/434 1.36 (1.02, 1.81)

Partial smoker 303 0.09 (-0.04, 0.22) 58/245 1.31 (0.92, 1.88)

Active smoker 327 0.20 (0.06, 0.33) 83/244 1.90 (1.33, 2.69)

Postnatal tobacco exposure of the child

No parent smokes 1527 0 282/1245 1

1 parent smokes 204 0.02 (-0.10, 0.14) 62/142 0.93 (0.66, 1.3)Both parents

smoke 135 0.03 (-0.13, 0.18) 34/101 0.74 (0.48, 1.16)

1. Adjusted by subcohort, sex and maternal pre-pregnancy BMI

2. Adjusted by subcohort and gender

18

Table 4. Adjusted models in the Menorca subcohort analysis showing relationships between tobacco smoke exposure and child weight status measured at 4, 6, 11 and 14 years of age

zBMI1 Overweight1

N Beta (95% CI)N of

cases/controls

OR (95% CI)

Smoking status of mother during pregnancyNon smoker 174 0 32/142 1

Passive smoker 96 0.17 (-0.06, 0.40) 25/71 2.09 (1.13, 3.87)

Partial smoker 83 0.34 (0.10, 0.59) 23/60 3.12 (1.71, 5.69)

Active smoker 74 0.33 (0.08, 0.58) 25/49 2.90 (1.58, 5.32)

Postnatal tobacco exposure of the child at 4 years

No parent smokes 210 0 38/172 1

1 parent smokes 146 0.27 (0.08, 0.47) 42/104 2.38 (1.44, 3.94)

Both parents smoke 71 0.39 (0.14, 0.65) 27/44 3.40 (1.92, 6.02)

Prenatal and postnatal exposure (mutually adjusted model)

Smoking status of mother during pregnancy

Non smoker 174 0 32/142 1

Passive smoker 96 0.03 (-0.26, 0.32) 25/71 1.40 (0.65, 3.00)

Partial smoker 83 0.16 (-0.16, 0.48) 23/60 1.82 (0.81, 4.06)

Active smoker 74 0.13 (-0.20, 0.47) 25/49 1.63 (0.71, 3.74)

Tobacco exposure post pregnancy 4 year

No parent smokes 210 0 38/172 1

1 parent smokes 146 0.21 (-0.05, 0.48) 42/104 1.77 (0.90, 3.47)

Both parents smoke 71 0.27 (-0.07, 0.61) 27/44 2.24 (1.00, 4.98)

1 Adjusted by sex and maternal pre-pregnancy BMI

19

References

1. Ng M, Fleming T, Robinson M, Thomson B, Graetz N, Margono C, et al. Global, regional, and national prevalence of overweight and obesity in children and adults during 1980 - 2013: a systematic analysis for the Global Burden of Disease Study 2013. The Lancet 2014;384: 766-781.

2. McAllister EJ, Dhurandhar NV, Keith SW, Aronne LJ, Barger J, Baskin M, et al. Ten Putative Contributors to the Obesity Epidemic. Critical Reviews in Food Science and Nutrition 2009;49: 868-913.

3. Thayer KA, Heindel JJ, Bucher JR, Gallo MA. Role of environmental chemicals in diabetes and obesity: a National Toxicology Program workshop review. Environ Health Perspect 2012;120: 779-789.

4. Oken E, Levitan EB, Gillman MW. Maternal smoking during pregnancy and child overweight: systematic review and meta-analysis. Int J Obes 2007;32: 201-210.

5. Ino T. Maternal smoking during pregnancy and offspring obesity: meta-analysis. Pediatr Int 2010;52: 94-99.

6. Behl M, Rao D, Aagaard K, Davidson TL, Levin ED, Slotkin TA, et al. Evaluation of the association between maternal smoking, childhood obesity, and metabolic disorders: a national toxicology program workshop review. Environ Health Perspect 2013;121: 170-180.

7. Oken E, Huh SY, Taveras EM, Rich-Edwards JW, Gillman MW. Associations of maternal prenatal smoking with child adiposity and blood pressure. Obes Res 2005;13: 2021-2028.

8. Braun JM, Daniels JL, Poole C, Olshan AF, Hornung R, Bernert JT, et al. Prenatal environmental tobacco smoke exposure and early childhood body mass index. Paediatr Perinat Epidemiol 2010;24: 524-534.

9. Florath I, Kohler M, Weck MN, Brandt S, Rothenbacher D, Schottker B, et al. Association of pre- and post-natal parental smoking with offspring body mass index: an 8-year follow-up of a birth cohort. Pediatr Obes 2013;9: 121-134.

10. Howe LD, Matijasevich A, Tilling K, Brion MJ, Leary SD, Smith GD, et al. Maternal smoking during pregnancy and offspring trajectories of height and adiposity: comparing maternal and paternal associations. Int J Epidemiol 2012;41: 722-732.

11. Durmus B, Heppe DH, Taal HR, Manniesing R, Raat H, Hofman A, et al. Parental smoking during pregnancy and total and abdominal fat distribution in school-age children: the Generation R Study. Int J Obes (Lond) 2014;38: 966-972.

20

12. Moller SE, Ajslev TA, Andersen CS, Dalgard C, Sorensen TI. Risk of childhood overweight after exposure to tobacco smoking in prenatal and early postnatal life. PLoS One 2014;9: e109184.

13. Harris HR, Willett WC, Michels KB. Parental smoking during pregnancy and risk of overweight and obesity in the daughter. Int J Obes (Lond) 2013;37: 1356-1363.

14. Griffiths LJ, Hawkins SS, Cole TJ, Dezateux C. Risk factors for rapid weight gain in preschool children: findings from a UK-wide prospective study. Int J Obes (Lond) 2010;34: 624-632.

15. Raum E, Kupper-Nybelen J, Lamerz A, Hebebrand J, Herpertz-Dahlmann B, Brenner H. Tobacco smoke exposure before, during, and after pregnancy and risk of overweight at age 6. Obesity (Silver Spring) 2011;19: 2411-2417.

16. McConnell R, Shen E, Gilliland FD, Jerrett M, Wolch J, Chang CC, et al. A longitudinal cohort study of body mass index and childhood exposure to secondhand tobacco smoke and air pollution: the Southern California Children's Health Study. Environ Health Perspect 2014;123: 360-366.

17. Guxens M, Ballester F, Espada M, Fernandez MF, Grimalt JO, Ibarluzea J, et al. Cohort Profile: the INMA--INfancia y Medio Ambiente--(Environment and Childhood) Project. Int J Epidemiol 2012;41: 930-940.

18. Liberatos P, Link BG, Kelsey JL. The measurement of social class in epidemiology. Epidemiol Rev 1988;10: 87-121.

19. Ridley K, Ainsworth BE, Olds TS. Development of a compendium of energy expenditures for youth. Int J Behav Nutr Phys Act 2008;5: 45.

20. Willett W, Stampfer MJ. Total energy intake: implications for epidemiologic analyses. Am J Epidemiol 1986;124: 17-27.

21. Aurrekoetxea JJ, Murcia M, Rebagliato M, Lopez MJ, Castilla AM, Santa-Marina L, et al. Determinants of self-reported smoking and misclassification during pregnancy, and analysis of optimal cut-off points for urinary cotinine: a cross-sectional study. BMJ Open 2013;3.

22. Aurrekoetxea JJ, Murcia M, Rebagliato M, Guxens M, Fernández-Somoano A, López MJ, et al. Second-hand smoke exposure in 4-year-old children in Spain: Sources, associated factors and urinary cotinine. Environmental Research 2016;145: 116-125.

23. de Onis M, Garza C, Onyango AW, Rolland-Cachera MF. [WHO growth standards for infants and young children]. Arch Pediatr 2009;16: 47-53.

24. Valvi D, Mendez MA, Garcia-Esteban R, Ballester F, Ibarluzea J, Goni F, et al. Prenatal exposure to persistent organic pollutants and rapid weight gain and overweight in infancy. Obesity (Silver Spring) 2013;22: 488-496.

25. Spratt M, Carpenter J, Sterne JAC, Carlin JB, Heron J, Henderson J, et al. Strategies for Multiple Imputation in Longitudinal Studies. American Journal of Epidemiology 2010;172: 478-487.

21

26. Durmus B, Ay L, Hokken-Koelega AC, Raat H, Hofman A, Steegers EA, et al. Maternal smoking during pregnancy and subcutaneous fat mass in early childhood. The Generation R Study. Eur J Epidemiol 2011;26: 295-304.

27. Riedel C, Fenske N, Muller MJ, Plachta-Danielzik S, Keil T, Grabenhenrich L, et al. Differences in BMI z-scores between offspring of smoking and nonsmoking mothers: a longitudinal study of German children from birth through 14 years of age. Environ Health Perspect 2014;122: 761-767.

28. Ong KK, Ahmed ML, Emmett PM, Preece MA, Dunger DB. Association between postnatal catch-up growth and obesity in childhood: prospective cohort study. Bmj 2000;320: 967-971.

29. Íñiguez C, Ballester F, Costa O, Murcia M, Souto A, Santa-Marina L, et al. Maternal smoking during pregnancy and fetal biometry: the INMA Mother and Child Cohort Study. Am J Epidemiol 2013;178: 1067-1075.

30. Irigaray P, Ogier V, Jacquenet S, Notet V, Sibille P, Mejean L, et al. Benzo[a]pyrene impairs beta-adrenergic stimulation of adipose tissue lipolysis and causes weight gain in mice. A novel molecular mechanism of toxicity for a common food pollutant. Febs J 2006;273: 1362-1372.

31. Levin ED. Fetal nicotinic overload, blunted sympathetic responsivity, and obesity. Birth Defects Res A Clin Mol Teratol 2005;73: 481-484.

32. Oncken CA, Henry KM, Campbell WA, Kuhn CM, Slotkin TA, Kranzler HR. Effect of maternal smoking on fetal catecholamine concentrations at birth. Pediatr Res 2003;53: 119-124.

33. Pardo IM, Geloneze B, Tambascia MA, Barros-Filho AA. Does maternal smoking influence leptin levels in term, appropriate-for-gestational-age newborns? J Matern Fetal Neonatal Med 2004;15: 408-410.

34. Toschke AM, Ehlin AG, von Kries R, Ekbom A, Montgomery SM. Maternal smoking during pregnancy and appetite control in offspring. J Perinat Med 2003;31: 251-256.

35. Benowitz NL. Biomarkers of environmental tobacco smoke exposure. Environ Health Perspect 1999;107 Suppl 2: 349-355.

36. Freedman DS, Sherry B. The validity of BMI as an indicator of body fatness and risk among children. Pediatrics 2009;124 Suppl 1: S23-34.

22