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Parental smoking behaviour and effects of tobacco smoke on children's health in Finland and Russia

Timo T. Hugg, Maritta S. Jaakkola, Risto O. Ruotsalainen, Vadim J. Pushkarev, Jouni J.K. Jaakkola
DOI: http://dx.doi.org/10.1093/eurpub/ckm053 55-62 First published online: 14 June 2007

Abstract

Background: There is little information on potential differences in smoking behaviour of parents between Finland and Russia and on the effects of environmental tobacco smoke (ETS) exposure on allergic and respiratory diseases among Finnish and Russian children. The aim of the study was to compare the smoking behaviour of parents and school children and to assess the relations of tobacco smoke exposure during pregnancy and childhood with occurrence of allergic diseases and respiratory infections among school children. Methods: We conducted a population-based cross-sectional study in the neighbour towns across the border of Imatra in Finland and Svetogorsk in Russia. The study population consisted of 512 Finnish and 581 Russian school children aged 7–16 years (response rate 79%). Results: Children's tobacco smoke exposure differed markedly between Finland and Russia. The risk of asthma was particularly related to high maternal smoking exposure during pregnancy (adjusted OR 3.51, 95% CI 1.00–12.3), infancy (3.34, 1.23–9.07) and currently (3.27, 1.26–8.48), and the risk of common cold was related to high combined parental smoking during infancy (1.83, 1.06–3.17) in Finnish children. Among Russian children allergic conjunctivitis was related to maternal smoking during infancy (4.53, 1.49–13.8) and currently (2.82, 1.07–7.44). Conclusions: Smoking behaviour of parents and ETS exposure during childhood differed markedly between Finland and Russia. Asthma was particularly increased in relation to high exposure to maternal smoking in Finland. The results suggest that more efforts should be directed to reducing tobacco smoke exposure of children in both Finland and Russia. (250 words)

  • allergies
  • asthma
  • children
  • respiratory infections
  • smoking behaviour
  • tobacco smoke exposure

Introduction

Environmental tobacco smoke (ETS) is a common indoor exposure worldwide. Inspite of anti-tobacco campaigns and stricter tobacco control laws in some countries, ETS still remains a major health hazard in many private and public facilities in many European countries and elsewhere. Since the 1970s smoking has decreased in most western countries among men, whereas the prevalence of smoking has increased among women in both Eastern and Western Europe and men in Eastern Europe.1 In 1990s, as much as 25% of the Nordic children were exposed weekly to ETS at home.2

Both pre- and post-natal passive smoking have been linked to the occurrence of asthma and increased frequency of other respiratory illnesses and symptoms in childhood.3–6 However, evidence of the effects of ETS exposure on allergies is inconsistent.3,,6–9

There are a number of studies on asthma and respiratory symptoms in relation to environmental tobacco smoke in children,3,,10 but only a few have examined national differences in smoking behaviour of parents.2,,11 The aim of the study was to compare the smoking behaviour of parents and school children between Finland and Russia and to assess the effects of pre-natal, post-natal and current exposure to tobacco smoke on the risk of allergic diseases and respiratory infections among schoolchildren living on either side of the shared border in the towns of Imatra, Finland and Svetogorsk, Russia.

Methods

Study population

A cross-sectional population-based study was conducted in the towns of Imatra, Finland and Svetogorsk, Russia, from October to November 2003. Imatra, with 30 000 inhabitants, is located in the south-eastern part of Finland, and Svetogorsk, with 17 000 inhabitants is located in the westernmost part of Saint Petersburg region. Both study areas are located at the border district of the two countries (figure 1). As part of a municipal cooperation project called ‘Twin City’, the study was approved by the local ethics authorities of school and health affairs in both towns.

Figure 1

Map of the study area

The source population consisted of all school children in the two municipalities. Participating primary schools, altogether four in Imatra and two in Svetogorsk, were selected so that they were located in the middle of the districts, representing the area and populations of interest. School children 7–16 years of age were invited to participate and those who returned a completed questionnaire formed the study population.

Questionnaire

A self-administered questionnaire modified from the International Study of Asthma and Allergies in Childhood (ISAAC, Phase Two and Three) and two previous Finnish questionnaires were distributed by school teachers to 1400 school children between 7 and 16 years of age.12–15 These questionnaires have been tested and validated.12–15 Teachers, parents and school children were given oral and written instructions about distributing and filling in the questionnaires. The questionnaires were filled in anonymously at home by the school children together with their parents and returned by the child to his/her teacher.

Health outcomes

The health outcomes were based on questionnaire information. They included asthma, allergic rhinitis, allergic conjunctivitis and the number of respiratory infections during the past twelve months. The questions concerning allergy were as follows: ‘Does your child have any allergy?’ (no/yes), ‘If yes, does your child have asthma and/or allergic rhinitis and/or allergic conjunctivitis?’ The question concerning respiratory infections was as follows: ‘How many times did the child suffer from tonsillitis, otitis media, sinusitis, bronchitis, pneumonia and/or common cold/flu during the past 12 months?’

Exposure assessment

The exposure assessment was based on questionnaire information on parental smoking habits. The following exposure indices were formed to characterise exposure during pregnancy (pre-natal exposure), during the child's first year of life (early-life exposure) and at the time of the survey (current exposure). Pre-natal exposure was estimated from maternal smoking during pregnancy (yes/no). The exposure was categorized into high (more than 10 cigarettes/day), low (up to 10 cigarettes/day) and no exposure (no smoking) on the basis of current smoking rate. Early-life exposure was estimated in two ways: (i) from maternal smoking during the child's first year of life (yes/no) and smoking rate (no smoking; low: up to 10 cigarettes/day; high: more than 10 cigarettes/day); and (ii) a combination of maternal smoking during the child's first year of life (yes/no) and paternal smoking taking into account paternal smoking rate (no, low, and high as above). We assessed current exposure at the time of the study from maternal and paternal smoking separately (no, low and high as above) as well as from combined smoking by mother and father (no smoking; low: up to 15 cigarettes/day; high: more than 15 cigarettes/day). In addition, the questionnaire included a question about personal smoking: ‘Does your child smoke cigarettes?’ (yes/no).

Statistical methods

First, we compared smoking habits and behaviour between Finnish and Russian parents and children. χ2- and t-tests were used to assess the statistical significance of differences between these groups. Second, we assessed the relations of pre-, post-natal and current tobacco smoke exposures to health outcomes using odds ratio as a measure of effect. Multiple logistic regression analysis was used to estimate odds ratios (OR and 95% confidence intervals, CI) adjusted for the following core covariates: study area, age, gender, early-life and current pets, any dampness or mould problems and parental allergy. All statistical analyses were performed using the statistical package SAS, version 9.1 (SAS Institute, Cary, NC, USA).

Results

Study population

A total of 1106 (response rate 79.0%) subjects completed the questionnaire, 519 (74.1%) in Imatra and 587 (83.9%) in Svetogorsk. Information on age was missing in 11 subjects and gender in two subjects, who were excluded. Thus, the final study population included a total of 1093 children, 512 from Finland and 581 from Russia. In Finland, 265 (51.8%) respondents were boys and 247 (48.2%) girls. In Russia, the corresponding numbers were 252 (43.4%) and 329 (56.6%), respectively.

Smoking behaviour

The time pattern of exposure to tobacco smoke differed substantially between the Finnish and Russian children. Current regular indoor exposure to tobacco smoke and paternal smoking were significantly more common among school children in Svetogorsk than in Imatra (table 1). Proportion of current maternal smoking did not differ between the countries, but exposure to maternal smoking during pregnancy and during child's first year of life were more frequent in Finland than in Russia. The proportions of heavy smokers (≥15 cigarettes per day) were clearly higher among both smoking parents in Finland than in Russia. Also the average number of cigarettes smoked daily was higher among both parents in Finland compared to Russia (female smokers 11.8 versus 7.9, t-test: P < 0.001; male smokers 15.6 versus 13.5, t-test: P = 0.001). The prevalence of smoking by the children themselves was low. It was more common among Russian than Finnish children.

View this table:
Table 1

Self-reported exposure to tobacco smoke and personal smoking among schoolchildren in Imatra, Finland (Ntot = 512), and in Svetogorsk, Russia (Ntot = 581), 2003

Exposure variableImatra% (n)Svetogorsk% (n)P-valuea
Current regular indoor exposure to tobacco smoke (N = 512/571)1.4 (7)32.9 (188)<0.001
Mother smoking (N = 504/573)27.0 (136)24.8 (142)0.410
Mother smoking ≥ 15 cigarettes/dayb38.0 (46)7.8 (10)<0.001
Mother smoked during pregnancy (N = 501/566)14.0 (70)6.7 (38)<0.001
Mother smoked during child's first year of life (N = 500/566)22.8 (114)8.8 (50)<0.001
Father smoking (N = 495/560)39.6 (196)62.3 (349)<0.001
Father smoking ≥ 15 cigarettes/dayc64.9 (111)47.5 (145)<0.001
Child smoking (N = 506/574)1.2 (6)4.4 (25)<0.01
  • a: χ2 test

  • b: Denominator is the number of smokers with information on smoking rate: Imatra 121, Svetogorsk 129

  • c: Denominator is the number of smokers with information on smoking rate: Imatra 171, Svetogorsk 305

Health effects

The preliminary analyses of ETS exposure and health outcomes showed differences in the effect estimates between Finnish and Russian children, which were at least partly explained by the different exposure patterns, and because of that, the results on the effects of exposure are presented separately for Finnish and Russian children. As a consequence of smaller numbers in these subcategories, the precision of the estimates was compromised for some outcomes.

Among Finnish children, the risk of asthma was particularly related to high maternal smoking during pregnancy (adjusted OR 3.51, 95% CI 1.00–12.3), during the first year of life (3.34, 1.23–9.07), and currently (3.27, 1.26–8.48) (table 2). Exposure-response relations were also observed for combined parental smoking in the first year of life (adjusted OR for low exposure: 1.36, 95% CI 0.57–3.24; high exposure: 2.66, 1.01–7.00), and for current parental exposure (low exposure: 1.60, 0.69–3.71; high exposure: 2.91, 1.05–8.09). The risk of any allergic disease was elevated in relation to high maternal smoking at the time of the study (1.94, 1.03–3.64).

View this table:
Table 2

Tobacco smoke exposure and health outcomes in Finnish children. Adjusted odds ratios (OR) for respiratory health outcomes according to pre-natal, early-life and current exposure to tobacco smoke in Finnish children (n = 512). Low and high exposure groups were compared to no exposure as the reference category

Health outcomeMaternal smoking in pregnancy n = 70Maternal smoking during the child's first year of life n = 114Early-life exposurean = 229Current maternal smoking n = 136Current paternal smoking n = 196Current maternal and/or paternal smokingbn = 238
Lowcn = 40 Adjusted ORe (95%CI)Highdn = 30 Adjusted ORe (95%CI)Lowcn = 67 Adjusted ORe (95% CI)Highdn = 47 Adjusted ORe (95% CI)Lowcn = 156 Adjusted ORe (95% CI)Highdn = 73 Adjusted ORe (95% CI)Lowcn = 80 Adjusted ORe (95% CI)Highdn = 56 Adjusted ORe (95% CI)Lowcn = 76 Adjusted ORe (95% CI)Highdn = 120 Adjusted ORe (95% CI)Lowfn = 175 Adjusted ORe (95% CI)Highgn = 63 Adjusted ORe (95% CI)
Asthma0.89 (0.20–4.05)3.51 (1.00–12.3)1.10 (0.35–3.43)3.34 (1.23–9.07)1.36 (0.57–3.24)2.66 (1.01–7.00)1.04 (0.34–3.24)3.27 (1.26–8.48)1.07 (0.33–3.46)2.15 (0.95–4.89)1.60 (0.69–3.71)2.91 (1.05–8.09)
Rhinitis0.61 (0.21–1.77)0.48 (0.11–2.10)1.06 (0.50–2.21)1.18 (0.49–2.83)1.24 (0.71–2.19)1.12 (0.52–2.40)0.91 (0.44–1.88)1.29 (0.57–2.81)1.18 (0.56–2.46)1.27 (0.70–2.31)1.15 (0.66–2.01)1.33 (0.61–2.89)
Conjunctivitis1.06 (0.13–8.70)0.69 (0.15–3.12)1.92 (0.51–7.28)2.14 (0.84–5.42)0.91 (0.19–4.38)0.95 0.27–3.39)1.61 (0.43–6.01)1.40 (0.42–4.61)1.17 (0.40–3.44)2.29 (0.90–5.82)1.24 (0.25–6.06)
Any allergy0.53 (0.22–1.25)1.67 (0.71–3.90)0.80 (0.43–1.48)1.84 (0.93–3.62)1.14 (0.72–1.81)1.32 (0.73–2.40)0.69 (0.37–1.27)1.94 (1.03–3.64)1.17 (0.64–2.12)1.35 (0.84–2.19)1.13 (0.72–1.78)1.58 (0.85–2.95)
Tonsillitis1.06 (0.24–4.75)0.68 (0.09–5.40)1.94 (0.72–5.20)0.39 (0.05–3.09)1.62 (0.66–3.98)1.45 (0.44–4.81)1.85 (0.69–4.92)0.70 (0.15–3.22)0.87 (0.24–3.22)1.88 (0.76–4.64)1.42 (0.58–3.48)1.68 (0.50–5.60)
Otitis media0.61 (0.21–1.78)1.22 (0.44–3.37)0.99 (0.47–2.05)0.68 (0.26–1.81)0.66 (0.37–1.20)0.78 (0.37–1.64)1.03 (0.52–2.03)0.84 (0.36-1.98)0.56 (0.24–1.30)0.88 (0.49–1.59)0.78 (0.45–1.37)0.85 (0.39–1.86)
Sinusitis2.45 (0.74–8.10)1.70 (0.58–5.01)0.47 (0.06–3.76)0.40 (0.12–1.31)1.08 (0.33–3.52)2.13 (0.78–5.82)0.42 (0.05–3.37)0.45 (0.09–2.15)1.14 (0.41–3.16)0.67 (0.24–1.90)1.56 (0.47–5.22)
Bronchitis1.61 (0.52–4.98)1.50 (0.57–3.91)1.04 (0.29–3.69)1.18 (0.53–2.60)0.93 (030–2.89)1.57 (0.64–3.87)0.85 (0.24–2.99)0.85 (0.30–2.41)1.06 (0.45–2.53)0.89 (0.40–1.98)0.97 (0.31–3.02)
Cold/flu1.28 (0.66–2.48)1.46 (0.67–3.19)1.49 (0.84–2.46)1.25 (0.67–2.33)1.10 (0.73–1.65)1.83 (1.06–3.17)1.51 (0.91–2.50)1.61 (0.89–2.91)1.18 (0.70–1.98)1.49 (0.96–2.30)1.03 (0.70–1.53)1.63 (0.92–2.90)
  • Blank columns indicates that there were not enough exposed cases to assess OR

  • a: Maternal smoking during the child's first year of life and paternal smoking combined

  • b: Current maternal and/or paternal smoking combined

  • c: Up to 10 cigarettes per day

  • d: More than 10 cigarettes per day

  • e: Adjusted for age, gender, early-life and current pets, any dampness or mould problems, parental allergy

  • f: Up to 15 cigarettes per day

  • g: More than 15 cigarettes per day

Of respiratory infections, the risk of common cold/flu was elevated in relation to high combined parental exposure in the child's first year of life (1.83, 1.06–3.17).

In Russia, maternal smoking in pregnancy (6.7%) and during the child's first year of life was rare (8.8%) and consequently, the corresponding effect estimates were imprecise (tables 1 and 3). The effect estimates for asthma showed some similar trends, though not statistically significant, with those of the Finnish children and the risk of asthma was particularly related to current high exposure to maternal smoking (adjusted OR 4.58, 95% CI 0.84–25.0; table 3). The risk of conjunctivitis was particularly related to maternal smoking during the child's first year of life (low exposure: 4.53, 1.49–13.8), and currently (low exposure: 2.82, 1.07–7.44). The risks of respiratory infections did not show obvious significant relations with tobacco smoke, but the risk of most infections was increased in relation to maternal heavy smoking in the child's first year of life, while parental smoking showed an inverse relation with common cold.

View this table:
Table 3

Tobacco smoke exposure and health outcomes in Russian children. Adjusted odds ratios (OR) for respiratory health outcomes according to pre-natal, early-life and current exposure to tobacco smoke in Russian children (N = 581). Low and high exposure groups were compared to no exposure as the reference category

Health outcomeMaternal smoking in pregnancy n = 38Maternal smoking during the child's first year of life n = 50Early-life exposurean = 364Current maternal smoking n = 142Current paternal smoking n = 349Current maternal and paternal smokingbn = 387
Lowcn = 35 Adjusted ORe (95% CI)Highdn = 3 Adjusted ORe (95% CI)Lowcn = 44 Adjusted ORe (95% CI)Highdn = 6 Adjusted ORe (95% CI)Lowcn = 296 Adjusted ORe (95% CI)Highdn = 73 Adjusted ORe (95% CI)Lowcn = 129 Adjusted ORe (95% CI)Highdn = 13 Adjusted ORe (95% CI)Lowcn = 185 Adjusted ORe (95% CI)Highdn = 164 Adjusted ORe (95% CI)Lowfn = 335 Adjusted ORe (95% CI)Highgn = 52 Adjusted ORe (95% CI)
Asthma0.82 (0.10–6.54)0.69 (0.09–5.43)0.64 (0.24–1.72)1.40 (0.40–4.92)0.64 (0.18–2.30)4.58 (0.84–25.0)0.78 (0.27–2.25)0.95 (0.32–2.79)0.72 (0.28–1.90)1.42 (0.35–5.79)
Rhinitis0.75 (0.17–3.37)0.88 (0.25–3.06)0.97 (0.49–1.91)1.06 (0.39–2.92)0.84 (0.37–1.91)2.13 (0.42–10.8)0.79 (0.37–1.67)0.96 (0.45–2.07)0.93 (0.47–1.84)1.18 (0.39–3.53)
Conjunctivitis2.89 (0.77–10.9)4.53 (1.49–13.8)0.63 (0.21–1.93)2.22 (0.66–7.47)2.82 (1.07–7.44)0.71 (0.23–2.17)0.57 (0.17–1.95)0.82 (0.28–2.45)2.70 (0.70–10.4)
Any allergy0.72 (0.28–1.84)1.16 (0.55–2.47)0.88 (0.57–1.35)0.86 (0.44–1.70)1.12 (0.68–1.83)1.35 (0.37–4.90)0.69 (0.43–1.11)0.84 (0.51–1.38)0.99 (0.64–1.53)0.72 (0.32–1.61)
Tonsillitis1.04 (0.48–2.27)1.23 (0.57–2.26)3.47 (0.57–21.2)0.86 (0.58–1.28)1.21 (0.67–2.19)1.08 (0.69–1.68)1.56 (0.48–5.01)0.68 (0.43–1.06)1.12 (0.72–1.74)0.78 (0.52–1.15)1.21 (0.62–2.38)
Otitis media0.55 (0.07–4.31)0.43 (0.06–3.35)3.57 (0.35–36.1)1.20 (0.53–2.71)0.70 (0.15–3.36)0.82 (0.30–2.26)1.68 (0.20–14.2)1.22 (0.51–2.89)0.81 (0.29–2.27)1.05 (0.47–2.38)0.44 (0.05–3.63)
Sinusitis0.55 (0.12–2.39)0.41 (0.10–1.74)1.79 (0.19–16.6)1.25 (0.69–2.26)1.41 (0.58–3.41)0.72 (0.35–1.48)0.66 (0.08–5.20)1.15 (0.60–2.23)1.48 (0.77–2.87)1.27 (0.70–2.33)1.52 (0.56–4.12)
Bronchitis0.82 (0.28–2.44)0.98 (0.40–2.44)1.99 (0.16–13.74)1.18 (0.70–2.00)1.40 (0.64–3.04)1.38 (0.79–2.41)1.25 (0.27–5.88)1.26 (0.71–2.23)1.32 (0.73–2.39)1.30 (0.76–2.24)1.80 (0.76–4.25)
Cold/flu0.60 (0.22–1.63)0.52 (0.21–1.26)0.85 (0.09–7.86)0.71 (0.46–1.09)0.51 (0.26–1.06)0.67 (0.40–1.13)0.25 (0.03–1.97)0.60 (0.37–0.98)0.76 (0.47–1.24)0.78 (0.51–1.20)0.31 (0.11–0.83)
  • Blank columns indicate that there were not enough exposed cases to assess OR

  • a: Maternal smoking during the child's first year of life and paternal smoking combined

  • b: Current maternal and paternal smoking combined

  • c: Up to 10 cigarettes per day

  • d: More than 10 cigarettes per day

  • e: Adjusted for age, gender, early-life and current pets, any dampness or mould problem, parental allergy

  • f: Up to 15 cigarettes per day

  • g: More than 15 cigarettes per day

Discussion

Smoking behaviour of parents differed markedly between Finland and Russia. Current regular indoor exposure to tobacco smoke and paternal smoking were significantly higher in Russia, whereas heavy smoking (≥15 cigarettes/day) was more common among both parents in Finland. Inspite of well-developed national maternity and childcare clinic system in Finland, maternal smoking during pregnancy and child's first year of life was higher in Finland, although current maternal smoking was equally common in both countries. This result challenges the effectiveness of the recent anti-tobacco campaigns in Finland and other western countries where smoking among females is still relatively common, even during pregnancy. The results also suggest that smoking cessation during pregnancy seems to be temporary and smoking returns soon after pregnancy back to higher level, especially in Finnish women.

In Finnish children, the risk of asthma was increased in relation to maternal smoking during pregnancy, during infancy and at the time of the study, with an exposure-response pattern. Among Russian children, early-life and current exposure to maternal tobacco smoke were associated with an increased risk of allergic conjunctivitis. In Finland, the occurrence of common colds/flues was consistently elevated in the high exposure groups, but in Russia common cold/flu showed no increase in relation to tobacco smoke exposure. This difference could be explained at least partly by different diagnostic practices between Finland and Russia.

Validity of results

The ISAAC questionnaire was designed and standardized to allow comparisons of the occurrence of atopic diseases and some of their determinants, such as smoking habits, between and within populations in different countries. However, our results may be affected by some methodological limitations. The translation of the questionnaire into Russian was not standardized, so some disagreements between the two languages, cultural differences in understanding and filling in the questionnaire, and different definitions of diseases used in Finland and Russia are possible sources of bias, although both the professional certified translator and the Russian medical expert had experience from similar type of studies.

Although the response rate was relatively high in both study areas, the possibility of selection bias cannot be totally excluded. We used self-reported allergies instead of doctor- diagnosed allergies because of the likelihood of national differences in diagnostic procedures.16 When comparing results using either self-reported or doctor-diagnosed allergies no substantial differences were observed. The public awareness of allergies and other respiratory problems is relatively high in both Svetogorsk and Imatra due to several air pollution and health studies conducted in the area in the 1980s–90s.12,,13 Therefore appropriate identification and reporting of allergic diseases and respiratory infections could be expected. Potential underreporting of smoking status and smoking levels cannot be ruled out, especially in Russia, where women's smoking has been traditionally relatively uncommon and socially unacceptable.17,,18 Because of low numbers of respondents reporting maternal smoking during pregnancy and early childhood in Russia, results concerning smoking, especially heavy smoking, during these periods should be interpreted with caution. However, previous studies have reported high correlation between self-reported smoking or self-reported exposure to tobacco smoke and objective biochemical measures of exposure.19,,20 In addition, consistency between the results on health effects of this study and those from other studies support the validity of the current study.6,,21 Anonymity while answering the questionnaire was guaranteed to support honest and accurate reporting.

Synthesis with previous knowledge

Exposure to parental smoking

Despite variation in the definitions and criteria used for exposure, the overall occurrence of indoor exposure to tobacco smoke and the prevalence of smoking fathers in both study areas were in line with previous results reported from the countries.6,,11,22–26 The proportion of smoking mothers and maternal smoking during pregnancy was in Svetogorsk among the highest ever reported from Russia, whereas in Finland the smoking prevalences were in accordance with previous studies.6,,11,25,27–29

Although indoor and maternal smoking is traditionally not socially well acceptable in Russia,30 children were exposed regularly to high indoor and maternal smoking in Svetogorsk. The results are in line with a previous study that suggested that the highest smoking rates in Russia are found in areas, such as Svetogorsk, exposed to western influences and among young women 18–34 years of age, corresponding to the age range of mothers in the present study.31 The increase in the prevalence of smoking among women could be partly explained by a change in women's social position and especially in Russia the extensive marketing of tobacco products by the international tobacco companies.25,,32 Also increased prosperity in Svetogorsk due to foreign investments could explain these phenomena.

Inspite of printed and verbal information on health risks of the child related to tobacco smoke exposure distributed in maternity care in Finland,33,,34 a substantial proportion of women smoked during pregnancy and child's first year of life in Imatra. In addition, consistent with a previous study,35 smoking cessation seemed to be temporary and smoking returned to higher level soon after pregnancy. Because in Finland smoking among women during pregnancy has been strongly associated with low educational and socioeconomic status and young maternal age,27,,36 smoking cessation efforts are to some extent hampered by related problems, such as unemployment, physical or mental illnesses, and alcohol problems. This multi-problem group of smokers needs in the future a comprehensive supporting system, probably including a specifically tailored health promotion program and perhaps financial support.

The proportion of heavy smokers (≥15 cigarettes/day) was higher in Finland than in Russia among both parents. This finding is consistent with a previous study from Russia, but the prevalences were higher than in some previous studies from Finland.28,,37 The differences in the numbers of cigarettes smoked may be related to a greater amount of addictive and harmful substances in cigarettes and greater use of unfiltered cigarettes in Russia.38,,39 Although currently there are no marked differences in the tobacco legislation or restrictions between the two countries,40 differences in smoking behaviour of parents and children's exposure to ETS are considerable and can be probably explained by different cultural attitudes, and by poor enforcement of smoking legislations, extensive tobacco marketing and diminishing resources for health promotion in Russia.17,,25,39

Children's smoking

Smoking was more common among Russian children than Finnish children. Low smoking rates among school children in both countries compared to a previous study41 is probably explained by the age of subjects (>70% of participants were under 14 years of age). According to Pärna et al.,41 the mean age for starting smoking among Russian and Finnish adolescents was 13–14 years. Since questionnaires were filled in at home by the schoolchildren together with their parents, our study may have underestimated to some extent the true smoking rate.

Parental smoking and asthma

Our findings strengthen the evidence on the role of maternal smoking in pregnancy and early-life ETS exposure in the development of asthma.3,,6,21,29 The impact of maternal smoking was somewhat stronger than that of paternal smoking, probably because a larger proportion of cigarettes smoked by the mother are smoked in the vicinity of the child. In Finnish children, the effect estimates were somewhat higher for pre-natal and early-life exposures compared to school-age exposure. Consistently with a previous study from Finland,29 there was a clear exposure-response pattern, with no or relatively low risk in the low exposure categories, while the effects were usually substantial in the high exposure categories. There may be increased consciousness of the adverse effects related to passive smoking among parents and consequently, they may attempt to avoid exposing children, which would protect especially the children of light smokers.2 The children of heavy smokers are likely to be exposed to tobacco smoke in different types of situations as they are in the vicinity of smoking parents, even if the parents would try to avoid smoking at home.

There are only a few studies concerning the ETS exposure of children and its effects on allergic and respiratory diseases among Russian children.6,,9,11,26 In Russian children, the exposure to maternal smoking in pregnancy was rare and consequently, the effect estimates were imprecise. However, there was a trend of increased asthma in relation to tobacco smoke exposure in the child's first year of life and particularly related to current maternal smoking. Partly consistent with this study, Jaakkola et al.6 found that the risk of asthma was related to maternal smoking during pregnancy and early-life, although not to current ETS exposure among Russian school children.

Parental smoking and allergies

In Finnish children, the risk of any allergies was higher among children exposed to maternal smoking postnatally, with an exposure-response pattern. A similar trend was observed in Russian children for post-natal exposure and this was partly in line with a previous study from Russia.9

There are some studies looking at the relations between childhood ETS exposure and rhinitis,42 but only a few concerning childhood ETS exposure and rhinoconjunctivitis/conjunctivitis.11,,43 We found increased risk of allergic conjunctivitis in relation to child's exposure to maternal smoking during the first year of life and currently in Russia. A recent study from Italy found an elevated risk of conjunctivitis among ETS exposed women.43

Parental smoking and children's infections

There are some studies concerning the relations between childhood tobacco smoke exposure and upper respiratory infection,44 but we were not able to identify previous studies investigating childhood ETS exposure and common colds. Bensenor et al.45 showed that non-smoking women exposed to ETS were at increased risk of having more frequent and longer colds than those not exposed, which is consistent with our findings in Finnish children in relation to early life ETS. On the contrary, Biagini et al.42 observed that the prevalence of upper respiratory infections was highest in the non-ETS exposed group of infants, which would be consistent with our findings in the Russian children. At least part of these somewhat contradictory effect estimates for common cold/flu between countries could be explained by different exposure patterns and different diagnostic practices and labels.

Concluding remarks

This study showed that the time pattern of exposure to tobacco smoke differs substantially between the Finnish and Russian children, Finnish children having more exposure to maternal smoking during pregnancy and in infancy and Russian children having more exposure from paternal smoking and regular smoking indoors. The results indicate that parental smoking during and after pregnancy increase the risk of asthma and ETS exposure after pregnancy is related to common colds among school children in Finland, both outcomes showing an exposure-response pattern. In Russia, maternal smoking during infancy and currently increase the risk of allergic conjunctivitis. The results of this study suggest that more efforts should be directed to reducing parental smoking, with emphasis in Finland on maternal smoking during pregnancy and infancy and in Russia on paternal smoking and exposing children to tobacco smoke in general. Such actions should be emphazised in future educational health promoting programs and maternity and child care systems.

Acknowledgements

We thank senior lecturer Auli Rantio-Lehtimäki and Dr Kimmo Saarinen for their comments on the earlier draft, Dr Juha Jantunen for technical assistance in the illustration, Ms Seija Pohjalainen and Ms Tiia Sironen for assistance in data input and Ms Antonia Ieromnimon and Mr Reginald Quansah for statistical analyses. Statistical analyses were financially supported by the Päivikki and Sakari Sohlberg Foundation, planning of the study and acquisition of data were financially supported by Town of Imatra, European Union (South-East Finland Interreg III A –program) and Finnish Ministry of Foreign Affairs.

Conflict of interest: None declared.

Key points

  • The time pattern of exposure to tobacco smoke differs markedly between the Finnish and Russian children.

  • Maternal smoking during and after pregnancy increase the risk of asthma and common colds among school children in Finland, with an exposure-response pattern.

  • Maternal smoking increases the risk of allergic conjunctivitis among Russian children.

  • More efforts should be directed to reducing parental smoking, with emphasis in Finland on maternal smoking during pregnancy and infancy and in Russia on paternal smoking and exposing children to tobacco smoke in general.

References

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