Elsevier

Drug and Alcohol Dependence

Volume 147, 1 February 2015, Pages 103-108
Drug and Alcohol Dependence

Maternal and paternal indoor or outdoor smoking and the risk of asthma in their children: A nationwide prospective birth cohort study

https://doi.org/10.1016/j.drugalcdep.2014.12.001Get rights and content

Highlights

  • We examine the association between parental indoor smoking and childhood asthma.

  • Parental indoor smoking at home increased and exacerbated children's asthma.

  • Attributable fraction to both parents smoking indoors was large for childhood asthma.

  • Smoking at home, whether it is indoors or outdoors, may increase the risk for childhood asthma.

Abstract

Background

Little is known about the differential impact of combinations of parental smoking behavior (indoor or outdoor smoking, or not smoking) on preventing childhood asthma. Our objective was to examine the association between parental smoking behavior and children's asthma.

Methods

A nationally representative population-based birth cohort of 40,580 babies, aged 0.5 years in 2001 (response rate, 87.8%), was studied to estimate adjusted odds ratios of combinations of maternal and paternal indoor or outdoor smoking at home for physician visits and hospitalization for childhood asthma up to 8-years-old, and population attributable fractions.

Results

Odds of hospitalization for asthma among children whose father alone smokes indoors at home did not largely increase (up to 20%). However, if the mother also smokes indoors at home, the odds strongly increased. After adjusting for demographic, perinatal and socioeconomic factors, the increase in odds for children whose father and mother both smoke indoors compared to children with non-smoking parents was 54% (95% confidence interval: 21–96%), 43% (8–90%) and 72% (22–143%) for children aged 0.5 < −2.5, 2.5 < −4.5 and 4.5 < −8 years-old, respectively. The odds ratios of smoking outdoors did not largely differ from those of smoking indoors. Our estimation of population attributable fractions revealed that if all parents in Japan quit smoking, hospitalization of children for asthma could be reduced by 8.3% (2.2–14.3%), 9.3% (0.9–17.6%) and 18.2% (7.7–28.8%), respectively.

Conclusions

Parental indoor smoking at home increased and exacerbated children's asthma. Smoking at home, whether it is indoors or outdoors, may increase the risks for asthma attacks of their children.

Introduction

Children are likely to be exposed to second hand tobacco smoke (SHS) at home (U.S. Department of Health and Human Services [USDHHS], 2006). A study in Japan has shown that 64.8% of 6-month old children live with smoking parent(s), and of those, 57.9% of parents smoke indoors at home (Kaneita et al., 2006). Although many previous studies have revealed the risk of SHS for childhood asthma (Royal College of Physicians, 2010, U.S. Department of Health and Human Services, 2006), a recent review by Burke et al. (2012) showed several evidence gaps in this field of research. There has been no prospective study of the risk of paternal smoking for asthma in children aged 2 years or less and only one study for children aged 3–4 years. Further, a wide range of estimated effect size of postnatal maternal smoking on incidence of childhood asthma was observed, indicating a need to confirm the results. One objective of our study was to approach these gaps. A previous study by Kanoh et al. (2012), using data from the Longitudinal Survey of Newborns in the 21st Century, reported a positive hazard risk between parental smoking and childhood asthma incidence. However, they did not focus on the gaps (i.e., did not use corresponding age categories) and did not use severity of asthma as an outcome. Furthermore, although parents are encouraged to smoke outdoors or not to smoke (Committee on Substance Abuse, 2001), the difference in the contribution of these parental smoking behaviors to the risk reduction of asthma among their children has not been sufficiently evaluated (Blackburn et al., 2003, Blizzard et al., 2003, Leung et al., 2004). Thus, the main objective of this study was to assess whether and how parental smoking behaviors, combined with indoor smoking status at home, were associated with the development and severity of childhood asthma from very young ages to 8 years old, using data from a large nationally representative birth cohort study.

Section snippets

Study population

The data used for this study were taken from the Longitudinal Survey of Newborns in the 21st Century which was conducted by the Japanese Ministry of Health, Labour, and Welfare from 2001 to 2009 (Ministry of Health, Labour and Welfare, 2013). The study sample included all infants born in Japan during the periods January 10–17, 2001, and July 10–17, 2001 using the national birth record (n = 53,575). Questionnaires were mailed when the infants were 0.5 years of age. The total number of respondents

Results

The baseline characteristics of study subjects according to the parental smoking categories are shown in Table 2. All covariates except for child's sex show statistically significant differences; i.e., maternal smoking groups showed lower birthweight, less exclusive breastfeeding, younger parental age, and lower equivalent household income.

The prevalence of outcomes within defined time durations are shown in Table 3 (numbers in Supplementary Table 25

Discussion

Using Japanese nationally representative large cohort data, we found an elevated association with asthma among the children who were exposed to SHS from parental smoking. This is consistent with the findings of preceding studies in Japan and other areas (USDHHS, 2006). The primary new findings of the present study were, (i) compared to children whose parents do not smoke tobacco, children whose parents smoke indoors at home showed increased association with having asthma in terms of both

Role of funding source

This study was supported by the Ministry of Health, Labour and Welfare (Grant; Comprehensive Research on Life-Style Related Diseases including Cardiovascular Diseases and Diabetes Mellitus (H25-010)), and the Ministry of Education, Culture, Sports, Science and Technology (Grant; Scientific Research on Innovative Areas KAKENHI 21119003). The funding sources had no role in the design and conduct of the study; the analysis and interpretation of the data; or the preparation, review, or approval of

Contributors

All authors contributed to and have approved the final manuscript.

Conflict of interest statement

All authors declare that they have no conflicts of interest.

Acknowledgments

We thank Dr Takahiro Hoshino, Dr Yuri Ito and Dr Jun Ito for their assistance in database formation, statistical methods and valuable comments. We also thank Dr Julia Mortimer for her English language editing.

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    Supplementary material can be found by accessing the online version of this paper at http://dx.doi.org and by entering doi:10.1016/j.drugalcdep.2014.12.001.

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