title: 'Only Fathers Smoking' Contributes the Most to Socioeconomic Inequalities: Changes in Socioeconomic Inequalities in Infants' Exposure to Second Hand Smoke over Time in Japan.
abstract: BACKGROUND
  Exposure to second hand smoke (SHS) is one of the major causes of premature death and disease among children. While socioeconomic inequalities exist for adult smoking, such evidence is limited for SHS exposure in children. Thus, this study examined changes over time in socioeconomic inequalities in infants' SHS exposure in Japan.
  
  
  METHODS
  This is a repeated cross-sectional study of 41,833 infants born in 2001 and 32,120 infants born in 2010 in Japan from nationally representative surveys using questionnaires. The prevalence of infants' SHS exposure was determined and related to household income and parental education level. The magnitudes of income and educational inequalities in infants' SHS exposure were estimated in 2001 and 2010 using both absolute and relative inequality indices.
  
  
  RESULTS
  The prevalence of SHS exposure in infants declined from 2001 to 2010. The relative index of inequality increased from 0.85 (95% confidence interval [CI], 0.80 to 0.89) to 1.47 (95% CI, 1.37 to 1.56) based on income and from 1.22 (95% CI, 1.17 to 1.26) to 2.09 (95% CI, 2.00 to 2.17) based on education. In contrast, the slope index of inequality decreased from 30.9 (95% CI, 29.3 to 32.6) to 20.1 (95% CI, 18.7 to 21.5) based on income and from 44.6 (95% CI, 43.1 to 46.2) to 28.7 (95% CI, 27.3 to 30.0) based on education. Having only a father who smoked indoors was a major contributor to absolute income inequality in infants' SHS exposure in 2010, which increased in importance from 45.1% in 2001 to 67.0% in 2010.
  
  
  CONCLUSIONS
  The socioeconomic inequalities in infants' second hand smoke exposure increased in relative terms but decreased in absolute terms from 2001 to 2010. Further efforts are needed to encourage parents to quit smoking and protect infants from second hand smoke exposure, especially in low socioeconomic households that include non-smoking mothers.
authors.affiliation: Department of Community and Global Health, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Saito
authors.affiliation: Center for Cancer Control and Statistics, Osaka Medical Center for Cancer and Cardiovascular Diseases, 3-3 Nakamichi 1-chome, Higashinari-ku, Osaka, 537-8511, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Tabuchi
authors.affiliation: Department of Community and Global Health, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Shibanuma
authors.affiliation: Department of Community and Global Health, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Yasuoka
authors.affiliation: Health Promotion Research Center, Institute of Community Medicine, Japan Association for Development of Community Medicine, Todofuken Kaikan Bldg, 15th Floor, 2-6-3 Hirakawa-cho, Chiyoda-ku, Tokyo, 102-0093, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Department of Community and Global Health, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
authors.forename: Masamine
authors.initials: M
authors.lastname: Jimba
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D005191:Family Characteristics; D005220:Fathers; D005260:Female; D006801:Humans; D007182:Income / Q000706:statistics & numerical data; D007564:Japan; D008297:Male; D012907:Smoking / Q000009:adverse effects*; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires; D014026:Nicotiana / Q000009:adverse effects; D014028:Tobacco Smoke Pollution / Q000706:statistics & numerical data*; D055815:Young Adult
chemical_list: D014028:Tobacco Smoke Pollution