Longitudinal association between environmental tobacco smoke exposure and behavioral problems in children from ages 5 to 9.

Few studies have assessed the cumulative effects of exposure to environmental tobacco smoke (ETS) in relation to children's neurobehavioral problems over time. We assessed the longitudinal associations between ETS exposure at age 5 and behavioral problems at ages 5, 7, and 9 using the Ewha Birth and Growth Cohort, in Seoul, Korea. Children with available urinary cotinine levels at age 5 and one or more behavioral problem scores measured with the Korean Version of Child Behavior Checklist (CBCL) at age 5, 7, and 9 were included in the study. Those whose mothers smoked during pregnancy were excluded, and a total of 179 children were included in the analysis. A linear mixed-model analysis using a REPEATED statement was conducted to assess whether ETS exposure was associated with the total, internalizing, and externalizing behavioral problem scores of the CBCL. The group with higher levels of cotinine showed continuously higher total and external behavioral problem scores from ages 5 to 9, which was seen after adjusting for preterm birth, father's education level, and television watching time. In addition, the difference in the total and external behavioral problem scores between the higher and lower cotinine groups at age 5 was statistically significant after a Bonferroni correction (p = 0.02 and 0.04, respectively), even though the fixed effect of cotinine level was almost but not statistically significant (p = 0.07 and 0.08, respectively). The results of this longitudinal cohort study provide evidence regarding the negative effects of ETS exposure in early childhood and their behavioral problems over time. This study supports the strengthening of anti-smoking policies used in educational interventions for parents, in order to reduce early ETS exposure in children.