Abstract
Evidence on behavioural abnormalities in children exposed to secondhand smoke is limited. This study examined the relation between infant/ toddler cotinine concentration, a biomarker of secondhand smoke exposure, and behavioural problems in preschoolers who were unexposed to maternal smoking during gestation. A prospective cohort of 301 non-smoking mothers with their young children aged ≤18 months visiting postnatal primary care clinics in Hong Kong was enrolled in 2012 and followed by telephone survey 3 years afterwards. Saliva was collected at baseline for cotinine assay. Child behavioural health at 3-year follow-up was assessed by the parent-reported Strengths and Difficulties Questionnaire (SDQ). We conducted multivariable linear regressions to compute regression coefficients (b) of SDQ scores in relation to salivary cotinine level. Mean ± SD age of children at follow-up was 3.7 ± 0.5 years and 50.8% were boys. After adjusting for age, sex, birthweight, household income, housing type, maternal education and depressive symptoms, greater cotinine concentrations during early childhood were associated with greater conduct problems (b = 0.90, 95% CI 0.03–1.76) and hyperactivity/ inattention (b = 1.12, 95% CI 0.07–2.17) at preschool age. This study corroborates previous findings on the potential role of secondhand smoke in development of child behavioural problems.
Highlights
Despite growing literature on the associations of secondhand smoke (SHS) exposure with behavioural problems in children, evidence is inadequate to infer causality[1,2]
The present study analysed data collected from 301 mother-infant dyads who completed the Strengths and Difficulties Questionnaire (SDQ), which was included in the follow-up questionnaire as an optional component
Only 3.1% of mothers (8/ 253) were found to have salivary cotinine concentrations of ≥12 ng/ml. Exclusion of their children from the regression analyses (Model 3) did not change the observed associations of cotinine concentration with conduct problems (b = 1.05, 95% CI 0.09 to 2.02) and hyperactivity/ inattention (b = 1.17, 95% CI 0.12 to 2.22). This is the first study prospectively examining the association of SHS exposure with child behavioural problems using an objective biomarker of SHS exposure
Summary
Despite growing literature on the associations of secondhand smoke (SHS) exposure with behavioural problems in children, evidence is inadequate to infer causality[1,2]. Many studies were limited by suboptimal control for maternal smoking during pregnancy (MSP)[5], which may have independent effect on child behavioural problems[6]. It is challenging to separate the effect of postnatal SHS exposure from MSP on child health outcomes since mothers who smoked during pregnancy are likely to continue smoking postnatally[2]. We were not aware of any study on SHS exposure in children aged ≤18 months, who typically reside at home most of the time, and subsequent risk of behavioural problems. Using a prospective cohort of young children whose mothers were non-smokers in Hong Kong, we examined the association of SHS exposure during early childhood with behavioural health at preschool age
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