Associations between parental smoking and teenage alcohol and drug use in the Growing Up in Ireland cohort study: a longitudinal observational study.

Background: Children with a parent who smokes are more likely to become substance users than those who do not have a parent who smokes. In this study, we examined whether childhood or early adolescent exposure to primary parent smoking increased the risk of subsequent teenage alcohol and drug use at ages 17-18 years.
Methods: For this longitudinal observational study, we analysed data from 6039 teenagers and their parents from the waves 1-3 of the Growing up in Ireland Cohort 98' Study. Parental smoking was assessed at baseline (9 years) and wave 2 (13 years) with responses coded as yes or no. The primary parent was defined as the person who provided most care and who knew most about the Study Child, usually the mother or mother figure for 98% of study participants. Teenage alcohol and drug use assessed at ages 17-18 years (wave 3) was determined by responses to the question "Have you ever consumed alcohol?" (answers yes or no), drug use was assessed by questions on ever trying aerosols/gas, cannabis, and non-prescribed drugs, with those answering yes being classified as other-drug ever users. We did a logistic regression analysis to examine the associations between parents' smoking on teenage alcohol and drug use, controlling for covariates: gender, education, income, education, region, and household type. Ethics approval for the GUI project was obtained from the Health Research Board.
Findings: Of the 6039 teenagers included in our study, 2968 (49%) were female, 3070 (51%) were male, 5351 (89%) ever used alcohol, 5065 (85%) were current users, and 2098 (35%) used other drugs. Rates of primary parent smoking were 31% (n=1883) in wave 1 and 30% (n=1829) in wave 2. After adjusting for other exposures known to be associated with teenage substance use, primary parent smoking at waves 1 and 2 was associated with higher odds of teenage alcohol ever use (adjusted odds ratios [aORs] 1·89 [95% CI 1·44--2·46] at wave 1 and 1·53 [1·20-1·98] at wave 2), current alcohol use (1·88 [1·50-2·36] and 1·59 [1·28-1·97]) and other-drug ever use (1·699 [1·45-1·95] and 1·71 [1·47-1·98]).
Interpretation: Teenagers aged 17-18 years exposed at ages 9 and 13 years to parental smoking were more likely to report significantly higher odds of alcohol and drug use at age 17-18 years. The finding that exposure to parent smoking in childhood increases the risk of teenage alcohol and other drug use suggests a need for interventions aimed at parents who smoke Limitations include potential unmeasured or residual confounders and reliance on self-reported teenage substance use behaviours.
Funding: Royal City of Dublin Hospital Trust, Irish Research Council Government of Ireland Postgraduate Scholarship Programme.
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