In the process of investigating the decline in adolescent smoking, we came across some unexpected findings with important implications for preventing smoking uptake and reducing health disparities.
As in many other countries, ethnic disparities in smoking prevalence are pronounced in New Zealand. For example, in 2014 13% of Māori (indigenous) Year 10 students (aged 14-15) smoked monthly or more often, compared to 4% of non-Māori. The Māori population has a youthful structure (making up quarter of NZ’s secondary school population but only 15% of the general population) so preventing smoking in adolescents is an important strategy for reducing tobacco-related harm in Māori as a whole.
To inform prevention efforts, we investigated exposure to and relative importance of known predictors of adolescent smoking (parental, sibling and peer smoking, and exposure to smoking in the home) and how these have changed over time, for Māori and adolescents overall.
Previous research has shown that exposure to smoking by other people in the home environment increases adolescents’ likelihood of becoming smokers themselves. This may be due to a physiological ‘priming’ effect on neural nicotine receptors, as well as socialisation.
We used repeat cross-sectional data, 2003–2015, from a national survey of Year 10 students (N = 20,443 – 31,696 per year). For the overall sample and for Māori and non-Māori, we calculated adjusted odds ratios (OR) to assess the association between adolescent smoking and risk factors each year: one or more parents smoke, best friend smokes, older sibling(s) smoke, and past week exposure to smoking in the home. We calculated population attributable risk (PAR, a measure that combines prevalence of exposure and strength of association) for risk factors in 2003 and 2015.
Exposure to smoking in the home became a stronger risk factor for adolescent smoking over time, independent of parental and sibling smoking, particularly for Māori. Between 2003 and 2015, adjusted ORs for exposure to smoking in the home increased from 1.7 to 2.6 for the overall sample, and from 1.8 to 3.4 for Māori. The PAR for exposure to smoking in the home approximately doubled for both groups, while PARs for the other risk factors decreased.
Teens growing up in smokefree homes were less likely to smoke, even if their parents were smokers. After adjusting for other risk and demographic factors in the model, parental smoking was a weak or non-significant risk factor.
Reducing adolescents’ exposure to smoking in the home (e.g. by promoting smokefree homes) is likely to reduce adolescent smoking uptake, with differentially positive effects on Māori. It will also have direct health benefits.
Many of the harms to the next generation are preventable by ‘taking the smoke outside’, even when parents continue to smoke. This may be an empowering message for parents who struggle to quit, but want to do their best for their children.
The extent to which these findings are generalizable to other countries is unknown, but our research suggests that exposure to smoking in the home deserves more research and policy attention internationally.
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