Association between children's secondhand co-exposure to tobacco and cannabis smoke and elevated urinary cotinine levels: a cross-sectional analysis.

Background: Cannabis use is far more common among adults who smoke tobacco than adults who do not, and its use is increasing among people who smoke tobacco with children living in the home. Given the well-established evidence that caregiver smoking is the primary source of children's secondhand exposures to these products, the increasing trend in caregiver co-use is raising public health concerns about children's co-exposure. Emerging data indicates that adult co-use is linked to additive health consequences, such as elevated nicotine and other tobacco-related toxicant blood levels, relative to use of only tobacco. It is unknown whether children's co-exposure leads to similar additive consequences. This study examined whether children's co-exposure to secondhand tobacco and cannabis smoke related to higher urinary levels of cotinine (the primary nicotine metabolite) relative to children exposed to only tobacco smoke. Methods: This study performed a cross-sectional analysis of baseline data from the 'Babies Living Safe and Smokefree' tobacco intervention randomised controlled trial. All participants (N=396) included low-income mothers who smoked tobacco daily and were primary caretakers of young children (<6 years old). Multivariable regression was performed to test the hypothesis that maternal co-smoking would relate to children's elevated cotinine levels in a model including potential confounding variables (eg, children's mean daily tobacco smoke exposure, maternal nicotine dependence level). Results: Mean participant age was 30.11+6.52 years old, and their children's age was 30.24+20.0 months old. In the past 7 days, 146 (36.9%) participants reported smoking cannabis on at least 1 day. Multivariable regression modelling showed that maternal co-smoking was associated with higher children's cotinine levels (p=0.04). Conclusions: Maternal co-use of tobacco and cannabis, relative to tobacco smoking only, is associated with higher cotinine levels in their children. Given that caregiver smoking is the primary source of young children's exposure to both tobacco and cannabis, clinicians and the public could be better informed about the potential additive health risks of co-exposure without diluting existing health messaging and prevention efforts focused on use and exposure risks related to each product independently. Results point to the need for sustained public health efforts to reduce children's exposure to these toxicants.