Secondhand tobacco exposure assessed using urinary cotinine among 10 years children in Japan: A 11-years repeated cross-sectional study

Introduction The emergence of heated tobacco products (HTPs) has complicated the issue of secondhand tobacco (SHT) exposure. We investigated the trend in SHT exposure in schoolchildren and assessed whether SHT exposure depends on household tobacco use status. Methods This repeated cross-sectional study from 2011 to 2021 (15,927 subjects were eligible) was based on data from an annual survey of fourth-grade students (aged 10 years) in Kumagaya City, located in Kanto Region, Japan. Data were collected by questionnaire, and urinary cotinine levels used as an objective indicator of SHT exposure, such as secondhand exposure to combustible cigarette (CC) smoke and HTP-generated aerosols. Results SHT exposure has decreased by about one-quarter over the 11-year period, from 18.6% in 2011 to 5.3% in 2021. Regarding household tobacco product use, 68.1% did not use tobacco products, 16.5% were CC-only users, 12.3% were HTP-only users, and 3.0% were both CC and HTP users. The prevalence of SHT exposure among participants was significantly higher compared to participants with no tobacco product users in the household, in the following order: both CC and HTP users, only CC users, and only HTP user. Conclusions While the prevalence of SHT exposure showed a decreasing trend during 2011-2021, the prevalence of SHT exposure was higher in schoolchildren from families with tobacco product users than in schoolchildren from families without tobacco product users, regardless of the type of tobacco product.