Early onset of e-cigarette use and subsequent use frequency among US high school students

Objective: The aim of this study was to examine whether the age of e-cigarette use onset predicts subsequent use of e-cigarettes.

Methods: We used the National Youth Tobacco Survey (NYTS) from 2022. Our sample consisted of 4537 US high school students who had ever used e-cigarettes. Age of first e-cigarette use was assessed by a categorical variable ( $\le$ 12 years, 13 years, 14 years, 15 years, 16 years, and $\ge$ 17 years). We also constructed a binary variable of early onset use ( $<$ 14 years vs $\ge$ 14 years). E-cigarette use outcomes in the past 30 days included any use and frequent use (used on $\ge$ 20 days). Weighted multivariable logistic regressions were conducted for each outcome to assess the associations between early onset of e-cigarette use and subsequent use frequency, adjusting for a list of covariates.

Results: Among 4537 high school students who had ever used e-cigarettes, 49.5 % (95 % CI, 46.1 %-52.9 %) reported any use in the past 30 days and 22.8 % (95 % CI, 20.0 %-25.7 %) reported frequent e-cigarette use. Early-onset users, compared with those who tried e-cigarettes at age 14 or older, showed significantly higher risks of any use (aRR = 1.21, 95 % CI, 1.11-1.33) and frequent use (aRR = 1.88, 95 % CI, 1.60-2.20) in the past 30 days. We found younger age at first use to be associated with higher risk of current and frequent use.

Conclusions: Our findings highlight the importance for age-sensitive efforts, prioritizing younger adolescents, to prevent and delay e-cigarette use initiation.