1. In this meta-analysis of available studies about youths’ use of e-cigarettes was associated with increased risk of initiation for cigarette smoking and past 30-day history of smoking.
2. Risk of smoking linked to e-cigarette use remained an independent risk factor when accounting for known confounders; but there existed a moderate degree of heterogeneity in study quality.
Evidence Rating Level: 1 (Excellent)
Study Rundown: E-Cigarette use has led to concerns that it may contribute to tobacco smoking. While some studies have shown benefit as a possible smoking cessation aid to reduce nicotine cravings, there is concern that it may increase smoking amongst non-smoking adolescents. Many current laws regulating tobacco advertising to children do not include e-cigarettes and levels of nicotine can vary widely between products. The current study was a meta-analysis of available studies aimed to quantify risk of initiation of cigarette smoking that could be attributed to e-cigarettes. The study found a significantly increased risk of cigarette smoking among users of e-cigarettes compared to never users.
The magnitude of the effect of e-cigarettes on tobacco smoking was comparable to known risk factors, such as parental and peer smoking. The main limitations of the study included the high rate of loss-of-follow-up in many of the studies, and the lack of data on the types of e-cigarette products used as the nicotine levels can vary between different products.
In-Depth [meta-analysis]: This study included a systematic review of literature and included studies that evaluated e-cigarette use and risk of starting smoking during a follow-up period, or studies that looked at past 30-day use of e-cigarette use and development of past 30-day cigarette smoking in follow up. Cross sectional studies without temporal association were excluded. Known covariates were included for the analysis: parental, sibling, and peer cigarette use, risk taking behavior, substance use, delinquent behavior, depressive symptoms, and sensation seeking behavior.
A total of 9 studies were included in the analysis which together encompassed 16 621 adolescents and young adults (ages 14 to 30 years-old). In multivariate regression analysis, use of e-cigarettes was associated with an odds ratio of 3.62 (95%CI 2.42-5.41) for cigarette smoking initiation. The multivariate analysis for development of past 30-days cigarette smoking at follow up had an odds ratio of 4.28 (95%CI 2.52-7.27) linked to e-cigarette use. There was moderate heterogeneity of included studies; with 6 of the 9 included studies having greater than 20% rate of loss-of-follow-up.
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