Introduction There is a concern that waterpipe tobacco smoking (WTS) can lead to the later initiation of cigarette smoking, a concept referred to as the ‘gateway theory’. The objective of the study was to systematically review the literature for the association of WTS with later initiation of cigarette smoking.
Methods We searched Medline, Embase and ISI Web of Science in April 2018 without using any language or date restrictions. We selected eligible studies, abstracted data and assessed the risk of bias using a duplicate and independent approach. We meta-analysed the ORs across eligible studies using the inverse variance method and the random-effects model. We assessed the certainty of evidence using the Grading of Recommendations Assessment, Development and Evaluation methodology.
Results We included eight papers reporting on six eligible prospective cohort studies with a total of 21 224 participants, belonging to the adolescent and young adult age categories. The pooled adjusted OR for the association between ever waterpipe user (compared with never waterpipe user) at baseline, with ‘cigarette smoking initiation’ (ever cigarette use) was 2.54 (95% CI 1.60 to 4.02) at 6 months to 3 years follow-up (moderate certainty evidence). The pooled adjusted OR for the association between ever waterpipe user (compared with never waterpipe user) at baseline, with ‘current cigarette smoking’ (past 30-day cigarette use) was 2.04 (95% CI 1.32 to 3.15) at 1–2 years follow-up (moderate certainty evidence). The pooled adjusted OR for the association between past 30-day waterpipe user (compared with never waterpipe user) at baseline, with current cigarette smoking (past 30-day cigarette use) 2.46 (95% CI 1.73 to 3.49) at 6 months to 1 year follow-up (high certainty evidence).
Conclusion Our findings indicate that WTS is associated with more than doubling of the odds of later initiation of cigarette smoking, supporting the gateway theory. Strengthening WTS policies is a priority and further research is needed on the development and evaluation of appropriate clinical and public health interventions.
- non-cigarette tobacco products
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Contributors EA and DA contributed to the study conception and design. DA developed the search strategy. DA and MJ contributed to the screening of articles and the acquisition of the data from the selected studies. Together DA, MJ, and EA contributed to the analysis and interpretation of data. DA and EA drafted the manuscript. DA, MJ, EA contributed to the critical revision and the final version of the manuscript. EA, the corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
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