Table 1

Characteristics of included studies

Study nameStudy designEligibility criteriaCharacteristics of participantsExposureOutcomesResultsGovernance
Watkins 201821 Prospective cohort (PATH* study)
  • Wave 1: September 2013 to December 2014.

  • Wave 2: October 2014 to October 2015.

US youth (12–17 years) who reported never having smoked a cigarette in wave 1.10 384 participants; mean age=14.3 (SD 1.7); 49% female; 53% white
Ever hookah users: 3.3%
Past 30-day hookah users: 0.6%.
Ever use and past 30-day use of hookah at baseline.
  • Ever use of cigarettes at 1 year.

  • Past 30-day use of cigarettes at 1 year.

  • Ever cigarette use: adjusted OR (ever vs never users of hookah at baseline): 1.79 (95% CI 1.23 to 2.62).

  • Ever cigarette use: adjusted OR (past 30-day users vs never users of hookah at baseline): 2.58 (1.20 to 5.55).

  • Past 30-day cigarette use: adjusted OR (ever users vs never users of hookah at baseline): 1.92 (95% CI 1.17 to 3.17).

  • Past 30-day cigarette use: adjusted OR (past 30-day users vs never users of hookah at baseline): 2.69 (0.91 to 7.98).

Funding:
  • US National Cancer Institute.

  • Food and Drug Administration Center for Tobacco Products.

  • National Institute on Drug Abuse.

  • US National Center for Advancing Translational Science.


COI: ‘none reported’
Jaber 20159 18 29 Longitudinal study
3-year follow-up.
Seventh grade students in 19 randomly selected schools, out of a total of 60 schools in the city of Irbid, Jordan. Students reported at baseline never having smoked cigarettes.1454 students
Mean age=12.6 (SD 0.61); 45.3% males;
298 (20.5%) waterpipe-only smokers.
Ever waterpipe use.Ever cigarette use at 3 years.Ever cigarette use: adjusted HR (ever vs never waterpipe use): 1.67 (95% CI 1.46 to 1.92).
The risk of initiating cigarette smoking increased with the frequency of waterpipe smoking.
Funding:
  • National Institute on Drug Abuse.


COI: ‘none declared’
Soneji 201519 Longitudinal study
  • Wave 1: October 2010 to June 2011.

  • Wave 2: October 2012 to March 2013.

Individuals aged 15–23 years old from the USA
Baseline non-cigarette smokers.
2541 participants
20.1% smoked waterpipe tobacco.
Waterpipe tobacco smoking.
  • Cigarette smoking initiation at 2 years.

  • Current cigarette smoking (within past 30 days) at 2 years.

  • The intensity of cigarette smoking at 2 years.

  • Cigarette smoking initiation: adjusted OR (users vs never users of waterpipe at baseline): 2.56 (95% CI 1.46 to 4.47).

  • Current cigarette smoking (within past 30-day): adjusted OR (users vs never users of waterpipe at baseline): 2.48 (95% CI 1.01 to 6.06).

  • Higher intensity of smoking at 2 years follow-up: adjusted Proportional OR (users vs never users of waterpipe at baseline): 2.55 (95% CI 1.48 to 4.38).

Funding
  • National Cancer Institute.

  • National Centre for Advancing Translational.


COI: none reported
Fielder 201322 Prospective Study
August 2009 to August 2010
American first-year female college students
At least 18 years of age.
424 first-year college women
Median age=18.1 old; 67% White
Hookah tobacco use precollege: 28%.
Ever smoked hookah before starting college.Cigarette smoking initiation at 8 months.Cigarette smoking initiation: adjusted OR: 1.08 (95% CI 1.02 to 1.15).Funding:
  • The National Institute on Alcohol Abuse and Alcoholism.


COI: ‘no conflicts of interest’
Treur 201720 Cohort StudyDutch adolescents from two cohorts.From cohort I: 2100 included participants (aged 11–17 years)
Ever waterpipe users: 15%
Past month waterpipe users: 7%.
Ever use of waterpipe.Ever conventional cigarette smoking at 6 months.
  • Ever conventional cigarette smoking in cohort I (ever vs never users of waterpipe at baseline): unadjusted OR 5.36 (95% CI 2.78 to 10.31).

Funding:
  • The European Research Council, Netherlands Organisation for Health Research and Development.

  • National Institute for Public Health and the Environment.


COI: not reported
Creamer 201813 Longitudinal Study
Wave 1 (November 2014 to February 2015)
Wave 2 (6 months later)
Started in fall 2014.
US students attending one of 24 2-year and 4-year colleges in Texas and involved in the first two waves of the Marketing and Promotions Across Colleges in Texas Project (Project M-PACT) were recruited to participate in the online survey via email invitation.4321 participants
18–29 years old (mean age at wave 1=20.49; SD=2.36) and more than half were female (63.4%)
Previous month waterpipe users: 11.50%.
Past 30 day use of hookah.Current use of cigarettes (within past 30 days) at 6 months.Current cigarette smoking (within past 30-day): adjusted OR (past 30-day users vs never users of hookah at baseline): 2.43 (1.68 to 3.52).Funding:
  • The National Cancer Institute and the FDA Centre for Tobacco Products (CTP).


COI: not reported
  • *PATH (Population Assessment of Tobacco and Health) is a national longitudinal cohort study of 45 971 adults and youth 12 years of age and older. The PATH youth sample consists of individuals whose parents were sampled for the PATH adult survey.

  • †Project M-PACT is a rapid response surveillance study that includes a cohort of 5482 college students who were 18–29 years old at wave 1 (November 2014 to February 2015). Of the 5482 students, 79% participated 6 months later at wave 2 (n=4326), but 30 had missing data used in models in the present study.