Adolescent electronic cigarette use and tobacco smoking in the Millennium Cohort Study.
AIMS
To evaluate the catalyst, diversion and common liability hypotheses by examining associations between e-cigarette use and tobacco cigarette smoking at modal ages 14 and 17 years, controlling for adolescent and infancy risk factors.


DESIGN
Intergenerational, prospective cohort data from the Millennium Cohort Study (MCS). Nationally representative sample of infants born September 2000 to January, 2002.


SETTING
United Kingdom.


PARTICIPANTS
Parent and child data from 10 625 youth assessed in infancy and modal ages 11, 14 and 17 years.


MEASUREMENTS
Age 14 and 17 e-cigarette and combustible cigarette use (recency, frequency). Potential confounders were age 11 risk factors (e.g. alcohol use, externalizing behaviors, parental tobacco use, permissiveness), infancy risk factors (e.g. maternal smoking during pregnancy, smoke exposure in infancy) and demographic characteristics.


FINDINGS
Among youth who had not smoked tobacco by age 14 (n = 9046), logistic regressions estimated that teenagers who used e-cigarettes by age 14 compared with non-e-cigarette users, had more than five times higher odds of initiating tobacco smoking by age 17 [odds ratio (OR) = 5.25, 95% confidence interval (CI) = 3.28-8.38] and nearly triple the odds of being a frequent tobacco smoker at age 17 (OR = 2.91, 95% CI = 1.56-5.41), net of risk factors and demographics. Among youth who had not used e-cigarettes by age 14 (n = 9078), teenagers who had smoked tobacco cigarettes by age 14 had three times higher odds of initiating e-cigarettes by age 17 (OR = 2.98, 95% CI = 1.74-5.09) compared with non-tobacco smokers and nearly three times higher odds of frequently using e-cigarettes at age 17 (OR = 2.90, 95% CI = 1.21-6.95), net of confounders. Similar links between e-cigarette and tobacco cigarette use were observed in regressions following coarsened exact matching.


CONCLUSIONS
E-cigarette use by age 14 is associated with increased odds of tobacco cigarette initiation and frequent smoking at age 17 among British youth. Similarly, tobacco smoking at age 14 is associated with increased odds of both e-cigarette initiation and frequent use at age 17.
['Staff|Jeremy|J|https://orcid.org/0000-0003-0939-2250', 'Kelly|Brian C|BC|https://orcid.org/0000-0003-2039-1347', 'Maggs|Jennifer L|JL|', 'Vuolo|Mike|M|https://orcid.org/0000-0002-2916-0046']
millennium cohort study Catalyst common liability E-cigarette use tobacco use coarsened exact matching youth smoking