Smoking trajectories from adolescence to early adulthood as a longitudinal predictor of mental health in adulthood: evidence from 21 years of a nationally representative cohort.

Aims: To measure the prospective relationship between smoking trajectories from adolescence to young adulthood and mental health in later adulthood and test whether this relationship was mediated by concurrent co-use of alcohol and marijuana.

Design: Longitudinal study using data drawn from rounds 1 to 18 of the National Longitudinal Survey of Youth 1997 (NLSY97), a nationally representative cohort study spanning 21 years.

Setting: United States.

Participants: The analytical sample included those who completed survey items about smoking behaviors on at least half the data collection opportunities in adolescence and young adulthood (n = 8570, 48.9% female, 66.2% white).

Measurements: Mental health in adulthood was measured using the five-item Mental Health Inventory (MHI-5; range = 0-100) at round 18. Seven trajectories of smoking from adolescence to young adulthood were identified by group-based multi-trajectory modeling, using data over 11 years from rounds 1 to 11.

Findings: Late-onset moderate smokers [β = -1.95, 95% confidence interval (CI) = -3.61 to -0.29], late-onset accelerated smokers (β = -2.53, 95% CI = -4.28 to -0.78), early-onset heavy smokers (β = -3.72, 95% CI = -5.59 to -1.85) and early-onset moderate smokers (β = -2.66, 95% CI = -4.48 to -0.84) showed poorer regression-adjusted mean MHI-5 scores in later adulthood than stable abstainers, even after controlling for baseline mental health and covariates. Whether or not a difference in MHI-5 scores was present between quitters and stable abstainers was inconclusive. The concurrent co-use of alcohol and marijuana in young adulthood significantly mediated the relationship between smoking trajectory and mental health.

Conclusions: Continued smoking, especially early-onset and heavy smoking from adolescence to young adulthood, appears to increase the risk of poor mental health later in mid-adulthood, and quitting smoking in young adulthood may mitigate such risk even among early-onset smokers. Mediation analyses underscore the role of using multiple substances in this pathway.