Thirty-day smoking in adolescence is a strong predictor of smoking in young adulthood.

Thirty-day smoking, although a widely used measure of adolescent smoking (age 12-16), has been questioned as an accurate measure of young adult (age 26-30) smoking behavior, particularly when critiquing studies linking use of e-cigarettes with subsequent cigarette smoking. We used logistic regression to test two measures of 30-day adolescent smoking as predictors of young adult smoking in the National Longitudinal Survey of Youth 1997. Adjusting for psychosocial covariates, compared to those who smoked zero days in the past 30 days in adolescence, odds of any past-30-day smoking in young adulthood ranged from 2.85 (95% CI: 1.85-4.37) for those who smoked 1 day to 4.81 (3.50-6.59) for those who smoked daily as adolescents, and adjusted odds of daily smoking in young adulthood ranged from 1.99 (1.24-3.18) to 4.69 (3.42-6.43). Compared with adolescent never smokers, adjusted odds of any past-30-day smoking in young adulthood among adolescent former smokers was 2.11 (1.77-2.53), and among adolescent current smokers, ranged from 3.03 (2.22-4.14) for those who smoked 1-5 cigarettes per month to 8.19 (5.80-11.55) for those who smoked daily. Adjusted odds of daily smoking in young adulthood were 2.49 (2.12-2.91) for adolescent former smokers and, among adolescent current smokers, ranged from 2.54 (1.92-3.37) for those who smoked 1-5 cigarettes per month to 8.65 (6.06-12.35) for those who smoked daily. There is a strong dose-response relationship between 30-day smoking in adolescence-even a single day in the month-and 30-day and daily smoking in young adulthood.