Differences in time to onset of smoking and nicotine dependence by race/ethnicity in a Midwestern sample of adolescents and young adults from a high risk family study

Objective: The objective of this study was to determine whether race/ethnicity was associated with time to smoking initiation and time from first cigarette to onset of DSM-IV nicotine dependence (ND) after adjusting for familial and individual psychosocial risk factors. Methods: Cox proportional hazards models with time-dependent covariates were used to analyze data from 1376 offspring aged 12-33 years from 532 families at high risk for substance use problems due to paternal alcohol problems and 235 low risk families. Fifty-six percent of the sample self-identified as African-American (AA) and 44% were mainly of European descent. Results: Controlling for covariates, AAs began smoking at older ages (HR = 0.58; 95% CI: 0.48-0.70) and had longer times between smoking initiation and onset of ND compared to non-AAs (HR = 0.25, 95% CI: 0.16-0.39 for ND onset occurring <18 years and HR = 0.49, 95% CI: 0.30-0.80 for ND onsets ≥age 18). After additionally controlling for number of cigarettes smoked daily, the racial/ethnic effects for onset of ND were attenuated, but remained statistically significant for ND onset <18 (HR = 0.34, 95% CI: 0.19-0.61); however, the estimate was no longer significant for later ND onset (HR = 0.84, 95% CI: 0.50-1.41). Conclusions: AA adolescents and young adults initiate smoking at older ages and have longer transition periods between initiation and onset of ND compared to non-AAs, even after controlling for many relevant psychiatric and psychosocial covariates; however, racial/ethnic differences in time to onset of nicotine dependence in late adolescence and young adulthood may be explained by differences in daily quantity smoked.