Is the relationship between smoking and mental health influenced by other unhealthy lifestyle factors? Results from a 3-year follow-up study among adolescents in Oslo, Norway.

PURPOSE

Several studies have confirmed that smoking is a risk factor for depression in adolescence. These studies have not controlled for other lifestyle factors. The aim of this longitudinal study was to assess the relationship between smoking and depressive symptoms, controlling for other lifestyle factors.

METHODS

This school-based longitudinal self-report survey was conducted among 15- and 18-year-old students in Oslo, Norway. From a baseline cohort of 3811 students, 2489 (65%) participants were followed up after 3 years and completed questionnaires at baseline and follow-up. Mental distress was assessed with Hopkins Symptom Checklist, version 10.

RESULTS

There was a statistically significant association between daily smoking at age 15 and mental distress at age 18 for girls, but not for boys (odds ratio [OR]=2.0 [1.5-2.8] and 1.3 [0.7-2.4], respectively). In girls, the association remained statistically significant even after adjustment for sociodemographic variables and several lifestyle factors. In an analysis of 15-years-old "never smokers," a statistically significant association was found between smoking and mental distress for both genders at age 18. Mentally distressed adolescents at age 15 did not show a higher proportion of smoking at age 18 compared with those not distressed.

CONCLUSIONS

In addition to supporting earlier findings that smoking seems to be causally related to depressive symptoms among adolescent girls, the contribution of this study is that this association only to some extent is confounded by other unhealthy lifestyle habits.