For the analysis, data from 173,890 individuals aged 19 to 72 were evaluated, with women comprising 50 percent of the sample. Participants provided information via interviews and standardized questionnaires regarding physician-diagnosed depression, current depressive symptoms, and smoking behavior. Participants were categorized into three groups: 81,775 had never smoked, 58,004 were former smokers, and 34,111 were current smokers.
“Although the association between smoking and depression is well-established, the mechanisms underlying this interplay remain insufficiently understood. In our study, we therefore focused in particular on dose–response relationships and temporal factors, such as age at smoking initiation and duration since cessation,” explains Maja Völker, doctoral candidate in the Department of Genetic Epidemiology in Psychiatry at the CIMH.
Clear Dose–Response Relationship Demonstrated
The results reveal distinct dose-dependent effects: the greater the number of cigarettes smoked per day, the more pronounced were current depressive symptoms (0.05 additional symptoms per additional cigarette). Age at smoking initiation also played a role: a later onset of smoking was associated with a later emergence of the first depressive episode (0.24 years per year of delayed smoking initiation).
Differences between smokers and never-smokers were most pronounced in the 40–59 age group. “This suggests that, in addition to social factors, temporal effects may also influence the relationship between smoking and mental health,” notes Carolin Marie Callies, doctoral candidate at the Chair of Health Psychology at the University of Mannheim.
Smoking Cessation Benefits Mental Health
A central finding of the study is that the longer the period since smoking cessation, the longer the interval since the last depressive episode (0.17 years per year of abstinence). “Our observations underscore the importance of preventing smoking initiation and promoting cessation to improve mental health. Particularly noteworthy are the dose-dependent effects of smoking behavior: higher cigarette consumption was associated with more severe depressive symptoms, whereas longer periods of abstinence correlated with improved depression outcomes,” emphasizes Dr. Fabian Streit, DZPG researcher at the Hector Institute for Artificial Intelligence in Psychiatry at the CIMH.
Outlook: Further Research Planned
The researchers note that the cross-sectional design of the study does not permit causal conclusions. Future longitudinal analyses, as well as the integration of genetic and neuroimaging data, are intended to advance the understanding of underlying mechanisms and potential causal relationships.
Source: Press release of the Central Institute of Mental Health (CIMH)
