A combined analysis of worldwide studies demonstrates an association between bipolar disorder and tobacco smoking behaviors in adults

Objectives: Worldwide studies were combined to examine two hypotheses: (i) bipolar disorder is associated with smoking behaviors, compared with the general population; and (ii) smoking behavior prevalences in bipolar disorder are intermediate between those in major depressive disorder and those in schizophrenia. Methods: Combined analyses used 56 articles on adults obtained from a PubMed search or the senior author's article collection. Odds ratios (ORs) and their 95% confidence intervals (CIs) compared current smoking, heavy smoking among current smokers, smoking cessation in ever smokers, and ever smoking in bipolar disorder versus control groups. Results: The combined OR was 3.5 (CI: 3.39-3.54) in 51 current smoking studies of bipolar disorder versus the general population from 16 countries. More limited data provided an OR = 0.34 (CI: 0.31-0.37) for smoking cessation and an OR = 3.6 (CI: 3.30-3.80) for ever smoking. The combined OR was 0.76 (CI: 0.74-0.79) for current smoking in bipolar disorder versus schizophrenia in 20 studies from ten countries. Ever smoking may be lower in bipolar disorder than in schizophrenia (OR = 0.83, CI: 0.75-0.91). The OR was 2.05 (CI: 2.00-2.10) for current smoking in bipolar disorder versus major depression in 18 studies from seven countries. Ever smoking may be higher (OR = 1.5, CI: 1.40-1.70) and smoking cessation lower (OR = 0.51, CI: 0.45-0.59) in bipolar disorder than in major depression. Conclusions: Increased current smoking in bipolar disorder versus the general population reflected increased ever smoking (initiation) and decreased smoking cessation. Smoking behavior frequencies in bipolar disorder may be between those in depressive disorder and schizophrenia, with schizophrenia showing the highest severity level.