In the fully adjusted model 2 including group, age, gender, HRSD-17 (total score), YMRS (total score), alcohol consumption and smoking status, patients with bipolar disorder had a statistically significant higher BDNF level of 22.5% compared with healthy controls (B = 1.225, 95% CI 1.067–1.406, P = 0.004, Table 2). Here, BDNF is linked to bipolar disorder.