Leptin in depressive episodes: is there a difference between unipolar and bipolar depression?

Objective: The present study investigated whether peripheral leptin levels are associated with current depressive episodes in a cross-sectional study nested within a population-based study.

Methods: The Mini-International Neuropsychiatric Interview (MINI) 5.0 was used to assess the presence of current depressive episodes. The sample was composed of 206 subjects (103 controls and 103 subjects with a current depressive episode) paired by gender, BMI and age. Medication use and lifestyle characteristics were self-reported.

Results: Serum leptin levels were lower in currently depressive subjects (10.9 ± 12.0 ng/ml) than in the control group (20.3 ± 24.0 ng/ml; p = 0.023). According to the clinical diagnosis, individuals with bipolar depression present lower leptin levels (8.4 ± 8.1 ng/ml) than those with unipolar depression (12.0 ± 13.4 ng/ml) and the control group (20.3 ± 24.0 ng/ml; p = 0.031). In addition, ANCOVA showed that leptin is an independent factor associated with current depressive episodes (p = 0.018).

Conclusion: A decreased leptin level might be a useful peripheral marker associated with depressive episodes in the context of bipolar disorder.