Association between insulin resistance and serum insulin-like growth factor 1 levels in patients with non-remitting major depressive disorder

Background: Major depressive disorder (MDD) is linked to an increased risk of diabetes; however, the underlying pathomechanism remains unknown. Although insulin-like growth factor 1 (IGF-1) is involved in the pathogenesis of both insulin resistance (IR) and MDD, no studies have investigated the relationship between IGF-1 and IR in patients with MDD. Methods: We recruited 120 patients with MDD (84 non-remitting patients and 36 remitting patients) and 99 control participants. Blood samples were collected after overnight fasting to investigate associations between serum and clinical factors, such as serum IGF-1 levels and homeostasis model assessment-insulin resistance (HOMA-IR). Results: Serum IGF-1 levels were higher in patients with non-remitting MDD than in control participants and patients with remitting MDD (P = 0.001 and P = 0.007, respectively). There were no significant differences in HOMA-IR between the three groups. HOMA-IR was positively correlated with serum IGF-1 levels in patients with non-remitting MDD (R = 0.355; P= 0.001) but not in control participants or patients with remitting MDD. A stepwise multiple regression analysis with various clinical factors revealed a positive association of serum IGF-1 levels and body mass index with HOMA-IR in patients with non-remitting MDD. Limitations: This is a cross-sectional study and therefore we cannot draw firm conclusions about causal associations. Conclusions: Serum IGF-1 levels may play a role in IR in patients with MDD who fail to achieve remission. Further studies, including longitudinal studies, are needed to determine the relationship between high serum IGF-1 levels and subsequent IR and diabetes risk.