Increased Interleukin-6 Levels in Responders with Treatment-Resistant Depression After Bright Light Therapy

Treatment-resistant depression (TRD) remains a challenge despite the growing number of interventions. Peripheral interleukin-6 (IL-6) levels have repeatedly been associated with both the presence and response to different treatments in TRD. There is currently no information available on the effects of bright light therapy (BLT) on serum IL-6 levels. This study assessed the effects of BLT on serum IL-6 levels in TRD patients. Serum IL-6 was determined at two points in TRD patients-at baseline and after 4 weeks of BLT-and at a single point in the healthy controls. Depression severity was measured by the Hamilton Rating Scale for Depression (HAMD)-17 and the Montgomery-Åsberg Depression Rating Scale (MADRS). The study included 104 females, 54 diagnosed with TRD (median age 52.5) and 50 healthy controls (median age 44.5). At baseline, patients had higher IL-6 levels than the controls. BLT treatment reduced HAMD-17 and MADRS scores. Serum IL-6 levels were not significantly affected by the 4 weeks of BLT. However, when patients were divided according to treatment response, IL-6 levels were increased in responders to BLT. The neuroinflammatory mechanism may be involved in the etiopathogenesis and the treatment of TRD, while changes in serum IL-6 levels may be potential indicators of response to treatment.