Associations between inflammation and depressive symptoms in diabetes: A scoping review

Depression is a clinically important comorbidity in people living with diabetes, yet biological pathways linking these conditions remain unclear. Chronic inflammation has been proposed as one mechanism connecting metabolic dysfunction with depressive symptoms. This scoping review examined knowledge on inflammation and depression/depressive symptoms in adults with diabetes, with attention to differences by diabetes type and sex. Thirty-seven studies met inclusion criteria, predominantly observational and focused on type 2 diabetes. Inflammatory markers were more frequently associated with depressive symptoms in type 2 diabetes than in type 1. CRP/hs-CRP was the most commonly studied biomarker and was often positively associated with depressive symptoms, while composite immune-metabolic indices reflected depressive symptom burden across studies. In contrast, findings for individual cytokines, including IL-6 and TNF-α, were heterogenous and appeared dependent on adiposity, metabolic health, or vascular comorbidity. Evidence in type 1 diabetes was less uniform, with studies suggesting involvement of vascular, lipid-associated, or non-classical inflammatory pathways. Sex appeared to modify inflammation and depression associations, although patterns varied across biomarkers and study populations. Overall, the literature suggests that inflammation is relevant to depression in diabetes, particularly in type 2, but that this relationship is heterogeneous and shaped by diabetes type, sex, adiposity, and vascular burden.