Depression in type 2 diabetes: A systematic review and meta-analysis of blood inflammatory markers

The prevalence of depression is higher among people with type 2 diabetes (T2DM). Individually, both conditions are associated with systemic inflammation. This study aimed to summarize the clinical data comparing peripheral inflammatory markers in blood between people with T2DM, with and without comorbid depression. From 2187 records, we identified 20 original peer-reviewed articles from which blood inflammatory marker concentrations could be combined and compared between people with T2DM and comorbid depression (D) vs. no depression (ND) as standardized mean differences (SMD) in random effects meta-analysis. Concentrations of C-reactive protein (CRP; N_D/N_ND = 1742/15244, SMD = 0.31 95% confidence interval [0.16, 0.45], Z₁₆ = 4.03, p < 0.01; I² = 84.0%) and interleukin-6 (IL-6; N_D/N_ND = 677/4349, SMD = 0.17 [0.04, 0.30], Z₄ = 2.58, p = 0.01; I² = 48.1%), were higher, and concentrations of brain derived neurotrophic factor (BDNF; N_D/N_ND = 358/1512, SMD = -0.37 95% confidence interval [-0.64,-0.10], Z₂ = -2.68, p = 0.01; I² = 61.2%) were lower, among those with depression. Depression in T2DM was associated with systemic inflammation and lower peripheral blood BDNF concentrations. Inconsistency between studies suggests the need to explore further population heterogeneity and pathophysiological elements. PROSPERO (CRD42020188509).