Yang L, Ruan L-M, Ye H-H, Cui H-B, Mu Q-T, Lou Y-R, Ji Y-X, Li W-Z, Sun D-H, Chen X-B. Depression is associated with lower circulating endothelial progenitor cells and increased inflammatory markers. Objective: To test the hypothesis that depression status in subjects without cardiovascular diseases (CVD) or diabetes is associated with depletion of circulating endothelial progenitor cells (EPCs) and impaired endothelial function. Method: Thirty depressive persons with the first episode of depression (case group) diagnosed according to Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) and 30 healthy people (control group) were investigated. The depression status was estimated using Hamilton Rating Scale of Depression from which the criteria of depression are determined to be >21 score. EPCs labeled with CD34-ECD, CD133-phycoerythrin and kinase insert domain receptor (KDR)-fluorescein isothiocyanate antibodies were counted by flow cytometry in the peripheral blood of patients and control subjects. Mononuclear cells that were positive for CD34/KDR, CD133/KDR and CD34/CD133/KDR within the lymphocyte population were characterised as different phenotypes of EPCs. Results: There were no significant differences in baseline clinical characteristics between patients and healthy individuals (all p > 0.05). However, patients with depression had significantly lower levels of circulating CD34+CD133+KDR+ EPCs (132.20 ± 17.27 vs. 225.93 ± 9.88, p = 0.000) and endothelial colony-forming units (26.40 ± 3.79 vs. 36.60 ± 2.88, p = 0.000) than that of healthy subjects. Furthermore, CD34+CD133+KDR+ EPCs had a negative correlation with tumour necrosis factor-α (Spearman's ρ = 0.433, p = 0.000) and interleukin-6 (Spearman's ρ = 0.441, p = 0.032). Conclusion: Our result shows that depression was associated with lower levels of circulating EPCs, which may contribute to the development of endothelial dysfunction and atherosclerosis.