Leukocyte mitochondrial DNA (mtDNA) content is associated with depression in old women. 
The purpose of this study was to investigate whether mitochondrial DNA (mtDNA) content of peripheral blood leukocyte is related to depression in community-dwelling old women.  A total of 142 community-dwelling women, older than 60 years, were included in the study.  The mtDNA copy number, which represents the mtDNA content, was measured using real-time PCR methods.  Patients with depression defined as the subjects whose 15-question geriatric depression scale (GDS) score was ≥ 8 or who were taking anti-depressant medication.  We also measured cognitive function, physical performances (gait speed, chair-stand times, tandem standing times) and metabolic parameters.  The depression group had a significantly lower mtDNA copy number than the control group (71.5 vs. 107.3; interquartile range (IQR) = 42.7-116.0 vs. 51.7-202.1; p = 0.028).  The Korean version of the mini mental state examination (K-MMSE) score and physical performance score were significantly lower in the depression group than in the control group (p = 0.041, and p = 0.002, respectively).  After adjustment for confounding factors using multiple logistic regression analysis, mtDNA copy number was significantly related to depression (p = 0.025).  We demonstrated that low leukocyte mtDNA content is related to depression in community dwelling old women.  This finding suggests that mitochondrial dysfunction could be a mechanism of geriatric depression.