Serum interleukin-6 is related to lower cognitive functioning in elderly patients with major depression*

Background: There is an increased evidence of an association between inflammatory mediators, particularly serum IL-6, depression and cognitive impairment in the elderly. This study aims at exploring the relation of peripheral IL-6 to cognitive functions in elderly patients with major depressive disorder (MDD).

Objectives: (1) Assessment of serum IL-6 levels and cognitive functions in elderly patients suffering from major depression and comparing them to healthy age-matched control subjects; (2) correlation between serum IL-6 levels and clinical characteristics of depression and cognitive functions in these patients.

Subjects and methods: The study is an observational, case-control study. It consisted of 80 subjects, 40 with the diagnosis of MDD according to the Diagnostic and Statistical Manual of Mental Disorders (DSM IV-TR) with early onset (first episode before the age of 60) and 40 community-dwelling subjects. They were subjected to the Structured Clinical Interview according to DSM-IV, Montreal Cognitive Assessment, Montgomery Asberg Depression Rating Scale, and serum IL-6 assay using ELISA.

Results: In the depression group, subjects had lower scores in cognitive testing, than the control group (p = 0.001). Serum IL-6 was found to have a negative correlation with cognitive testing in these patients even after controlling for the severity of depressive status and Body Mass Index (BMI) (p = 0.025).

Conclusions: MDD in elderly subjects is associated with decline in cognitive functions that may be related to peripheral IL-6 levels.