11 June 2011

Depression and telomeres

Reference: Wolkowitz et al. 2011 March.
People who suffer from major depression have a higher risk of age-related illness and earlier mortality (1 &2). Researchers from University of California, San Francisco (UCSF), investigated (1) telomere length in depressed individuals versus matched controls and assessed other biological factors associated with telomere shortening.

Led by Nobel laureate Elizabeth Blackburn, Ph.D., the team of researchers published their findings in the March issue of PLos One. Their hypothesis was that not all depressed subjects would show shortened telomeres equally because of a large variance in depressive episodes over a lifetime. However, they predicted that those who suffered from depression for long durations would have shorter telomeres due to longer exposure to oxidative stress and inflammation induced by psychological stress.

The scientists recruited 18 subjects diagnosed with Major Depressive Disorder (MDD), excluding those with psychosis or bipolar histories, as well as those with Post-Traumatic Stress Disorder to eliminate confounding variables due to interferences with stress hormone regulation. Results from depressed individuals were compared to those of the matched control group.

Blood samples were taken to measure leukocyte (white blood cell) telomere length, as well as oxidative stress markers (F2-isoprostanes and vitamin C) and inflammation (IL-6). The severity of MDD was determined using the standard Hamilton Depression Rating Scale and total lifetime duration of depression was estimated using a life history method interview. The history-taking and telomere assays were performed blind to each other.

The average age (ranging 36 to 47 years) of the depressed and control subjects in the study didn’t differ significantly, nor did the sex of the subjects, ethnicity distribution, or body mass index. The subjects also did not differ significantly in current or past consumption of alcohol or nicotine, marital status, or highest educational level or socioeconomic status.
The authors reported that, across the broad range of chronic depression types, the “depressed individuals did not significantly differ from controls in leukocyte telomere lengths. However, those individuals with longer courses of major depression had significantly shorter leukocyte telomeres than controls.

Additionally, regardless of depressed status, plasma vitamin C concentrations were significantly correlated with telomere length as was F2-isoprostane levels (a marker of oxidative stress).
“Importantly, the relationship between telomere length and lifetime duration of depression was significant after age was controlled, the authors wrote.

The researchers concluded that, since telomere length is a proposed biomarker of cell aging, their findings could explain why chronically depressed individuals are at higher risk of disease and mortality.

1. Wolkowitz et al. Leukocyte Telomere Length in Major Depression: Correlations with Chronicity, Inflammation and Oxidative Stress - Preliminary Findings. PLos One. 2011 March:6(3):e17837.
2. Brown et al. Association of depression and medical illness: Does cortisol play a role? Biol Psychiatry 55:1-9.

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