Not to oversimplify since depression can have multiple contributing causes, but there have been many studies published about brain inflammation as an important component of major and minor depression. An illuminating paper published in the latest volume of the journal Biological Psychiatry undertakes an extensive analysis of accumulated scientific evidence. The authors begin by noting:

“Major depression occurs in 4.4% to 20% of the general population. Studies suggest that major depression is accompanied by immune dysregulation and activation of the inflammatory response system (IRS). Our objective was to quantitatively summarize the data on concentrations of specific cytokines in patients diagnosed with a major depressive episode and controls.”

Cytokines are, among other things, signalling molecules that regulate immune system function. This has great practical significance because there is an evidence-based approach in functional medicine to analyzing and treating cytokine imbalances. The authors evaluated 24 studies that included eight different cytokines. Here’s what their data showed:

“This meta-analysis reports significantly higher concentrations of the proinflammatory cytokines TNF-α and IL-6 in depressed subjects compared with control subjects…this meta-analytic result strengthens evidence that depression is accompanied by activation of the IRS.”

You may enjoy the interesting comment on this study just published in Journal Watch.

Although this is a valuable study it’s important to keep a broad perspective. Here’s another paper published not long ago in the journal Pharmacopsychiatry, one among many others on cytokines and depression. It documents cases of brain inflammation with a different cytokine pattern. This paper is also interesting for the therapeutic comparison of Prozac and electroacupuncture:

“An increase in inflammatory response and an imbalance between T-helper (Th) 1 and 2 functions have been implicated in major depression. The aims of the present study were to 1) study the relationship between pro- and anti-inflammatory cytokines and between Th1 and Th2 produced cytokines in depressed patients and 2) evaluate and compare the effect of treatments with electroacupuncture (EA) and fluoxetine on these cytokines.”

Th1 and Th2 are the two primary poles of immune system function, cell-mediated and humoral (antibody). Imbalances result in immune dysregulation. Fluoxetine is Prozac. (The inclusion of electroacupuncture might tip you off that this study was done in Germany.) Their data tells a fascinating story:

“Increased proinflammatory cytokine interleukin (IL)-1β and decreased anti-inflammatory cytokine IL-10 were found in the depressed patients. By contrast, Th1 produced proinflammatory cytokines, tumor necrosis factor (TNF)-α and interferon (IFN)-γ were decreased, and Th2 produced cytokine IL-4 was significantly increased in depressed patients…Both acupuncture and fluoxetine treatments, but not the placebo, reduced IL-1β concentrations in responders. However, only acupuncture attenuated TNF-α concentration and INF-γ/IL-4 ratio towards the control level.”

How interesting that what we call a peripheral sensory nervous system modality (stimulation of the brain through the peripheral sensory nerves, in this case with electroacupuncture) reduced inflammation and TNF-α. This corresponds exactly with my clinical experience employing these modalities for a range of conditions including autoimmune disorders, and explains part of why patients feel so much better after a treatment. Their conclusion is worth noting:

“These results suggest that an imbalance between the pro- and anti-inflammatory cytokines (IL-1 and IL-10), and between Th1 and Th2 cytokines (INF-γ or TNF-α and IL-4) occurred in untreated depressed patients. Both EA and fluoxetine had an anti-inflammatory effect by reducing IL-1β. EA treatment also restored the balance between Th1 and Th2 systems by increasing TNF-α and decreasing IL-4.”

Thus depression involves inflammation, but the cytokine expression can vary.

This topic is multifaceted and a proper synopsis of the functional approach to depression is too long for this forum, but here’s one more paper to keep the horizon open. This study published not long ago in the Journal of Psychiatric Practice investigates the role of low testosterone in depression.

“Studies suggest that testosterone (TT) replacement may have an antidepressant effect in depressed patients…The objective of this study was to explore the effect of TT administration on depression using both a systematic review of the literature and a meta-analysis.”

What did the data show?

“Meta-analysis of the data from these seven studies showed a significant positive effect of TT therapy on…depressed patients when compared with placebo. Subgroup analysis also showed a significant response in the subpopulations with hypogonadism…”

This certainly confirms expectations considering the population of testosterone receptors in the brain and their density in the frontal lobe. Hypogonadism means that the testicles are producing too little testosterone in response to stimulation by luteinizing hormone (LH). This validates my common sense practice of always including biologically active free fraction testosterone and LH in workups for male depression. Note: testosterone replacement, especially by a transdermal route (gel, patch, cream) can give a good initial result but end up back-firing. This is a topic for another post. For now just remember there is a better way.