Depression Isn't All in Your Head

The jury’s still out on whether inflammatory diseases cause depression, more and more studies are showing that there is, at the very least, a link between the two. Recently, a study was conducted specifically to take a look at whether the link between inflammation and depression plays out differently between men and women. The findings might be a huge step towards understanding what causes depression in certain focus groups.

In this article, we’ll discuss:

  1. The previous research that has led to this study on inflammation and depression;
  2. how this particular study was carried out;
  3. and the findings.

Previous Research

One of the symptoms of inflammation, called anhedonia, is also recognized as a symptom of depression. While this doesn’t necessarily prove a link between inflammation and depression, it does show a correlation. Anhedonia is defined in the DSM-5 as “a markedly decreased interest or pleasure in almost all activities.” With inflammatory diseases, anhedonia appears more frequently among people who experience higher levels of inflammation.

This decreased interest also shows up in people with depression, usually referred to by people in the field as a lost of positive interest in things that used to bring joy or pleasure, such as going out with friends, walking their dog, or even just eating their favorite foods. Even more important to this study: women are nearly twice as likely to be diagnosed with depression as men are, and of those symptoms they experience most frequently, anhedonia is cited the most often.

A woman with cracks on her skin
Inflammation can make it difficult to get out of bed, which can later lead to depression as well.

The Study

The main goal of the study was to find out if the apparent like between depression and inflammation manifests itself differently among men and women. For the study, researchers induced inflammation in voluntary participants using a substance called endotoxin, which, according to the researchers themselves, “increases inflammation in a safe, time-limited manner.” Another group was given a placebo.

When the inflammation reached its peak, the researchers scanned the patients’ brains with an fMRI machine while introducing them to a game that was designed to grow their anticipation for a cash reward. During the scans, they looked for activity specifically in the “reward-center” of the brain.

The Findings

At the conclusion of the study, the results showed that compared to the placebo group, the women who experienced the greatest amount of inflammation also saw the greatest decrease in brain reward-center activity, meaning the anhedonia was present. These findings were not found among men. 

This is the first study that has shown there is a sex difference in neural response to inflammation--which may account for why women experience depression at a much higher rate than men.

While this study still can’t prove that there is a direct causal link between inflammation and depression, it does further strengthen the link between them. The evidence would suggest that there is, at the very least, a good chance that depression can be influenced by inflammation.

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