The latest research challenges the notion suggested by a growing body of evidence that inflammation and depression are intimately linked. Their findings appear in the journal Psychological Medicine. 

Since the past few years, the idea that inflammation may be what drives and characterizes depression has been gaining more and more ground.

For example, in 2015, found that clinical depression is linked with 30% more inflammation in the brain. A few years later, another study found markers of brain inflammation in people with suicidal ideation, and other researchers have suggested that low-grade inflammation may reduce motivation to perform daily tasks.

Now, a new study by a team led by Eiko Fried, Ph.D., an assistant professor of psychology at Universiteit Leiden, in the Netherlands, applied network analysis to study the links between “individual depressive symptoms, inflammatory markers, and covariates” and challenges this popular notion. 

The Study  

According to the researchers, the existing studies have not yielded unanimous results may be because of two issues: Either the studies have examined different markers of inflammation or specific symptoms of depression may relate to inflammation in differing ways.

The authors applied a method called network psychometrics to examine existing data from the database of the Netherlands Study of Depression and Anxiety. 

This has enabled the researchers to explore shared variances among 

(1) depression severity, modelled via depression sum-score, nine DSM-5 symptoms, or 28 individual depressive symptoms.

(2) inflammatory markers C-reactive protein (CRP), interleukin 6 (IL-6), and tumour necrosis factor α (TNF-α).

(3) before and after adjusting for sex, age, body mass index (BMI), exercise, smoking, alcohol, and chronic diseases.

The database included information from more than 2,300 people, some of whom did not have depression, and some of whom had the condition, with symptoms ranging in extremity among the study cohort.

The Results

The research found no direct link between depression and inflammation, but it has revealed insights into the effects of individual symptoms and lifestyle factors. For instance, “Some specific depression symptoms appear to be related to increased inflammation,” reports Fried, “such as sleep problems.” 

“Overall,” conclude the authors, “the relationship between depression, inflammation, and covariates is likely highly multivariate and multicausal and warrants further investigation.” “This includes the possibility of reverse causation — where depression is not a consequence, but the cause of higher levels of inflammation,” explain the researchers.

For instance, they go on, depression acts as a stressor and may cause unhealthful lifestyle changes such as less exercise and a poor diet, “which may, in turn, increase adiposity and thus inflammatory markers.”

Source: Medical News Today. 

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