Inflammation in the brain maybe a strong contributory factor to depression, according to new research by Dr Daniel Lindqvist from the Psychoimmunology Unit at Lund University in Sweden.
It’s tempting to think there may be an disease underlying some depression in the same way as H. pylori was implicated in stomach ulcers. But it’s wrong to link diseases causing inflammation with depression, Dr Lindqvist told NewsUCanUse.
"Even though many studies points in this direction, a causal relationship between inflammation and depression is yet to be established. Some researchers still argue that inflammatory changes are consequences of depression. In addition, depressive disorders are likely multifactorial and their etiologies are more complex than e.g. stomach ulcers, so even if several lines of evidence suggest an association between neuroinflammation and depression/suicidality there might also be other, non-inflammatory factors in play."
The researchers believe that the cause of the inflammation that sets off the process could vary. It could be serious influenza, or an auto-immune disease such as rheumatism, or a serious allergy that leads to inflammation in the body. A certain genetic vulnerability is probably also required, i.e. certain gene variants that make some people more sensitive than others.
"Studies have also shown that patients with inflammatory disorders such as Multiple Sclerosis and Rheumatoid Arthritis have high risk for depression which is perhaps related to the inflammatory activity of the disease," he told us.
One of the articles in his thesis shows that suicidal patients had unusually high levels of inflammation-related substances (cytokines) in their spinal fluid. The levels were highest in patients who had been diagnosed with major depression or who had made violent suicide attempts, e.g. attempting to hang themselves.
The research group at the Division of Psychiatry in Lund is now getting ready to conduct a treatment study based on its theory. Depressed patients will be treated with anti-inflammatory medication in the hope that their symptoms will be reduced.
Other studies in Daniel Lindqvist’s thesis show that patients with depression and a serious intention of committing suicide had low levels of the stress hormone cortisol in their blood. The cortisol levels were also low in saliva samples from individuals several years after a suicide attempt. This has been interpreted to mean that the depressed patients’ mental suffering led to a sort of ‘breakdown’ in the stress system, resulting in low levels of stress hormones.
"The low cortisol levels sometimes seen in suicide attempters may be the results of a “wear-and-tear” of the stress system due to long lasting and severe psychiatric illness. This is in contrast to patients with acute, melancholic depression who often have high cortisol levels. Therefore it is tempting to hypothesize that chronic depression may cause a burnout of the stress system after long-time high cortisol levels leading to seemingly adaptive changes of the stress system, perhaps going too far, he told NewsUCanUse.
"It is easy to take and analyse blood and saliva samples. Cortisol and inflammation substances could therefore be used as markers for suicide risk and depth of depression", says Daniel Lindqvist.This is a new theory that challenges the prevalent view that depression is only due to a lack of the substances serotonin and noradrenaline.
"However, current serotonin-based medication cures far from all of the patients treated. We believe that inflammation is the first step in the development of depression and that this in turn affects serotonin and noradrenaline", says Daniel Lindqvist.
Source: Lund University and correspondence with Dr Lindqvist
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