Several studies have described the link between depression and inflammation , since many patients diagnosed with an inflammatory disease show depressive symptoms.

Not that there is any argument that having an inflammation will always lead to depression, but it has been found that both conditions have a high comorbidity, suggesting that they have a biological link in common

Next we will talk about the theory that tries to explain this phenomenon, as well as going deeper into the biological causes behind this process.

The link between depression and inflammation

It has been seen that patients diagnosed with major depression are more likely to have inflammatory processes. In turn, people who suffer from chronic diseases, in which a high immune response is produced , are more likely to be diagnosed with a mood disorder.

Among the diseases in which inflammatory processes are present and in which we have been able to see the greatest relationship with depression we have, to say the least, diabetes, rheumatoid arthritis, asthma, multiple sclerosis, cardiovascular problems, chronic pain and psoriasis.

Next we will see the main theory that has tried to establish and explain the relationship between both health problems.

Flaming Brain Theory

This theory has been proposed to explain the relationship between depression, a mental disorder, and inflammation, a physiological process .

Several studies have noted that people who are diagnosed with major depression have higher levels of a factor that is involved in inflammatory processes, cytokines.

It seems that cytokines can alter the brain at a functional and structural level , thus inducing changes in both mood and cognitive abilities.

It has been pointed out that inflammatory processes in Western societies would be related to an unhealthy lifestyle, especially in relation to two factors: diet and environmental pollution.

Others, however, argue that the cause could be internal, caused by our way of reacting to environmental stressors, along with a style of thinking that induces worry in an unadaptive way, manifesting itself in physiological symptoms such as inflammation.

In other words, we are so stressed and depressed that our body reacts physiologically, and that causes immune diseases to occur.

Stressful situations cause the body to release the stress hormone, cortisol . In turn, this hormone causes increased levels of cytokines in the blood, and substances that are associated with wear and tear at the cellular level, such as nitric oxide.

Mechanisms that would be behind this link

The organism, being healthy, reacts to external pathogens through immunological processes. In this way, it activates the cells in charge of defending the human body, preventing pathogens, whether they are viruses, bacteria or parasites, from spreading freely and reaching their goal: to make us sick.

However, the immune process itself involves some temporary wear and tear and discomfort as the body tries to cope with the external threat.

The inflammatory process is that response against the threat, and implies some temporary discomfort , such as when you have a fever or inflammation in a part of your body.

The hypothesis behind the idea of the burning brain is that social pressures, insecurities and any psychological problems can induce this same inflammatory response, as if they were viruses.

The problem with social pressures is that they are difficult to solve or lessen and, if the person faces them in an unadaptive way, he or she subjects his or her brain to constant stress. This causes psychopathology and organic problems to manifest themselves.

Depression and inflammatory biomarkers

Cytokines are proteins that are released during the inflammatory process, and serve to activate the immune system, stimulating it to cope with external threats .

As we have already seen, one of the inflammatory biomarkers, cytokines, show up in greater quantities in people who are experiencing depression, which could be the biological link between inflammatory processes and mental health.

Cytokines and cognitive problems

Patients who have depression have been shown to have, on average, greater cognitive problems compared to people without the diagnosis.

Problems become especially important in areas such as attention, executive functions, memory, in addition to showing other cognitive deficits .

It has been seen that these problems correlate positively with having higher levels of cytokines and also with the presence of other factors involved in the inflammatory process.

It appears that cytokines and other immunological factors may play a central role in synaptic plasticity and other cellular mechanisms involved in cognition.

This relationship between inflammation at the neurological level and cognitive dysfunctions has its evidence, especially if we take into account a disease such as Parkinson’s, Alzheimer’s or mild cognitive impairment.

It is quite well known how beta-amyloid plaques, which are present in several dementias, affect function at the cognitive level and also involve, along with cytokines, inflammatory processes.

Thus, neuroinflammatory processes appear to lead to changes at the cognitive and behavioural level through various mechanisms, including changes in gene expression, and neuronal functioning.

Depression in patients with inflammatory diseases

Inflammation takes on a very important role in various metabolic, neurological and behavioural conditions . Not surprisingly, it has been associated with depression. Below we will look at several medical problems in which this immunological process takes place and which can be related to depression

Depression in people with diabetes

It has been known for a long time that there is a relationship between depression and diabetes.

There is a high prevalence of people with insulin problems who manifest symptoms of depression ; but, since both depression and diabetes are very common conditions, some comorbidity is to be expected.

However, epidemiological studies have shown that the two diseases too often occur together, which has suggested a relationship between sugar levels and depressive symptomatology .

It should be noted that although well-treated diabetes is not fatal, it is a chronic condition, which would cause the newly diagnosed person to experience depression for a while.

What we have seen is that having high blood sugar levels is statistically associated with low mood .

In addition, the lifestyle of many depressed people and diabetics coincide. It is frequent that in both diagnoses, the profile of the person is that of someone who eats food rich in sugars and fats, in addition to being sedentary.

Depression, Rheumatoid Arthritis and Multiple Sclerosis

Depression seems to occur 5 to 10 times more often in people with a serious medical problem , such as arthritis or sclerosis type diseases, where the person becomes progressively weaker.

It has been seen that about half of the people who suffer from multiple sclerosis, either by a biological inflammation-depression mechanism or by being aware that their disease is chronic and neurodegenerative, are diagnosed with major depression.

In other diseases, also of an inflammatory type, such as rheumatoid arthritis, psoriasis and gastrointestinal diseases such as Crohn’s disease, the ratios are between 13 and 17% of cases with depression.

Conclusions

On the basis of the literature consulted, it appears that the link between depression and inflammation is solid , being seen in multiple medical conditions in which there is affectation at the immunological, metabolic, behavioural and cognitive levels.

Depression occurs in a higher percentage of people who have been diagnosed with an illness that has endocrine involvement, such as diabetes, inflammatory diseases such as arthritis, sclerosis and gastrointestinal problems.

In any case, despite the relationship between the two problems, it is understandable that one will not necessarily generate the other. The reason why a person with a chronic illness has been diagnosed with depression may be because, after receiving the diagnosis of their medical problem, they became depressed because of it, not as a symptom of the medical illness.

Bibliographic references:

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