Does Inflammation Make Us More Prone to Depression?
By Michelle Robinson

The health of our minds is inextricably linked to the health of our bodies. Now, recent research has shown that maybe this link goes further than we first thought. Much research, sometimes controversial, takes place into the treatment of depression and other mental health conditions. A recent Cambridge University research study on inflammation and depression holds promise for a new direction in treatment.

Does Inflammation Make Us More Prone to Depression?

Inflammation and Depression – The study

Researchers at Cambridge University have discovered a link between inflammation and depression. They found that when inflammation is present in the body, symptoms of depression are more prevalent. The research is still in its early days. However, strong evidence of a causal link between inflammation and depression has already been found.

Studies from 10 years ago have already shown a link between inflammation and schizophrenia. Now the most recent study has added weight to the theory.

What’s the theory?

Some people have higher levels of inflammation in their bodies than others. So offering people anti-inflammatory drugs might be a less drastic alternative than anti-depressants. If you have suffered from the effects of a viral illness before, you will be familiar with the low mood and listlessness that inflammation can cause in the body.

Anti-depressants are a first line treatment for mental health problems, but many people are concerned about side effects. But if, as this research suggests, a physical cause exists for depression, it may be possible to treat it with anti-inflammatory drugs or antibiotics.

So what does inflammation have to do with depression?

Inflammation is the body’s response to illness or injury, and the inflammatory response is triggered by the immune system. Researchers have found that nerve cells in the brain are linked to the functioning of the immune system, and when there’s inflammation present, it has the effect of making people feel low in mood, fatigued, and hopeless; which are some of the most common signs of depression.

The existing research

The Cambridge researchers aren’t the only ones to examine a possible link between inflammation and depression. Research carried out at Aarhus University in Denmark looked at the health records of 3.4 million people. They found that people with inflammatory autoimmune conditions like arthritis or Crohn’s disease were 45% more likely to suffer from a depressive illness. The same study also found that people who had been hospitalised for an inflammatory infection such as sepsis or hepatitis were 62% more likely to suffer from a depressive disorder.

There was another Danish study in the same journal which found that raised levels of an inflammatory marker called C-reactive protein in the body were associated with an increased risk of depressive illness and psychological distress.

A critical question

The results of these studies led to scientists asking the question whether it’s the misery that comes with inflammation and inflammatory illness that causes depression, or is there some unknown process by which inflammation causes depression?

A 2013 Australian study seems to support the latter. It found that giving otherwise healthy people drugs that induced inflammation in the body caused them to develop symptoms associated with depression, like low mood and lack of motivation. To add weight to this theory, ¼ of people who take interferon, a drug that treats hepatitis C, develop major depression. One of the side effects of interferon is inflammation.

The Cambridge study on children

Scientists from Cambridge University studied 4500 children born in Bristol in the 1990’s. They took blood samples to check for the protein interleukin-6, an inflammatory marker the body releases in response to infection. The researchers followed up 9 years later. Children with the highest level of inflammation in their bodies when they were young were twice as likely to develop depression in their teens.

Researchers are looking at what could cause inflammation in childhood, like low birthweight and trauma in early childhood. This could shed some light on why people with high levels of inflammation in childhood go on to develop depression.

Chronic inflammation and depression

Some people have higher levels of inflammation in the body constantly. And the immune system acts as though it is fighting an infection. Where this is the case, people seem to have an increased risk of developing depression.

The Cambridge University team are also researching how chronic inflammation could cause depression. Initial studies on mice suggest the vagus nerve, which connects the brain to the gut, might hold the answer.  Inflammation in the gut causes the vagus nerve to send signals to the brain, telling it to release chemicals like nitric oxide.  These chemicals are bad for brain function, and this could lead to symptoms of depression.

New possibilities for treating depression

The research results open up the possibility that anti-inflammatory drugs like ibuprofen, which cause far fewer side effects that antidepressant drugs, could treat depression. A YouGov poll found that almost 1 in 10 people are taking drugs for anxiety or depression. These commonly cause side effects such as weight gain, fatigue, and cardiovascular issues. Some can even increase the risk of suicide for people in the first few weeks of treatment. Antidepressants known as SSRIs increase levels of the neurotransmitter serotonin, which improves mood and sleep. However, the Cambridge researchers say that SSRI antidepressants may actually help by reducing inflammation in the body.

The researchers hope they might be able to prevent thousands of deaths of people who suffer from depression, by establishing the link between inflammation and depression. People who take antidepressants can die from conditions related to their side effects, such as heart disease, which is also an inflammatory condition. Imagine if we could prevent this by taking something as simple as Ibuprofen?

By revealing drug therapies for depression that are a far cry from anti-depressants, it may not just be mental distress that the Cambridge team helps to alleviate, but physical conditions such as damaged hearts as well.

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