Our brains could be collateral damage in our body's fight against infection

You know when you get a cold or flu, how you can feel just out of it?

It turns out that foggy brain feeling we get when we're sick could be due to inflammation. And what's more, even though inflammation — a vital part of our immune system — helps to keep us alive by protecting us from infections, it can also turn on us and our brains. 

Inflammation is how our bodies respond to threats, everything from a bump on the knee, to an infection, pollution or even stress. It activates a cascade of inflammatory molecules that circulate throughout the body to deal with the insult that triggered the response. 

When our bodies have too much inflammation, it can exacerbate illnesses like cardiovascular disease, diabetes, dementia, depression and cancer.

If you actually look at all the studies out there in a host of degenerative disorders, pretty much everything ... has some sort of inflammatory component to it.- Ali Mazaheri, University of Birmingham

But according to many recent scientific studies, inflammation can also affect our ability to think clearly. 

"If you actually look at all the studies out there in a host of degenerative disorders, pretty much everything — whether it be depression, whether it be Alzheimer's, whether it be schizophrenia, it has some sort of inflammatory component to it," said Ali Mazaheri, a Canadian senior lecturer in psychology at the University of Birmingham, in conversation with Quirks & Quarks host Bob McDonald.

This made him wonder what kind of effect inflammation can have on the cognitive functions of healthy individuals. 

Even low-grade inflammation can affect cognition

To test the impact inflammation can have on the brain, Mazaheri injected test subjects with either the salmonella typhoid vaccine, which induces a mild inflammatory response but without any symptoms, or a placebo. 

He measured their brain's electrical activity while they performed attention-related tasks. 

Mazaheri discovered the low-grade inflammatory response only affected one type of attention that relates to how our brains become alert when we need to pay attention to something. 

While he didn't see any difference in their behaviour, instead he found that the brains of those with the mild inflammation — similar to what you'd see in someone with obesity or who's suffering from depression — had to work harder to perform the tasks. 

"Individuals that put in the most neural resources during the alerting aspect [of the attention task], they were also the ones that had the most inflammatory response," said Mazaheri about his findings recently published in the journal NeuroImage. 

He said when we get full-blown cold or flu, we'd likely have 100 times more inflammation than what he studied, and when that happens, the symptoms themselves — the headache and fever — can also affect cognition, making the brain fog even worse. 

Chronic inflammation can lead to serious damage

The real problem with inflammation is when it becomes chronic, meaning that it doesn't go away, which can be caused by everything from autoimmune disorders to obesity, to a host of mental illnesses. 

The more inflammation a person carries, the worse it might be for our brains. 

That is the finding from another study where scientists looked at patients with bipolar disorder, some of whom experience a steeper cognitive decline than others, but the implications could be far reaching. 

When some patients with bipolar disorder experiences a manic or depressive episode, their inflammation levels skyrocket. And the more episodes a person experiences, the more low-grade inflammation they carry when their moods are stable and the more brain damage they might incur. 

What we think we're seeing is an effect of inflammation on cognition in human beings.- Kate Burdick, Harvard Medical School

Kate Burdick, an associate professor of psychology in the Department of Psychiatry at Harvard Medical School and Brigham and Women's Hospital and senior author on the study, said they tested bipolar patients when their mood was stable — and healthy individuals as a control — to see how their cognitive functions are correlated with levels of inflammation.

She found that bipolar patients with higher levels of inflammation were also more cognitively impaired than those without much inflammation. And interestingly, she found the exact same thing with the healthy subjects she tested as a control, but at a lower magnitude. 

"Those individuals who did have elevated inflammation also showed cognitive impairment relative to healthy individuals who did not show that kind of inflammation. So when we reported this, we note that this is not specific to bipolar disorder. Rather what we think we're seeing is an effect of inflammation on cognition in human beings," she said.

Ways to reduce our levels of inflammation

According to Burdick and Mazaheri, the upside of inflammation being a key player in so many illnesses is that we can do something about it.

Medications like Aspirin and ibuprofen reduce inflammation, but Burdick warns this could backfire. A recent study found that when people with depression were given anti-inflammatories, it only worked in those with elevated levels of inflammation.

"But if you give [anti-inflammatories] to individuals who don't have elevated inflammation, it can actually make the depression worse."

Luckily there are many other safe ways we can all reduce our levels of inflammation by following the doctors' orders: eat more healthy foods, get more sleep, reduce stress and of course, exercise.