Why You May Feel Depressed And Anxious When You're Ill - And How To Cope With It

20th January 2024

Winter illnesses are all around us at the moment - from the common cold, COVID-19 and flu to strep throat and stomach bugs. All have one thing in common: they can make you feel miserable. These illnesses often come with fatigue, lack of appetite and concentration difficulties. Sufferers often just want to be left alone many people even experience sadness and anxiety.

Researchers have uncovered why that is. When your body is under attack by a pathogen, some of your immune cells recognise the pathogen and take action to eliminate the threat. To be successful, they need to rally other immune cells as well as several organs of your body.

To do so, they secrete specific proteins, called cytokines. These are messengers, communicating the presence of a pathogen throughout your body, including to your brain.

Once the cytokine signal reaches your brain, it triggers changes in the activity of many brain structures. This leads to the development of fever, but not only that.

These brain changes also lead you to feel and act differently: you are much less motivated to do things you usually like and would rather be alone and in bed. Ultimately, you feel fatigued and you lack appetite. But you can also be more sensitive to negative stimuli, which can easily make you sad and anxious.

That means that the psychological experience of sickness is not just triggered by your brain or the pathogen itself - it seems to be unleashed by your own immune system.

Making people sick for one day
How can we make sure that the feelings of sickness are really triggered by our own immune system, and not the pathogen? Researchers have actually shown that such feelings can be brought about without a true pathogen being present.

My research group, and a few others in the world, purposely activate the natural immune defences of healthy and young volunteers, without using a pathogen. In several of our experiments, we injected more than 100 study participants with a small dose of lipopolysaccharide, a component of the membrane of the bacteria Escherichia Coli. Because immune cells recognise this component as a pathogenic threat (although no real bacteria are actually present), they get activated and produce cytokines.

As during a real infection, but without the presence of a pathogen, the cytokine signal reaches the brain and triggers behavioural changes together with the feelings of sickness (collectively called "sickness behaviour").

Interestingly, our participants reported the same symptoms - malaise, fatigue and body pain - without fighting an infection. In the photos below, you can actually see that they look less well after the injection.

That means that the psychological experience of sickness is not just triggered by your brain or the pathogen itself – it seems to be unleashed by your own immune system.

Making people sick for one day
How can we make sure that the feelings of sickness are really triggered by our own immune system, and not the pathogen? Researchers have actually shown that such feelings can be brought about without a true pathogen being present.

My research group, and a few others in the world, purposely activate the natural immune defences of healthy and young volunteers, without using a pathogen. In several of our experiments, we injected more than 100 study participants with a small dose of lipopolysaccharide, a component of the membrane of the bacteria Escherichia Coli. Because immune cells recognise this component as a pathogenic threat (although no real bacteria are actually present), they get activated and produce cytokines.

As during a real infection, but without the presence of a pathogen, the cytokine signal reaches the brain and triggers behavioural changes together with the feelings of sickness (collectively called "sickness behaviour").

Interestingly, our participants reported the same symptoms – malaise, fatigue and body pain – without fighting an infection. In the photos below, you can actually see that they look less well after the injection.

Author
Julie Lasselin
Researcher in Psychoneuroimmunology, Stockholm University
From The Conversation web site