Feeling Sad? Blame Your Cold

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Whenever I’m sick, I always get down. I feel like I can’t handle normal life, from walking the dog to cooking dinner. I think of myself as “weak.” I have thoughts of being a bad mom because I give my son more screen time.

I’m not alone. Studies show that people cannot accurately identify whether they are getting sick or developing depression early in the course of either condition. We can’t distinguish between the two.

Immune system science

In animals and humans alike, when the immune system gets activated, we feel lethargic, lose our appetite, and withdraw socially. Collectively called “sickness behavior,” these actions help conserve energy so the body can prioritize fighting the pathogen and prevent further spread to members of our kin.

This all makes sense. But why do we have depressive thoughts and feelings? Why do we get cranky or sad?

The culprits are cytokines, inflammatory proteins the immune system produces to signal an attack. Cytokines are like a firehouse alarm. They recruit immune cells (or firefighters) from around the body to help combat the infection or injury. When microglial cells, the immune cells of the brain, hear the cytokine alarm, they activate, causing damage to the surrounding nerve tissue. They reduce neuroplasticity, interfere with the supply of serotonin and other neurotransmitters in synapses, and even produce cell death.

These biological effects can create depressive symptoms. For example, when non-depressed individuals were treated for Hepatitis B with the cytokine Interferon, about a third of the group became clinically depressed. They felt guilty, pessimistic, self-critical, and anhedonic. Other studies show that the people who exhibited the strongest inflammatory cytokine response experienced the greatest deterioration in mood. The bigger the immune response, the worse the mood.

An immune response also makes it harder to do routine things. In a controlled experimental environment, participants who were given Interferon-alpha exhibited increased activation of the anterior cingulate cortex and more task-related errors than the control group. When we’re sick, our brains have to work harder to perform at a normal level.

The next time you get sick, when everything feels harder to do, and you feel down about yourself, remember that it is not in your control. Your immune system is driving the ship. Embrace sickness behaviors. Reduce as much of your daily load as you can, and rest. Let your kids have all the iPad time they want. Be gentle with yourself, knowing that you and your life aren’t the issue. You’re just sick.