How calming our immune response can make us happier

Healthy Aging

An exciting path to healthier and happier brains

Our days are getting sunnier and happier! While we’re enjoying every opportunity to activate our vitamin D, this week’s Science Says! shares progress being made on the science front to raise our happiness… interestingly, by getting our immune responses to calm down.

When our immune systems ramp up, our moods go down.

The last time you had a cold or the flu, you likely not only had a runny nose or fever, but probably also experienced fatigue, loss of appetite, lack of concentration, slowness in activity, a bit of sadness, and more.

Hmm… did you know that is the same list of criteria for depression? Well, back in 2000, Yirmiya et al. took note of these similarities, and they did a few interesting studies to test their hypothesis that a ramped up immune response can cause depression.

Okay, I’m in. What did they find?

Yirmiya et al.’s studies had three key findings:

• First, they showed that when humans have immune responses to infections, they develop symptoms of depression. But you have already experienced that yourself.
• Second, they showed that higher proinflammatory cytokine levels were closely correlated with the severity of mood-related symptoms. Cytokines are natural molecules in our body that are the leading instigators of inflammation.
• Third, compounds traditionally used to support healthy moods not only improved mood, they also lowered cytokine levels.

So, that’s pretty interesting.

A surprising evolutionary exploitation of sadness.

Back in our cave days, we likely evolved to have symptoms of depression when infected with pathogens, which forced us to 1) rest and recover, and 2) stay in our caves to avoid being exposed to other things that may kill us when we’re weak. As covered by Anders et al., this use of depression to heal our bodies is called the “infection-defense hypothesis”.

This works great when we only got inflammation from pathogens and broken bones. This work less great when we’re sitting on inflammation all the time.

Calming our immunity really does calm our minds.

Since Yirmiya’s initial studies, numerous clinical trials have shown that compounds which have been traditionally used to calm our immune systems also calm our minds. What?

Indeed, in the 2019 meta-analysis led by Kohler-Forsberg et al., which included 36 randomized clinical trials, they concluded that immune calming compounds (like cytokine inhibitors) can help improve our mood.

A promising frontier for happier days.

Today, we are better understanding how cytokines (especially IL-6 and TNFɑ), which start as high in our bodies, can cross the blood-brain-barrier and activate immune-ramping microglia in our brains. The result? Sadness and anxiety. No, really.

As summarized by Chang et al., it is now well recognized that cytokines contribute not only to chronic, low lying and over-activated immune responses that negatively affect our metabolic, heart, and liver health as we age… this chronic state is also negatively impacting our mood, too.

The new hope? A new frontier of compounds that can calm our immune system, protect our whole body health, and feed our happiness.