Why mental illness is a real disease- and the science behind it

Last month, I wrote an entry comparing mental illness to cancer (http://honyinchiu.blogspot.com/2015/09/what-do-cancer-and-mental-illness-have.html) which led me to start wondering if our immune systems (which helps our body fight against disease and the area in which my graduate study is in) might be involved in mental illness. 

Digging further, I then spent a crazy two days reading scientific research reviews and papers (even in prominent journals like Nature and Cell) and uncovered this whole field of study that has been around for 20 years known as psychoneuroimmunology which studies the interactions between the immune system and the nervous system (our brain, spinal cord, nerves and sensory organs) and how these interactions affect both our mental and physical health. 

I was surprised to find that it's actually been pretty well established for about 20 years that depression is an inflammatory disease. (http://www.sciencedirect.com/science/article/pii/S0278584610002319#bb0720)

Meaning that it is an actual disease that our bodies are physically fighting and not just in our heads. 

As I mentioned before, the immune system is important for our bodies to fight against disease from things like bacteria, toxins, etc and our immune systems become more activated when we're stressed. This is because before human civilization, these stresses usually included things like getting injured by predators, exposure and other physical injuries and so activating our immune system was important to help our bodies protect from infection as well as heal from wounds.

Fast forward to 2015 and now our stresses involve work, relationships, social pressure etc. And from now on, when I say "stress" I'm talking about the mood swings, the overthinking, the negative thoughts, trouble sleeping, etc. Even though the stresses are different from the ones our ancestors had to fight, our bodies are still responding the same way physiologically, which means our immune systems are still being activated even though there is no physical injury. (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4006295/)

OK, our immune systems are more active now, so what? 

Well, increased inflammation is also correlated with a lot of mental illnesses including depression, bi-polar disorder, Alzheimer's, and Schizophrenia just to name a few. There's also evidence that a more active immune system leads to further decline in the mental illness as well as resistance to medications. (http://www.nature.com/tp/journal/v3/n10/full/tp201387a.html)

But why would a higher immune system be correlated with increased mental illness? 

I'm going to switch gears to now talk about this molecule known as tryptophan. Tryptophan is famous for being in turkey and causing sleepiness after Thanksgiving dinner. This is because tryptophan can be made into serotonin (mood, appetite, sleep hormone) and melatonin (which is also a sleep hormone). Both serotonin and melatonin belong to this class of monoamine neurotransmitters (including dopamine) that are thought to control arousal, emotion, and memory. Drugs used to treat depression and other psychiatric patients usually help control the production of these neurotransmitters. 

In the last few years, tryptophan has also been an interesting molecule in the immunology field. The breakdown of tryptophan leads to other molecules that have been found to be important in regulating the immune system.

So there is this theory of tryptophan depletion, where if the immune system is hyper active (from infection or chronic stress), there is a lower pool to be made into the neurotransmitters controlling our moods. (http://link.springer.com/article/10.1007%2Fs11920-014-0541-1)

I should mention that there's obviously a whole lot more than just tryptophan levels connecting our immune and nervous systems (they both secrete other signaling molecules) but I found these particular studies pretty interesting.

And there are other signs supporting this idea as well. I've been told that people who take Ecstasy (which floods your whole body with serotonin and makes you happy) usually have a weakened immune system after. That's probably because tryptophan levels are low from making all that serotonin and there's not enough left to promote their immune systems. 

Or how about how we always seem to get sick RIGHT AFTER finishing finals? I'm thinking it's because our stress levels are high during finals and so our immune systems are more actively fighting against infection. And then once finals are over, we're happy, less stressed, the immune system stops fighting and that's why we get sick.

Of course, these are just based on my non-scientific speculation and I don't think anyone would spend money to run experiments on these urban myths.

So the easy fix is to calm down and stop stressing yourself out? 

Hmm maybe not. I'm not going to go into the details but there seems to be this feed-forward loop of stress inducing inflammation and inflammation inducing more stress. Or it could even start with inflammation inducing stress... think about when we're sick and how cranky and negative we can be even when we don't mean to be.

And if we're not careful they'll just both keep increasing until our bodies are under chronic stress and inflammation and no longer responding to cues that bring it down (I'm talking about glucocorticoid resistance which coincidentally is also involved with cancer, diabetes and autoimmune disease... http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4006295/)

But something's got to give right? Because if they're both just continually being activated with no control, where does that leave us? This is where I believe exercise and meditation are critical to reducing stress, which is something we've known all along. 

Now why am I saying all of this? Does this mean we have no control over our minds?

No, my point is that our bodies and minds are connected in more ways than we're capable of comprehending and there's also genetic and environmental factors that I haven't even covered. I also believe this further shows why we need to treat mental illness with the same care and understanding as we treat those with physical illness because hopefully I've shown you some evidence that YES, mental illness is a real disease.

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I know some of the links I posted are to articles with only the abstract but if you want a copy of the full paper you can contact me and I can send it to you (they're free for me).

I also have A LOT more papers than the ones I included in this entry if anyone wants to read more...