Saturday, October 27, 2012

What is Evolutionary Psychiatry?

I am in the midst of a new academic year of talks. Last week I went to the Brigham and Women's Hospital behavioral neurology interest group talk, and last Thursday to Boston University Medical Center Psychiatry Grand Rounds.  I do like these academic talks, though naturally the audience is much more skeptical than the Ancestral Health Symposium and PaleoFx folks. Skepticism is good. Keeps me on my toes. At the Brigham Behavioral Neurology group, I had immediate questions involving how long our ancestors lived, how old was the individual who owned the beautiful choppers in the ancient Maori skull when he/she died, and what exactly were the questions asked by Staffan Lindeberg and company to determine that the Kitavan elders didn't seem to have symptoms of dementia.

All important questions! I didn't have answers to as many as I wanted to… but I think I held my own. I do try to make the point that my blog is not about answers, but rather about asking these questions for research in a meaningful way. If the government food plate leads us to "whole grain" sugary honey nut "O" cereal as a big healthy part of our diet, and beautiful nutrient-rich egg yolks are deadly, maybe we should step back and think about that for a moment.

Grand Rounds at Boston Medical Center went well. I thought the talk was received with interest, and I certainly thank Dr. Searl and Dr. Chapman for inviting me to speak. I hope that someone thinks about a research idea…I'm particularly hopeful that we will get more research about fructose malabsorption and depression. We'll see.

Recently I've been hard at work reading an amazing textbook about the immune system and evolution recommended to me by Kurt Harris.

The textbook has quite a bit to say about mental illness, a whole chapter (pages 189-220), which is quite amazing, as most anthropology and hygiene hypothesis tends to avoid mental illness. So much easier to focus on diabetes and obesity and autoimmune disease. All easily marked and tallied. Not so mental illness, defined by the recipe book of symptoms we call the DSMIVTR.

Well. Stress-related psychiatric disorders (which is nearly all of them, when I think about it), particularly depressive and anxiety disorders, are associated with markers of inflammation, particularly raised levels of proinflammatory cytokines.  Some of the proinflammatory cytokines (most famously interferon alpha, used to treat hepatitis C) can induce depression in folks with no previous symptoms. Thus it is reasonable to assume that immune dysregulation, that is our immune system a bit out of whack, like an army milling about without clear leadership, could be part of mental illness.

Like autoimmune disease and allergic disorders (athma, hay fever, type I diabetes, multiple sclerosis, and inflammatory bowel diseases such as ulcerative colitis) have been increasing preciptiously in the developed world in recent decades. The "old friends hypothesis" suggests that we are, in effect, missing a major regulator of our immune system that we co-evolved with for thousands upon thousands of generations. That is, three classes of organisms who have lived within us or passed through us, all of our ancestors, until very recently. They are the pseudocommensals, the commensals, and the parasitic worms. (More about the old friends hypothesis in this article.)

The down and dirty of it is that we have several arms of our immune system, kind of like infantry and navy and military intelligence. There are various forms of T helper cells (Th1 and Th2) that secrete inflammatory cytokines to tell which arms of our immune system to come forth and attack.  What will tell the Th1 and Th2 cells to back off is a third variety of T cell, called Tregs (short for regulatory T cells). Infection with our "old friends" (such as pinworms, or tapeworms, or the pseudocommensals like soil mycobacteria) seems to cause continuous activation of the Tregs, keeping the Th1 and Th2 cells in check. In effect, these "old friends" organisms have always been there, and have become a part of our immune system. It is no wonder that we have problems when we no longer have the old friends at our disposal.*

Both Th1 and Th2-regulated inflammation have been associated with anxiety and depression. The "pro-inflammatory cytokines" IL-1, IL-2, IL-6, IL-12, TNFalpha, and interferon alpha and gamma. On the Th1 side, IL-6 and IL-1 levels are related to symptoms of depression in cancer patients and others. Downstream agents, such as C reactive protein, cerulosplasmin, and lower levels of zinc and albumin are also associated with depression symptoms. There are also increased levels of neutrophils and complement proteins** seen in acute exacerbations of bipolar disorder and major depressive disorder. Seems that people with increased levels of background inflammation are more susceptible to interferon and IL-2 administration causing depressive symptoms as well.

When we go over to the Th2 side of things (Th2 excess seems to be associated with allergies and hay fever and ulcerative colitis, whereas Th1 excess is associated with other autoimmune diseases such as type I diabetes and crohns), the evidence for specific cytokines is not as clear. However, people with allergies are known to have a greater incidence of depression. 50% of asthma sufferers seem to have clinically significant depression, and allergies are associated with an increased risk of suicide.  Asthma is also clearly associated with anxiety (in studies, and also any experienced clinician can tell you… trouble breathing causes great anxiety and worries about future attacks). However, that association begs an important question…is it the immune dysregulation causing both anxiety and asthma, or the asthma symptoms particularly prone to causing anxiety? Until we have a better handle on the Th2 cytokines such as Il-4 (experimental tests are problematic) we may not know.

So, there is an enzyme called IDO, which can act on tryptophan leading to a depletion of serotonin. Inflammation seems to activate IDO, whereas antidepressants (such as SSRIs) seem to deactivate it, which may be the secret to how they might work. In pregnancy, there is a bias toward Th2 and regulatory T cells (thought to prevent immune attack on the growing fetus. Mothers-to-be are in a somewhat immune compromised state, particularly in the third trimester, which can actually decrease the incidence of some autoimmune symptoms during pregnancy). After pregnancy, however, there seem to be a Th1 "bounce back" that can lead to exacerbation of inflammatory disorders and depression. There is increased metabolism of tryptophan and increases in Th1-related cytokines.

The Dead Weather: I Can't Hear You (starts with an ad that can be skipped after a few seconds) 

What about the gut and depression? Are raised levels of immune cytokines seen in depression caused by "leaky gut"? Levels of antibodies directed against several gut bacterial species are elevated in people with depression, suggesting leakiness. Leakiness is associated with increased bacterial endotoxin crossing the gut barrier, leading to increases in proinflammatory cytokines, which could plausibly cause depression symptoms. Gut epithelial barrier permeability is highly dependent upon the enteric immune system, and parasites and healthy, normal commensal organisms may help regulate and protect normal gut integrity. It's not a coincidence that Chron's and ulcerative colitis are associated with higher levels of affective disorders. 

Depression is also very common in folks with vascular disease (those at high risk for heart attacks and thrombotic strokes). Metabolic syndrome, associated with athersclerosis and heart disease, is also associated with depressive symptoms. Brain-derived neurotrophic factor (a nerve fertilizer of sorts) seems to be diminished in depression and in vascular disease. Levels of BDNF are low before treatment, and seem to rise in response to succesful treatment. Autoimmune diseases such as MS are also noted for low levels of BDNF. 

There are a lot of intriguing connections between whole-body immune pathology and depression and anxiety symptoms. Gut and immune dysregulation may be keys to these disorders. It will take more time and more asking the correct questions to find out whether these issues are of fundamental importance or not. Psychiatrists might want to read up on the immune system, however, as a part of continuing medical education.

*there are clear benefits to a hygenic water supply (unless you like cholera for breakfast), not eating dirt, and not having unchecked parasitic infections. Don't go drink untreated pondwater after reading this post. But my guess is that better study of these organisms will lead to safe and ingenious ways to emulate the old friends with much less risk than drinking untreated water and living with hookworms.

** a thorough grounding in immunology is beyond the scope of my post. However, these wikepedia articles can give you a good start.


  1. Keep it up, Emily! I love you so very much!

  2. Great!!

    Do you think this is more or less correct? Dysbiosis causes inflammation in the gut which activates IDO. IDO will stimulate the production of kynurenine which implies less serotonin and tryptophan and more 3-OH-KYN (which damages neurons) and quinolinic acid (an excitotoxin).

    1. Yeah, that's pretty much my take, though I'm not willing to say it is the only cause of depression or serotonin depletion… stress on it's own could probably do it. Certain hormones, etc.

  3. Nicotinamide inhibits IDO (because a purpose of IDO is to supply NAD+ for some reason, sirtuins maybe, respiratory burst, or to sequester it from pathogens - like iron - or all 3 plus adaptive depression).

    Reading "An Epidemic of Absence" was an illumination - I've looked at this stuff for ages in a narrow way (commensals and inflammation) but the possibilities are staggering.

    I have a well in my back yard fed from mountain streams; no human or livestock contamination, but plenty of saprophytes and algae. I've drunk from it off and on for years, but I decided to drink 2x a day or more every day and avoid bottled or tap water and pay attention to see if it helped my hay fever.

    In a word, yes, it seems to work; I've sneezed 5 or 6 times in 3 weeks; no uncontrolled fits, very little irritation of nose or eyes. We'll see if it lasts, but if it does, that will be amazing.

    1. There's a whole chapter in the Rook textbook about skin commensals, NO, and how bathing and shaving, etc. could reduce the amount of nitrates we get. My family has a farm in North Carolina where we drink spring water, obtained from a protected area so the cows don't mess with it… saprophytes, mycobacteria, eukariotic organism (like the helminths) all have a huge impact. The research is really just beginning, but it would be nice to be able to add back that piece of our immune system we are missing in a safe and effective way.

    2. Would you recommend An Epidemic of Absence as a solid text?


    3. I've heard it is a good book, though a little sensationalist.

  4. It looks like timing is critical if microbiota are to prevent allergic/autoimmune disease; adding them later, not so reliable (probiotics have increased asthma in children in one trial).
    It seems to me the inverse of the diet conundrum; VLC diets mitigate DM2 but not so easy to prove that high-carb diet causes it;
    absence of microbiota leads to autoimmunity but not easy to prove that replacement will cure it (yet).

    It is possible to supply TLR-active PAMPs without living organisms. I am thinking a broad-spectrum approach across all the TLRs; extracts of representative species of all relevant organisms, including insects.
    One day we might dose our kids with extracts from pinworm, fleas and headlice.

    1. Yes, in general experiments such as deworming pregnant mothers etc. have resulted in increased allergies and excema in the children, but sometimes exposure to worms have increased the allergic response. The subtleties are currently beyond us. And of course 50,000 kids a year die in Africa from hookworms, there are advantages to hygiene! It's all about the details, which we are only beginning to figure out.

  5. How about adrenals and cortisol?

    I've just been bitchslapped back to the living with 5mg prednisone. Pain relief when absolutely nothing else worked. (Will reduce dose to see if less works.) All I can say is 'Wow!'

  6. Fascinating. Funny, I had an itch to hear that exact Dead Weather song last night, too!

  7. I deleted this comment by accident while trying to accept it (sorry!)

    Theresa Davies has left a new comment on your post "What is Evolutionary Psychiatry?":

    Hi Dr Deans, I am a core trainee in Psychiatry in the UK in my second year (of 6). I was so excited to find your blog as I have been trying to motivate my collegues to think of dietary factors when diagnosing patients (without much success!!). I have to do a journal club presentation and I wondered if you had a randomized controlled trial I could present to get them thinking? Thanks for your help, Dr Theresa Davies

    1. Hi Dr. Davies,

      Honestly the best evidence is for ADHD. Lovely crossover INCA trial and then the Southampton studies… I covered them (and linked the studies) here:

      And also there was a decent review later on I linked here:

      And the other really nice avenues of research have been the diet and violence studies:

      And finally, the avenue that has been poorly researched but has so much potential is fructose malabsorption:

      Hope that helps!!

  8. I understand your advice not to go out and drink dirty water, obviously, but how about smelling forest soil for help with depression? I don't think those mycobacteria are associated with human disease, right? (I do understand that other species cause TB).

    I teach nature and gardening classes to kids, and I often wonder if one of the many positive effects of outdoor play might be the smell of the soil.
    I enjoy the smell of soil myself and wonder if it has positive effects. It could also be that the smell is connected in my mind with pleasant memories.

    Dietary selenium and major depression: a nested case-control study.
    After adjusting for age and SES, compared with a high selenium intake, a low intake (<8.9 μg/MJ/day) was associated with an approximate trebling of the likelihood for developing de novo MDD; OR 2.95 (95%CI 1.00-8.72). Smoking, alcohol consumption and physical activity did not confound the association.

  10. Oops, that first line of my post came out sounding flippant and I didn't mean that at all. I just wanted to ask what you thought about smelling the soil.

    I love your blog.


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