“All disease begins in the gut” ~Hippocrates
For the past year, I’ve been doing my senior capstone on the gut-brain axis, and how celiac disease is linked to depression. It was absolutely fascinating to put the pieces of the puzzle together and learn how the two seemingly unrelated conditions could be related. I originally was interested in this topic because in school and at the doctor’s office, I always hear about each body system separately, but never how they all are woven together. I mean, we are composed of all of those systems that make us human organisms, so obviously there is a web of connections between everything that make us, well, us. As a part of my own health journey, this path to more holistic and integrative medicine has been very important. After seeing bunches of doctors who only wanted to treat specific symptoms of what they knew, I was frustrated with the lack of improvement I was seeing. My GI tract has always been a little wonky, and honestly I think that’s the biggest issue in terms of all of my health problems. My research on the gut-brain axis only served to solidify that belief.
The gut-brain axis is a multifaceted connection between the nervous system, which controls the body and internal communication, and the digestive tract, which converts food into energy and eliminates waste. This is a TWO-WAY connection that has 3 big components.
The hypothalamus in the brain controls the pituitary gland, which is in charge of regulating hormone release and endocrine glands. An obvious example of a hormonal gut-brain connection is the release of hunger hormones in response to hunger or satiety. In terms of depression, cortisol and thyroid hormone are super important.
About 70% of the body’s immune tissue is located in the GI tract, which indicates that digestion has a HUGE impact on health. Basically, if your GI tract is screwed up, much of your immune tissue is as well and that’s no fun.
Did you know we have a “second brain?” The digestive tract is innervated by the enteric nervous system, which regulates digestion through direct connection to the brain via the vagus nerve.
Pretty cool, right? Now, you already know from my last post how celiac disease works. As far as depression goes, I focused on three biological markers when doing my research: depletion of monoamine neurotransmitters (such as serotonin), structural brain differences (ie. decreased cortex volume) and hormones (especially cortisol and thyroid hormone).
The biggest common links between celiac disease and depression are brain inflammation and decreased transmission, and there is a variety of ways that these links exist. The constant immune response in the intestines caused by gluten ingestion triggers the overproduction of cytokines, which can travel through the blood, creating systemic inflammation, and through the blood-brain barrier, leading to brain inflammation. Brain inflammation is not good because it decreases nerve conduction and communication. This slows vagus nerve signals, which in turn, further obstructs healing of the GI tract.
This also leads to decreased hormone transmission. Cortisol, the stress hormone, is released in periods of “fight or flight” and normally runs on a negative feedback loop to prevent excess amounts. However, when an individual is chronically stressed (ie. constant acute stress/immune response in GI tract!), this feedback loop is impaired, leading to chronically elevated cortisol levels. Excess cortisol further contributes to inflammation (that immune response just won’t go away), depletion of monoamines and reduction in brain volume (2 depression markers). Inflammation and decreased transmission can also lead to hypothyroid conditions due to decreased energy use and brain activity. This slows digestion, which is why constipation is a common symptom of hypothyroidism. Chronic constipation can also lead to intestinal damage and further inflammation.
As you may remember, villous atrophy is a hallmark characteristic of celiac disease. This damage to the intestinal lining decreases the lining’s surface area, therefore decreasing absorption of nutrients. Decreased absorption of vitamin B6 and the amino acid tryptophan are especially important in the case of celiac disease. Patients with CD have been shown to have high levels of excreted tryptophan. This is a secondary deficiency due a primary deficiency of B6. Tryptophan is converted to serotonin in the body, so if you’re not absorbing enough trp, you’re not producing enough serotonin (which is a marker of depression!). I was surprised to learn that 90% of serotonin is actually in the GI tract and works with melatonin to regulate digestion. Lack of serotonin would slow digestion, leading to irritation and further inflammation.
The microbiome is also an incredibly important aspect of the gut-brain connection. Our GI tracts are full of tons of good bacteria that play an essential role in our health and have a variety of jobs, such as protection from diseases, regulating digestion and processing nutrients. Any disruption of this delicately balanced ecosystem introduces “bad guys” into the gut, which affects immunity and digestion. Dysbiosis is associated with inflammatory bowel diseases, such as celiac disease. A study actually showed that CD patients have more pro-inflammatory bacteria in their guts and that this decreased with the introduction of a gluten-free diet. Pretty cool.
So this is A LOT of information all at once, but the basic takeaway is that everything in our bodies is connected and can affect other systems. This offers an alternative approach to treating some conditions, a thought that isn’t really considered in today’s world of Western medicine when prescriptions are pretty much just handed out for everything. Yes, medication can help and I do believe that there is a time and place for it. However, I also think that there are more holistic ways we can treat ourselves that could be longer lasting, which is the entire reason I created this blog in the first place!
Thanks for reading!
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