Since the post about "RePOOPulating the Gut" was so popular I've decided to do a sequel to the role of bacteria in our digestive system. This time focusing on something more complex like the link between the microbiota and depression. It's actually some of the research that my university specializes in and mainly revolves around using mice models.
Over the years, it was observed that some individuals with clinical depression have a dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. What this axis does is it controls the production of hormones in our bodies, specifically in this case corticosterone (CORT) and adrenocorticotrophin (ACTHS) which are both stress hormones.
The link between the microbiota and HPA axis was discovered in 2004 when the response to stress has caused changes in gut microbiota. Specifically, rats underwent neonatal stress when they were separated from their mothers and it was found to cause long-term changes in the diversity and composition of their gut microbiota. Furthermore, when these baby rats were treated with probiotics (Lactobacilllus sp.) their stress hormone levels were normalized during separation from the mothers.
Another way that stress influences the gut bacteria is that it increases intestinal permeability. Due to this event, bacteria can leave the intestines and interact with the adjacent immune cells. Hence, these bacteria can influence the nervous system via reaction with immune system. This phenomena has been observed in rats where pretreating them with probiotics reduced intestine permeability upon stress and prevented HPA hyper-reactivity.
Just as probiotics decrease the stress response, pathogenic bacteria stimulate it. Populating mice with Citrobacter rodentium and Campylobacter jejuni has activated stress circuits through the vagus nerve which has endings in the gut.
So how does this link to depression and anxiety?
There have been experiments designed for mice that can measure anxiety-like behavior. These include putting a mouse in a pool of water and seeing how long it takes before it starts swimming, or putting a mouse in a room with light/dark areas and seeing where does it spend more time. These experiments are actually accurate and the results have been validated in independent laboratories.
One of the main mechanisms of how the gut influences depression is though increased gastrointestinal (GI) inflammation. Mice infected with pathogenic Trichuris muris have shown GI inflammation and anxiety-like behavior. Interestingly, treatment with probiotic Bifidobacterium longum was able to normalize the anxiety-like behavior in these mice.
Some other mechanisms include Brain-derived neurotrophic factor (BDNF), GABA, and the serotonergic system. BDNF is involved with various neuronal processes as well as neuroplasticity and reduction of this factor in the hippocampus is associated with increased anxiety-like behaviors. Not surprisingly, the levels of BDNF can be altered based on the microbiota profile. GABA is a major neurotransmitter and its disfunction has been linked with anxiety and depression. Interestingly, the probiotics Lactobacillus and Bifidobacterium can metabolize glutamate to produce GABA. This has also been observed in mouse models. Lastly, the serotonergic system is one of the main drug targets for mood disorders. In mice it was found that gut composition plays a role in serotonin turnover. Therefore, not only does the gut microbiota influence the brain through inflammation but also through modulation of vital brain molecules.
What about humans?
The effect of probiotics on human health is not well studied but in a double-blind, placebo-controlled, randomised trial it was shown that giving humans probiotics for 30 days has shown significantly decreased psychological distress as measured by various questionnaires.
Do you guys take probiotics? Have you heard anything interesting with regards to the effect of bacteria on human health?
Source: Collins, MS., Bercik, P. (2009) The relationship between intestinal microbiota and the central nervous system in normal gastrointestinal function and disease. Gastroenterology;136(6):2003-2014.
I just started taking a probiotic recently, and can really tell a difference in how my body digests food. I enjoy it. Really interesting information--loved reading through this post. Thank you!!
ReplyDeleteGlad you liked it :) Do you take the probiotics in capsule form or in food? I'm really keen on probiotics and make my own yogurt, oatgurt and sauerkraut.
DeleteI love your Science posts! Very interesting! I'd never heard of a link with probiotics and depression- we are so interconnected! This makes me want to go buy some probiotics!
ReplyDeleteIt's a pretty hot topic right now :) Just get a yogurt starter and make your own home made yogurt because I often doubt that the store bought ones have much thriving bacteria in it.
DeleteGlad you liked the post ;)
Crazy! I'm not a fan of yogurt but since I do deal with depression it would be interesting to see how I feel eating more probiotics...
ReplyDeleteYogurt isn't the only source of probiotics :) There's always kefir or oatgurt :P If not I'm sure you can get probiotics in a capsule form.
DeleteDo give it a try if you wish :) Most of the studies have only been done in mice but were successful. Plus everyone knows probiotics are good why else would we continue using them for thousands of years? So I guess there's no harm in trying :D
Are you sure you're not a Doctor yet? you sound like one for sure:)
ReplyDeleteYou know I really don't ever think of vitamins or pills or how many nutrients, minerals etc. that I need. I truly believe in eating real, whole foods and then feel everything will fall into place.
Hahah thanx!
DeleteThe problem is that your gut microbiota is highly dependent on what you eat and can actually change very quickly based on that. So if you eat fast food and all that jazz it could potentially change the bacteria in your gut. Maybe that's a part of the link between unhealthy food and depression?
I've actually thought about including proBs in my supplement cocktail, so it is good to hear that it might make a big difference, especially during the winter when I feel down a lot.
ReplyDeleteDoesn't hurt to try :) Are you getting enough vitamin D during the winter months?
DeleteThis is really interesting! I always knew that stress affects pretty much every aspect of your body, but I didn't know exactly how/why.
ReplyDeleteI don't currently take any probiotics, but now I'm really starting to consider it. Thanks for the info, Nadiya!
Stress does affect the body in a lot of different ways. Bacterial composition is just one of them :)
DeleteDoesn't hurt to try probiotics, almost all of these studies were done in mice so I'm not sure if it works in humans. Nothing wrong with having some yogurt/kefir/oatgurt/fermented veggies though :D
Love these posts! So much good info.
ReplyDeleteGlad you found it to be useful :)
DeleteA lot of people say that eating yogurt can be good for your health. It helps that someone took the time and went the extra mile to explain its benefits. Now I can enjoy my cup of yogurt more knowing that, by eating this yummy treat, I’m also helping my body. Also, I get to add it to my list of happy food! :)
ReplyDeleteMafalda Cramer
Glad you like yogurt, just be careful with the kind you buy. A lot of commercial packaged ones really don't have much of the live bacteria in them. Personally, I make my own yogurt and it's super easy to find a yogurt starter at whole foods.
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