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Is gut bacteria linked to depression? As it turns out, researchers are increasingly finding the profound relationship between gut bacteria and depression, the gut environment, and other mental health symptoms and conditions.
There are a few pathways through which gut bacteria is linked to depression. We discuss it more below, but first, the bacteria in your gut produce and express neurotransmitters. The second way gut bacteria affect depression is because they can reduce inflammation, and inflammation can contribute to depression. Your gut bacteria makeup can also affect your response to stress and cognitive function.
Gut Bacteria and Depression: What’s the Link?
Depression is one of the top causes of disability globally, and according to research, gut microbiota might play a role in depressive symptoms and disorders.
A new study published in Nature Communications found that gut bacteria likely plays a role in depression through the production of neurotransmitters, including glutamate and serotonin.
Depression and its causes aren’t fully understood. Still, multiple factors likely play a role, including genetics, changes to levels of certain neurotransmitters in the brain, environmental factors, and psychological and social factors.
In this newest study, researchers from Oxford Population Health worked with researchers from the Netherlands.
The study, called the Rotterdam Study, looked at data from more than 1,130 participants. The researchers controlled for medication use and lifestyle factors—for example, only people not taking antidepressants were included.
The study found that various identified bacteria are potentially involved in how we produce neurotransmitters, especially those linked to depression, including glutamate.
The research team said they’d found 13 types of bacteria they believe are associated with depression.
Researchers concluded that the bacteria identified are known to be involved in the metabolism of specific molecules, including butyrate and glutamate, and that’s part of how they can influence depression.
The study could have massive clinical implications because the gut microbiome is determined primarily by diet and other lifestyle factors, so it could be that for at least some people treating their depression could include dietary changes and the use of probiotics.
The microbiome produces a range of neurotransmitters, including norepinephrine, serotonin, and nana.
There has been other research that’s looked at what’s called the gut-brain axis. This is a bi-directional communication pathway between the gut microbiota and the central nervous system. When people have dysbiosis and inflammation of the gut, it’s increasingly looking as if these could be linked to mental illnesses, including not only depression but also anxiety.
It’s possible that probiotics can restore balance to the bacteria in the gut and, in the future, might play a mainstream role in treating and preventing anxiety, depression, and other mental health disorders.
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Glutamate in the Brain
A couple of gut species named in the study—Eggerthella and Eubacterium ventriosum produce butyrate. Butyrate is a precursor to GABA, and GABA is a brain chemical that helps control glutamate and regulate it. These species were also found to produce serotonin, and these effects can then influence brain serotonin activity and play a significant role in cognitive, behavioral, and emotional functions.
When glutamate transmission is overactive in the brain, it’s been linked to depression and anxiety disorders.
The gut bacteria linked to controlling brain glutamate activity through regulating GABA and serotonin, particularly through the modulation of the vagus nerve, could represent an important part of maintaining mental health.
The researchers also found that the overgrowth of certain types of gut bacteria can disrupt the gut, the gut-brain axis, and brain chemistry and lead to symptoms of anxiety and depressive disorder.
Can We Change Our Gut Microbiota?
Researchers noted that we could change the composition of gut bacteria with the use of pre-and probiotics. This can come from dietary changes or supplements. For example, you can influence your butyrate-producing bacteria by having a high-fiber diet or trying a butyrate supplement, like sodium butyrate.
The researchers concluded that the study’s most significant takeaway is that the gut microbiome is critical for maintaining our brain functions involved in our mood, thoughts, and behavior.
Which Probiotics Are Best for Depression?
As it stands right now, if you want to improve your gut health to reduce depression symptoms, two strains appear to be most helpful.
The first is Lactobacillus and the second is Bifidobacterium.
Some studies have found positive results on depressive symptoms related to these bacteria strains. Ideally, you might choose a supplement that blends both Lactobacillus and Bifidobacterium, like this one:
I like this probiotic because it includes not only 16 probiotic strains, it’s specifically formulated to support mood and relaxation, and it contains organic ashwagandha.
The Microbiome: More In-Depth
The total of all the bacteria in our gut is known as our microbiome. The microbiome is something we’re learning that can potentially affect, as mentioned above, brain chemistry, emotional behavior, how we respond to stress, and even our perception of pain.
In animal studies, researchers have found that altering the balance between good and harmful bacteria in the gut can change brain chemistry, leading the animal to become either bolder or more anxious.
The brain similarly has a strong influence on gut bacteria. For one example, even a little stress can change the microbial balance in the gut. That could explain why you’re more likely to get sick when experiencing high stress levels—your gut bacteria can protect you less.
Our gut is often called our second brain, the only organ with an independent nervous system, which includes more than 100 million neurons in the gut wall.
When we’re born, our guts are sterile. Then, we develop a unique, diverse set of bacterial species over time.
Our gut bacteria regulate metabolism and digestion and extract vitamins from our food. Your gut bacteria are the programmers of your immune system, they maintain your gut wall, and they can protect you from harmful microbes.
As we discussed above, with the link between gut bacteria and depression, they also produce hundreds of neurochemicals that the brain uses to regulate basic processes and mental processes, including memory and mood. Your gut bacteria manufacture around 95% of your body’s serotonin supply.
In a study with usually timid mice, they were given antibiotics. Their behavior entirely changed—the fearful mice became adventurous and bold.
The treatment with antibiotics also boosted the brain-derived neurotrophic factor or BDNF in the hippocampus.
BDNF is responsible for promoting neural connections and is critical in mood and memory. When the researchers stopped giving the mice antibiotics, they returned to their normal cautious behavior.
Yet another study of mice in 2011 included giving one set of Lactobacillus rhamnosus. The mice in the control group got broth without a probiotic.
The mice in the Lactobacillus group were more willing to go into a maze, which was meant to test anxiety and depression. They were less likely when given a forced swim test and a test intended to be similar to human depression. The mice given the probiotics had reduced physiological responses to the test’s stress, producing fewer stress hormones.
The mice that were given Lactobacillus also had brain regions with an increase in the receptors for GABA. GABA is a neurotransmitter that keeps anxiety under control.
The relationship can go both ways. The brain can influence the gut microbiome, and that can, in turn, lead to behavioral feedback effects. As mentioned above, several studies show that mental stress suppresses good bacteria in the gut. In a 2011 mice study, researchers examined how stress-related gut microbiome changes affected health.
When mice had to share a cage with aggressive mice, a stressor reduced their beneficial bacteria and the diversity of their microbiome. That then allowed harmful bacteria to flourish, making the animals more susceptible to infection and gut inflammation.
Other studies show that inflammatory cytokines can affect the brain’s neurochemistry and make people vulnerable to depression and anxiety. That could be why more than half of people with chronic gastrointestinal conditions like Crohn’s and irritable bowel syndrome also have depression and anxiety.
It’s possible that by keeping anxiety and depression symptoms well-managed and under control, inflammation in the gut could improve. Then, treating inflammation in the gut might change the brain’s biochemistry and enhance mood.
Bacteria and the Vagus Nerve
It appears that bacteria can communicate with the brain through the vagus nerve.
The vagus nerve is one of the primary nerves of the parasympathetic nervous system. The parasympathetic nervous system controls body functions like your immune system, heart rate, and digestion, which are involuntary functions.
The fibers of the vagal nerves send messages between the digestive system, brain and heart, and your vagus nerve runs from your brain to your large intestine.
Final Thoughts—Is Gut Bacteria Linked to Depression?
It appears that, yes, gut bacteria is linked to depression. The newest study reflects some of what we’ve been increasingly learning. Our gut bacteria can make us more likely to develop depression and other mental health disorders, and it’s possible by making changes to improve your gut health, you could see improvements in your mental health too.
Carpenter, Siri, Dr. “That Gut Feeling.” American Psychological Association, September 2012. Accessed January 12, 2023.
Wallace, Caroline J.K., and Milev, Roumen. “The effects of probiotics on depressive symptoms in humans: a systematic review.” Annals of General Psychiatry, February 20, 2017. Accessed January 12, 2023.
Radjabzadeh, Djawad, et al. “Gut microbiome-wide association study of depressive symptoms.” Nature Communications, December 6, 2022. Accessed January 12, 2023.
Clapp, Megan, et al. “Gut microbiota’s effect on mental health: The gut-brain axis.” Clinics and Practice, September 15, 2017. Accessed January 12, 2023.