Depression is a common and sometimes debilitating mental health condition. It can affect anyone at any age, but this mental health condition becomes more common later in life.
It’s not clear what causes depression and the complexity of the brain doesn’t make it any easier to determine its underlying cause. No wonder! The brain is a multifaceted mysterious organ that researchers don’t fully understand, but they’re continuing to catch glimpses of what makes the brain work the way it does.
Although depression causes changes in certain key chemicals in the brain called neurotransmitters, a growing number of experts believe depression may begin in an area removed from the brain, the gut.
The Gut and Depression
The brain and the gut have more in common than you think.
It surprises people to learn that the human gut produces some same neurotransmitters that the brain does, including ones that affect mood.
Notable examples are serotonin and dopamine. In fact, some researchers refer to the gut as the “second brain.” This second brain comprises over 100 million neurons or nerve cells. That’s how intertwined the gut and brain are.
In fact, the relationship between the gut and the brain works bi-directionally with signals traveling both ways. When you feel anxious or sad, you might experience nausea or diarrhea or when you’re frightened you get a knot in your stomach.
That’s your brain communicating with your gut.
But how does the gut communicate with your brain?
One way is through the nerve connections that link the brain and the gut together, particularly the vagus nerve. However, bacteria living in your gut also communicate indirectly with your brain.
They have more influence than you might think, and it all starts with the microbiome.
The Role of the Microbiome in Depression
The bacteria that make up your gut are referred to as the gut microbiome. This internal ecosystem is teaming with trillions of bacteria, many of which perform useful functions.
For example, gut bacteria aid in nutrient absorption, fight off “bad” bacteria that could cause illness, and even influence immune health. However, these bacteria also produce chemicals that can enter the bloodstream and travel to the brain where they may influence mood and brain function.
Most of the evidence that gut bacteria impact mood is in rodents. Research shows that bacteria in the gut influence how mice respond to stress and how easily they learn and remember.
Based on these findings, scientists are optimistic about the potential for “psychobiotics” to positively impact brain health and mental health. Psychobiotics are living bacteria that influence brain activity.
You’ve heard of probiotics, living bacteria beneficial to the gut. However, psychobiotics are bacteria that specifically impact mental health.
The idea behind psychobiotics is that supplying the gut with certain bacteria is beneficial for the brain and for mood. When you consume friendly bacteria, they populate the supportive lining of the gut.
Once they settle in, they produce factors that impact brain activity and mood. In mice, psychobiotics boost brain-derived neurotrophic factor (BDNF), a hormone-like substance that enhances learning and memory.
Researchers discovered that people with major depression have lower levels of BDNF.
In terms of depression, some studies show that people who are depressed have lower levels of Lactobacillus and Bifidobacterium, two gut-friendly strains of bacteria. Although we can’t say that reduced levels of these bacteria cause depression, it’s an intriguing association.
The goal of psychobiotics is to replenish these and other bacteria that might be beneficial to the brain and mental health in the same way that people take probiotics. The hope is that the bacteria in psychobiotics will rebalance key neurotransmitters that impact mood such as serotonin, GABA, dopamine, and glutamate.
These chemicals play a key role in whether we feel happy, energetic, and have a positive mental outlook or whether we feel anxious, fatigued, and hopeless.
At least in mice, this approach seems to work. Administering certain strains of probiotics to mice alters levels of neurotransmitters that affect mood and reduce signs of anxiety and depression in mice. It’s still not clear whether humans get the same benefits and which bacterial strains in what amounts are optimal for mental health.
Still, small studies in humans look optimistic. In one study, researchers gave humans a strain of Bifidobacterium called Bifidobacterium longum for 4 weeks. The participants reported feeling less stress, and they enjoyed some improvements in memory.
Another study found that a combination of two strains of Bifidobacterium longum and Lactobacillus helveticus improved symptoms of anxiety and depression in healthy individuals. Some research shows that giving depressed individuals certain bacterial strains lowers cortisol, a stress hormone linked with anxiety and mood disturbances.
What might be the worst for mental health is to have no microbiome. Mice that grow up in a sterile environment and don’t have a microbiome experience more signs of stress. However, when you give them the equivalent of psychobiotics, they become calmer and less stressed.
If the same is true of humans, giving psychobiotics could be a low-risk way to treat the symptoms of depression without resorting to anti-depressants and their side effects.
The Bottom Line
Psychobiotics is a new approach to treating the symptoms of depression, and an important one.
Prescription anti-depressants have a variety of side effects and are best suited for mild-to-moderate cases of depression. Some people don’t respond to any of the anti-depressants currently available and have treatment-resistant depression.
Psychobiotics could offer a new and innovative approach to helping people get relief from the debilitating symptoms of depression. More research is needed, but it looks optimistic!
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