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One of the most significant recent advances in health sciences is the exciting discovery that the microbiota in your gut communicate with the cognitive and emotional centers of your brain. This discovery is leading some researchers to identify what they are now calling the microbiota-gut-brain axis.
The existence of a microbiota-gut-brain axis suggests the very safe, affordable possibility that taking probiotics the beneficial bacteria in your gut microbiome and getting more of the fiber and prebiotics that feed them, could improve mental health.
Probiotics & the Microbiota
Your body is a wonderous ecosystem. It is a strange thought, but there are nine times as many bacteria living in your digestive tract than there are human cells in your entire body. There are more of them in you than you! And it is populating your digestive tract with good bacteria, or probiotics, that ensures that your microbiota is healthy. It is well known that that helps digestion and immunity. But it is now known that it also means that the communications your microbiota are sending your brain are positive communications that support mental health.
Microbiota-Gut-Brain Axis: The research only in the past couple of years that has begun to establish that your gut and your brain communicate with each other and that the type of bacteria in your gut influences your brain and your cognitive and emotional health (Nat Rev Microbiol. 2021 Apr;19(4):241-255).
A 2023 study of 206 women found that positive emotions and beneficial emotional strategies are linked to a beneficial microbiome diversity (Psychol Med. 2023 Mar 21;1-10).
In 2015, a triple-blind study of healthy people found that probiotics significantly reduce negative thoughts associated with a sad mood compared to placebo. The positive effect was mostly because of reduced rumination and aggressive thoughts. It was the first ever evidence that probiotics can reduce negative thinking associated with sadness (Brain Behav Immun 2015;48:258-64).
Probiotics & Depression
In 2007, researchers made the early discovery that people with more depression have significantly better improvement in mood on a probiotic than on a placebo (Eur J Clin Nutr 2007;61:355-61). And when 40 people with major depressive disorder were given either a placebo or probiotics for eight weeks, the ones on the probiotics had significantly greater improvement on the Beck Depression Inventory (Nutrition 2016;32(3):315- 20). Other studies have found the same result (Journal of Functional Food 2019;52:596-602).
Another study showed that one month of probiotics significantly improved, not only depression, but anger (Gut Microbes 2011;2:256-61). This is not the only study to find an improvement in both depression and anger. A double-blind study of 38 healthy people found that probiotics significantly improved mood, including depression, anger, fatigue and sleep quality (Front Psychiatry. 2019 ;10:164).
The accumulation of research has now led to a series of meta-analyses. A meta-analysis of 19 double-blind studies demonstrated that probiotics significantly improve depressive symptoms in people with major depressive disorder (Psychiatry Res 2019 Sep 17:112568).
A second meta-analysis of controlled studies again found significant antidepressant effects for probiotics (Neurosci Biobehav Rev. 2019 Apr 17 ;102:13-23).
And a third meta-analysis of seven studies that, for some reason, failed to find that probiotics alone help depression even though it says that lots of studies have found that they do, did find that adding probiotics to antidepressant drugs is significantly more effective than the drugs alone (J Clin Med 2021:10(4):647).
Probiotics & Anxiety
At around the same time the research started to point to probiotics for depression, research started to be published for anxiety too. A 2011 study concluded that probiotics offer significant help to people with anxiety (Gut Microbes 2011;2:256- 61). More recent double-blind research has shown that probiotics are able to improve panic attacks, anxiety, worrying and ability to regulate negative moods in college students (J Affect Disord 2019 Jun 1;252:271-277).
Probiotics can also help test anxiety. 60 students with test anxiety who were studying for an exam were given either a placebo or probiotic for three weeks. If they were given a placebo, their scores got worse. Their anxiety scores increased from 13.27 to 15.3, and their depression scores went from 12.23 to 14.07. When they were given the probiotic, though, the opposite happened. Only in the probiotic group, scores improved. Anxiety dropped from 13.93 to 10.57; depression dropped from 12.37 to 8.17. The probiotic group was also the only one to experience significant improvements in insomnia (Front Immunol. 2023; 14: 1158137).
A meta-analysis of controlled studies now confirms the significant anti-anxiety effects of probiotics (Neurosci Biobehav Rev. 2019 Apr 17;102:13-23).
Probiotics & Stress: If probiotics can improve emotion, depression and anxiety, can they also improve stress? They can. A double-blind study of adults with stress found that probiotics significantly improve both stress and anxiety. The study found that probiotics lower levels of the stress hormone cortisol (Benef Microbes 2019 Apr 19;10(4):355-373). Earlier research had already pointed to this cortisol lowering effect (Gut Microbes 2011;2:256-61).
Probiotics & Insomnia
As the test anxiety study found, probiotics can also help insomnia. A startling earlier study had already found that a blend of lactobacillus and bifidobacterium probiotics could significantly improve sleep quality (Front Psychiatry. 2019;10:164). A recent meta-analysis of 14 studies confirmed it: probiotics significantly improve sleep quality as measured by the Pittsburgh Sleep Quality Index (Eur J Clin Nutr 2020;74:1536-49).
A just published meta-analysis of six controlled studies took a look at the effect of a probiotic called Lactobacillus gasseri on sleep. The 343 people in the studies were all experiencing mild, chronic stress. The meta-analysis revealed that the probiotic supplement significantly improved the global score on the Pittsburgh Sleep Quality Index. Four of the six studies found a significant improvement in at least one score of sleep quality. EEG assessments also found significant improvement in a number of outcomes. This novel meta-analysis shows that taking probiotics can improve sleep and sleep quality in people with mild to moderate stress (Clin Nutr. 2023 Aug;42(8):1314-1321).
All of this research points to the exciting new discovery that the bacteria in your gut are in communication with the cognitive and emotional centers of your brain. So, putting more good bacteria in your gut, means more good messages to your brain. And that’s good news for mental health.VR
Linda Woolven is a master herbalist, acupuncturist and solution-focused counsellor with a virtual practice in Toronto, ON, Canada. Woolven and Ted Snider are the authors of several books on natural health. You can see their books at www.thenaturalpathnewsletter.com. They are also the authors of the natural health newsletter The Natural Path. The Natural Path is a natural health newsletter specifically designed to help health food stores increase their sales by educating their customers. The Natural Path contains no advertising and never mentions a brand name. Retailers can provide The Natural Path Newsletter to their customers. For more information, contact Snider at tedsnider@bell.net or (416) 782-8211.
