Probiotics, Depression and Anxiety: A New Meta-analysis

One of the more common questions I get asked is “what probiotics are good for my condition?”  Believe me, it does not make me happy to have to say, over and over again, “If only we knew.”

I am always glad, therefore, to read something that gives at least a smidge of information on specific species that may help a specified condition.  A couple of weeks ago, Gut Microbiotia for Health published a post about recent research out of Brown University that at least gives us a better idea of what might work for depression and anxiety.[i]  As these are two of the most common illnesses currently affecting those of us in the industrialized world, well…the more we know, the better.

These researchers conducted a meta-analysis of 34 different clinical trials, to try to pinpoint what we currently know.  Such analyses previously done of existing clinical trials have, to date, used too few studies to be of much use and worse, they often combined diagnoses, like depression and anxiety, when looking at outcomes, confusing results.  7 of the trials they looked at tested prebiotics and the other 27 used probiotics or synbiotics (combinations of pro- and pre-biotics).


They found that using prebiotics alone (for periods ranging from 4 hours to 4 weeks) did not make any difference in the symptoms of anxiety or depression.

However, in the 23 trials that looked at depression and 22 trials that looked at anxiety, the studies showed a trend:  “…the administration of probiotics—including Bifidobacterium longum, Bacillus coagulans, and Lactobacillus alone or in combination with Bifidobacterium—from 8 to 45 weeks led to small but significant antidepressant and antianxiety effects.”

Overall though, these scientists found that improvement was not seen in anxiety or depression using Lactobacillus species alone.  To be effective, they needed to be combined with Bifido species.

One of the things that really struck me was the fact that results are likely worse than they should be because most of the trials were conducted on people who were healthy, not on those with depression or anxiety.  Only 4 of these trials were actually conducted on those affected with these issues, a phenomenon I’ve actually made mention of before in a post I wrote on depression and probiotics back in October of last year.  Why you would test these as treatments for illnesses in people without the illnesses is incomprehensible to me…but what do I know?!  In that October post, which was a general update on what we now know about using probiotics in depression, I also mention (for the 2nd time – this is now the 3rd!) what is still considered one of the most significant studies to date:  an 8 week long double-blind, placebo controlled trial of probiotics on 40 people with major depressive disorder.  In that study, the researchers used 2 billion units each of Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidum. The probiotic made a significant improvement in depressive scores.  Today’s article from Gut Microbiota for Health, also makes note of this particular study.   And notice that in this successful clinical trial, the Lactobacilli were indeed mixed with Bifido bacteria.

Overall, the news is good.  While obviously much more research needs to be done, and we don’t yet know optimal species or doses, we at least know that something out there in this realm seems to work.  As these scientists write, “There is general support for antidepressant and anxiolytic effects of probiotics, but the pooled effects were reduced by the paucity of trials with clinical samples. Additional randomized clinical trials with psychiatric samples are necessary fully to evaluate their therapeutic potential.”[ii]



[ii] Liu, RT, Walsh, RFL, Sheehan, AE.  Prebiotics and probiotics for depression and anxiety: a systematic review and meta-analysis of controlled clinical trials. Neuroscience & Behavioral Reviews. 2019. 102:13-23.

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