It has been known for some time that the microbiome, the colony of bacteria that resides in the gut, might help treat mental illnesses thanks to the two-way relationship that exists between the brain and digestive tract, known as the gut-brain axis.
Now, a metastudy published between 2003 and 2019 carried out by researchers at Brighton and Sussex Medical School has found that probiotics, compounds found in foods such as yoghurt, sauerkraut and kimchi that broaden the profile of helpful bacteria in the gut, may help ease the symptoms of depression.
The team gathered together 71 studies, with seven meeting all of their criteria. All of them investigated at least one probiotic strain; four looked at the effect of combinations of multiple strains. In all, 12 probiotic strains featured in the selected studies, primarily Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidum.
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The studies varied widely in their design, in the methods used, and in their clinical considerations, but all of them concluded that probiotic supplements may be linked to measurable reductions in depression.
The effect could be down to probiotics helping to reduce the production of inflammatory chemicals, or they maybe by affecting the action of tryptophan, a chemical thought to be important in the gut-brain axis in psychiatric disorders, the researchers say.
The researchers, however, highlighted several caveats: none of the included studies lasted very long; and the number of participants in each was small. It is also difficult to say if the effects are long-lasting, or whether there might be any unwanted side effects associated with prolonged use.
Nevertheless, on the basis of the preliminary evidence to date, probiotic therapy warrant further investigation, the researchers say.
Reader Q&A: What are the most successful therapies for depression?
Asked by: Serena Collins, Reading
There’s no simple answer because success depends on age, sex, the type of depression and whether it’s combined with anxiety or other mental-health problems. Generally, however, therapies based on exploring and changing the patient’s own thoughts and behaviour are far more effective than old-fashioned talking therapies such as psychoanalysis.
Alternative therapies, although popular, also fare badly. One meta-analysis combined many studies and found that cognitive behavioural therapy (CBT) did best, especially with long sessions. But a newer therapy called behavioural activation also did well.
These are both based on the idea that depression is made worse by adopting the wrong coping strategies. So patients are helped to understand what triggers their depression and how their reactions to life’s events affect their moods and emotions. Learning to replace bad coping strategies, such as drugs, drink and endless rumination, with positive coping strategies can help, either used alone or in combination with medication.