Probiotics May Ease Depression Symptoms

Probiotic supplements taken in combination with antidepressants may improve symptoms in people with major depressive disorder, a small study suggests.

Increasing evidence associates the disbalance of the gut microbiota — the community of microorganisms inhabiting the gut — with mental illnesses, such as anxiety and depression.

As six in ten people (60%) with major depressive disorder (MDD) experience some degree of nonresponse to first-line treatments, the researchers at King's College London investigated whether balance-restoring probiotics can help with depressive symptoms.

They found that probiotic intake for eight weeks resulted in more significant improvements in depressive and anxiety symptoms compared with placebo.

"The gut-brain axis is a truly fascinating and rapidly evolving area of microbiome research. The findings of this pilot study are an important step forward in our understanding of the role of probiotics in mood and mental health," says Viktoriya Nikolova, the study's first author from King's IoPPN.

Improvements in depression, anxiety

The study that appeared in JAMA Psychiatry examined 49 participants aged 18 to 55 years with MDD taking antidepressant medication but having an incomplete response. Nearly half (21) also met the criteria of generalized anxiety disorder.

A total of 24 participants were randomized to probiotics containing 14 strains of bacteria at a dose of eight billion colony-forming units per day and 25 to placebo for eight weeks. All participants were asked to continue antidepressant medication. For most (45), it was a selective serotonin-reuptake inhibitor (SSRI).

The probiotic effect on MDD symptoms was measured using gold standard rating scales to screen for anxiety and depression, as well as to estimate its severity and response to treatment. These included the Hamilton Depression Rating Scale (HAMD-17), Inventory of Depressive Symptomatology (IDS), Hamilton Anxiety Rating Scale (HAMA), and General Anxiety Disorder scores (GAD-7).

The study demonstrated that compared to the placebo group, the participants taking probiotics saw greater improvements in depressive symptoms according to HAMD-17, IDS, and HAMA scores but not GAD-7 scores.

None of the participants experienced serious adverse reactions, while 16 people in the probiotic group reported mild and temporary nausea and indigestion. Over time, gastrointestinal symptom scores decreased in both groups, but there was no significant difference between the probiotic and the placebo groups.

Nevertheless, it remains unclear whether probiotics help to alleviate MDD symptoms only when taken with SSRIs or with other treatments as well.

According to a 2020 review of seven studies, 11 of 12 of the different probiotics investigated were potentially useful in significantly reducing anxiety symptoms or improving clinically relevant changes in biochemical measures of anxiety and/or depression.

However, all these studies lasted for short periods and each included a small number of participants, preventing the review authors from drawing any firm conclusions about the overall effects. They hypothesized probiotics might help direct the action of tryptophan, a chemical thought to be important in the gut-brain axis in psychiatric disorders.

The new study finds that eight-week treatment with multi-strain probiotics is well tolerated among adults with MDD and may help to improve depressive symptoms. Still, the findings require further investigation in larger populations.

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