Probiotics, taken alone or with prebiotics, could help ease depression, according to a new paper published in the journal BMJ Nutrition Prevention & Health.

Although the underlying mechanism is still unclear, the study researchers said probiotics might help reduce the secretion of certain inflammatory chemicals, including cytokines.

They also said probiotics might help direct the action of tryptophan, an essential amino acid found in the gut-brain axis in mental health disorders.

Probiotics are the foods that help broaden the profile of good bacteria in the gut and prebiotics are those that help these gut bacteria to flourish.

The gut-brain axis is a two-way relationship that exists between the brain and the gastrointestinal tract. So, the possibility that the gut microbiome might help treat psychiatric illnesses has helped doctors to take a special interest in the topic.

The researchers looked for relevant studies published from 2003 to 2019, which were associated with the potential therapeutic effects of probiotics and prebiotics in adults with mental health disorders, such as depression and anxiety disorders.

They found that 12 probiotic strains featured in the selected studies, especially Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidium, while one study looked at a combination of probiotics and prebiotics.

Every study concluded that probiotics taken either alone or in combination with prebiotics were associated with measurable reductions in the symptoms of depression.

Also, all of the studies showed a significant improvement in the symptoms of anxiety disorder or clinically relevant changes in biochemical measures of anxiety disorders and depression with probiotics alone or combined use.

However, the researchers noted that their reviews have a few limitations. No studies lasted very long and the number of participants was small, making it a bit difficult to come to any strong conclusions about the overall effects of probiotics on mental health.

Still, based on the preliminary evidence, the researchers said further investigation is required to study the effects of probiotics and prebiotics on psychological issues.

Depression and anxiety disorders require different treatment approaches given that they affect people in different ways. They wrote, “In this way, with a better understanding of the mechanisms, probiotics may prove to be a useful tool across a wide range of conditions.”

In addition, they noted that people with depression and anxiety disorders often have other underlying conditions, such as irritable bowel syndrome (IBS) and impaired insulin production.” They wrote, “As such, the effect that probiotics have on patients with [common mental disorders] may be twofold: they may directly improve depression in line with the observed findings of this review, and/or they might beneficially impact a patient’s experience of their [common mental disorders] by alleviating additional comorbidities.”