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June 20, 2023

Can probiotics help with depression? Link between mental health, gut bacteria points to benefits

The food supplements are widely used as a digestive aid. New research shows they hold promise for emotional wellness, too

Mental Health Depression
Probiotics Depression Anxiety Andrew Neel/Pexels

Probiotics show promise as possible aids in the treatment of depression and anxiety, new research shows. The food supplements commonly used for digestiion are thought to benefit the pathways connecting the brain and gut.

The relationship between mental health and the gut is something most people are able to feel in times of stress and anxiety; it's common to experience nausea alongside nervousness when under pressure, for example. But could we potentially prime our intestines in order to regulate moods?

Probiotics have become popular supplements used to aid digestion by maintaining healthy gut bacteria. Emerging research suggests they also could be helpful in treating depression and anxiety.

The human intestinal tract contains millions of microorganisms collectively known as the gut microbiome, which includes a mix of bacteria, viruses and fungi. Millions of nerve cells that line the gastrointestinal tract communicate with the brain, forming what's called the gut-brain axis.

Exploration of the link between emotions and gut health has been spurred by research into digestive disorders such as irritable bowel syndrome. IBS is known to destabilize the balance of gut bacteria, increasing the risk of depression and anxiety. More common issues like constipation, diarrhea, bloating and upset stomach also can trigger emotional responsesAbout 30-40% of people have functional bowel problems at some point, which elevates the risk of developing depression and anxiety, said Jay Pasricha, former director of the Johns Hopkins Center for Neurogastroenterology

Historically, the link between mental health and the gut was thought to flow primarily from the brain to the gut.

“For decades, researchers and doctors thought that anxiety and depression contributed to these problems," said Pasricha of his research into the brain-gut connection. "But our studies and others show that it may also be the other way around."

Probiotics are considered food supplements. They're generally used to boost the body's immune system, promote antimicrobial substances in the gut and ferment fiber that creates nutrients for the cells that line the intestines. 

Foods like yogurt and kimchi naturally contain probiotics, but other strains can also be taken in powder or pill form. Probiotics are not regulated by the U.S. Food & Drug Administration, which means their quality and effectiveness may vary depending on the source. And since each person has unique gut bacteria based on personal combinations of diet and genetic factors, the same probiotics will not affect everyone equally.

Despite these caveats, there is promise in the idea that probiotics can be used to boost mental health and help manage emotions.

In a new study published in JAMA Psychiatry, probiotic supplements were given to people taking antidepressants for major depressive disorder; around half of them also had been diagnosed with generalized anxiety disorder. The goal was to see whether the supplements would help alleviate depression and anxiety symptoms over an eight-week period. 

Among 49 study patients, 24 were given a probiotic and the rest were given a placebo. All of the study participants had taken antidepressants for six weeks or more without emotional improvement. They had been instructed to continue taking them without any changes during the study. The probiotic used in the study contained 14 strains of bacteria that are commonly found in a range of supplements used for digestion and gut health.

Researchers found that both groups of patients improved during the study, but those who took the probiotic had better results after four weeks, including reduced depression symptoms and anxiety levels.

The study was conducted by the Institute of Psychiatry, Psychology & Neuroscience at King’s College London in collaboration with ADM Protexin, a U.K.-based supplement and probiotic manufacturer. It is one of the first trials in a Western population to show both good tolerability of probiotics and positive effects on mental health in adults with depression who are currently taking antidepressants, the researchers said. It builds on previous research that has shown that probiotics can help with depression. 

One of the motivations for the study is the high rate of persistent depression symptoms among people who take antidepressants. About 60% of people with major depressive disorder have some level of nonresponse to these drugs, and roughly one-third continue to experience symptoms despite further treatment, the researchers said. The majority of patients in this study were taking drugs in the class of antidepressants known as selective serotonin-reuptake inhibitors, which are the most commonly prescribed medications for depression.

The researchers noted that one limitation of the study is the inability to determine whether the effects of the probiotics were independent or linked to their interactions with SSRIs. Also, certain groups — such as those with bipolar disorder, eating disorders, personality disorders and substance use disorders — were excluded from the study.

Since more research is needed on the effectiveness of probiotics for managing mood, it's not recommended to abandon other prescribed treatments for mental health conditions in favor of probiotics. But since probiotics are generally considered safe and beneficial for gut health, it may be worth trying them daily for a month to see whether they have emotional benefits, Johns Hopkins researchers say.

The King’s College London study will open the door for larger studies to evaluate how probiotics can be used therapeutically for a range of mental health issues.

"The gut-brain axis is a truly fascinating and rapidly evolving area of microbiome research," Nikolova said. "The findings of this pilot study are an important step forward in our understanding of the role of probiotics in mood and mental health."

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