A spoonful of various supplements and probiotics on a gray surfaceShare on Pinterest
Probiotics may aid the effectiveness of mental health treatments, according to new research. FreshSplash/Getty Images
  • New research has shown that people with major depressive disorder who took probiotic supplements along with standard antidepressant medication had reduced symptoms.
  • The findings suggest that probiotic supplementation could help adults with depression as a complementary therapy, but further research is required.
  • Experts recommend incorporating probiotic-rich foods such as yogurt, kefir, miso, and tempeh into one’s diet.

Antidepressants are typically the first line of treatment for people with major depressive disorder. However, between 15 and 30% of people with depression don’t respond to these medications.

According to a new study published in JAMA Psychiatry, individuals with major depressive disorder (MDD) who took probiotic supplements containing 14 strains of bacteria demonstrated reduced symptoms of depression and anxiety.

The eight-week, double-blind, randomized placebo-controlled trial was conducted by researchers from the Institute of Psychiatry, Psychology & Neuroscience at King’s College London in collaboration with ADM Protexin.

Researchers wanted to explore the connection between improving gut health — specifically probiotic supplementation — and its effect on mental health.

They examined 50 outpatients diagnosed with major depressive disorder who scored higher than 13 on the Hamilton Depression Rating Scale (HAMD-17). Over the course of the study, participants took antidepressants for six or more weeks and were instructed not to make changes.

In this study, 49 adults with major depressive disorder who did not respond to prescription antidepressants were given a 14-strain blend probiotic supplement or an identical placebo. Twenty-four participants took the probiotic.

While both groups showed improvement in their symptoms during the study, more improvements were observed in the probiotic group from the fourth week onward.

“One particularly interesting finding was the change in anxiety scores, which have rarely been explored in studies of probiotics in depression,” said Dr. Nikolova, the study’s lead author from the Institute of Psychiatry, Psychology & Neuroscience at King’s College London, speaking to Medical News Today.

“This study 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 currently taking antidepressants.”

— Dr. Viktoriya Nikolova, lead study author

The promising results have resulted in the planning of a larger follow-up trial.

“Given the exciting results seen in this trial, a larger follow-up trial is currently being planned by Professor Stone, the study’s senior investigator, but this has not yet been confirmed,” Dr. Nikolova added.

“Our understanding of the gut microbiome and its impact on mental health is still in its infancy,” said Dr. Benjamin Lerner, a gastroenterologist at Bridgeport Hospital and assistant professor of digestive diseases at the Yale School of Medicine, who was not involved in the study.

“We know that the human body is home to trillions of microorganisms, the majority of which live inside the gut; we know that these microorganisms affect digestion, metabolism, and inflammation; and we know that the brain and digestive system communicate via neural and hormonal signals, collectively referred to as the gut-brain axis,” he explained.

Still, it’s important to note that there is still much to learn about the biological complexities of mental health and the gut microbiome.

“The human brain and the gut microbiome are two of the most complex biological systems. They almost certainly influence each another in multiple ways, probably simultaneously,” Dr. Lerner said.

Research supports the idea that probiotic supplementation could be an effective treatment method to alter gut and brain interactions.

“The gut-brain axis is a concept that proposes a correlation between the intestinal microbiota and the neuroendocrine-immune pathways,” said Kelsey Costa, a registered dietitian nutritionist and health research specialist.

“Emerging research suggests that this connection is facilitated through an array of physiological and biochemical pathways, such as hormones, the immune system, and metabolic substrates that the microbiota produces,” she said.

Dr. Lerner said the mechanism of how probiotic supplements may help with depression is still unknown.

“Possible mechanisms include production of neurotransmitters, which can affect mood, and down-regulation of pro-inflammatory signaling molecules, called cytokines,” he said.

The positive physical effects of a healthy gut microbiome can extend to a healthier mental state.

“Probiotic supplements may reduce symptoms of MDD by improving and redistributing microbiota species, maintaining intestinal barrier integrity, and reducing oxidative stress and inflammation. These benefits could extend to positive behavior, mood, sleep, appetite, and cognition changes, improving overall mental health,” Costa said.

“This study adds to a growing body of evidence on the link between the gut microbiome and mental health and is an important step forward in understanding how probiotics can be used to support mental health.”

— Dr. Viktoriya Nikolova, lead study author

The biggest limitation of this study was its small sample size.

“This particular study was quite small, with only 25 participants in each arm. Furthermore, all participants received antidepressants, in addition to probiotics. It is not known whether the findings would hold up in a larger study or whether probiotics would have a positive effect in the absence of an antidepressant,” said Dr. Lerner.

Additionally, not all probiotics are the same.

“Different species and strains are likely to impact the body in different ways,” Dr. Lerner added.

“There are studies that should change how we treat patients, and there are studies that should prompt further research. This is one of those studies that should prompt further research. In short, people [with] depression should be encouraged to seek professional help and not to self-treat with probiotics,” he said.

There are numerous probiotic-rich foods that people can incorporate into their diets to aid better gut health.

“I favor foods that are naturally rich in probiotics, such as yogurt, sauerkraut, miso, tempeh, and kefir. Good sources of prebiotics (high fiber foods that promote the growth of beneficial bacteria) include whole grains, apples, bananas, onions, garlic, asparagus, and artichokes,” Dr. Lerner said.

Costa, meanwhile, suggested the following foods to increase probiotic intake:

  • Yogurt: Yogurts are one of the most popular probiotic sources in dairy and non-dairy varieties. Widely available commercially, yogurt is an easy and convenient way to add probiotics to your diet.
  • Other dairy foods: Cultured buttermilk, cheese, and other fermented dairy products such as kefir are also common sources of probiotics.
  • Non-dairy foods: Excellent non-dairy options include probiotic-rich foods like miso, tempeh, sauerkraut, kimchi, natto, and pickles. You may also find probiotic strains in fermented cereals, legumes, maize, pearl millet, and sorghum.

Kombucha is a popular probiotic-rich drink made from tea that has been fermented with yeast and bacteria. Other non-dairy fermented drinks, such as coconut kefir, are becoming more widely available.