Researchers found that seniors with depression who took a daily probiotic alongside their regular antidepressant treatment experienced modest but meaningful improvements in depression and anxiety symptoms compared with those who received a placebo. A placebo is an inactive treatment designed to look identical to the real one.

The study was published in the Journal of the American Geriatrics Society.

Exploring the Gut-Brain Connection

Scientists have become increasingly interested in the relationship between the digestive system and the brain, often referred to as the gut-brain connection. The trillions of microbes that live in the human digestive tract, collectively known as the gut microbiome, may influence mood, behavior, and mental health through a variety of biological pathways.

Probiotics are live microorganisms that can help support a healthy balance of bacteria in the gut. Researchers have been investigating whether these microbes could potentially complement traditional treatments for conditions such as depression and anxiety.

Inside the Clinical Trial

The pilot study enrolled 58 adults in India who were at least 60 years old and had moderate depression. All participants continued receiving standard antidepressant treatment.

The volunteers were randomly assigned in a 1:1 ratio to receive either a daily probiotic supplement or a placebo for 12 weeks. Researchers then continued monitoring participants for another 12 weeks to track longer-term outcomes.

Importantly, both groups showed substantial improvement over the course of the study. However, the probiotic group experienced somewhat greater reductions in symptoms of depression and anxiety.

Measuring Mental Health and Biological Changes

To evaluate the effects of treatment, researchers used several different tools.

They assessed participants using established psychological rating scales designed to measure depression and anxiety symptoms. They also examined a biomarker known as (serum brain-derived neurotropic factor level). Brain-derived neurotrophic factor, often abbreviated as BDNF, is a protein involved in the growth, maintenance, and survival of nerve cells and is frequently studied in mental health research.

In addition, investigators analyzed participants’ gut bacteria through (fecal microbiota profiling), which allows scientists to examine the composition of microbes living in the digestive system.

Taken together, the findings suggested that probiotic therapy contributed to symptom improvement. However, the researchers did not find clear evidence that probiotics produced additional improvements in overall quality of life compared with placebo.

Encouraging Results, But More Research Needed

Because this was a relatively small pilot study, the findings should be viewed as preliminary. Larger studies will be needed to determine how much benefit probiotics may provide, which patients are most likely to respond, and whether the effects remain consistent across broader populations.

Even so, the results support the idea that probiotics could serve as a safe and biologically plausible addition to standard depression treatment.

“The results of our study are novel, and we are now planning a follow-up, larger-scale clinical trial due to the encouraging findings,” said co-corresponding author Dr. Saibal Das, MBBS, MD, DM, PhD, of the Indian Council of Medical Research — National Institute for Research in Bacterial Infections, Kolkata.

“My vision is to develop affordable healthcare solutions and make them available to the larger population for meaningful public health impact,” added co-corresponding author Abhinaba Ghosh, MBBS, MSc, PhD, a physician-neuroscientist from Tata Medical Center, Kolkata.