Lately, probiotics have become pretty well-known in media health reports as crucial bacteria and yeasts that thrive in, and benefit, your digestive system. Unlike the bad bacteria that can cause colds and other diseases, probiotics are the good guys; the beneficial bacteria that are necessary to maintaining good health.

Probiotics help treat irritable bowel syndrome, infectious diarrhea, (potentially) some skin conditions, as well as aiding oral health. They’re often found in Greek yogurts and can also be ingested in supplement form to help maintain balance in your gut. While plenty of research shows their value in keeping your gut healthy, there hasn't been enough research looking into their overall health benefits. But now scientists are beginning to grasp what those are.

A new study out of the Leiden Institute of Brain and Cognition at Leiden University in the Netherlands suggests that probiotics may actually aid in improving mood. They might be a good way to fight anxiety or depression, or simply make you feel better after a bad day.

The researchers examined 40 healthy young adults who had no mood disorders. Half of them consumed a powdered probiotic supplement every night for four weeks. The probiotic supplement was called Ecologic Barrier, and contains eight types of bacteria, such as Bifidobacterium, Lactobacillus, and Lactococcus (these three types of bacteria that have been shown in the past to mitigate anxiety and depression). The other half of the participants took a placebo, although they thought they were taking probiotics.

The people who took probiotic supplements began to see improvements in their moods; they reported less reactivity to sad moods than those who took placebos. In other words, the people who took probiotic supplements were better able to overcome sad moods than the others, and thus had fewer depressive thoughts following bouts of sadness.

“Even if preliminary, these results provide the first evidence that the intake of probiotics may help reduce negative thoughts associated with sad mood,” said Lorenza S. Colzato, an author of the study, according to Time. “As such, our findings shed an interesting new light on the potential of probiotics to serve as adjuvant or preventive therapy for depression.”

According to a 2013 study that investigated the link between intestinal bacteria and mental health, not much is known about the ways that the gastrointestinal tract influences mood and behavioral disorders. The authors note that there was scientific interest in this link in the early 20th century, but there hasn't been much research until recently. One of those recent studies examined this link and found that people who took probiotics experienced lower levels of anxiety and depression, and had lower levels of cortisol — the stress hormone — in their saliva when they woke up in the morning.

However, more research will be needed to decide whether taking probiotic supplements can actually improve mood. In the meantime, eat your Greek yogurt daily to keep your gut bacteria happy, and who knows, it might have a positive effect on your mental health too.

Source: Steenbergen L, Sellaro R, van Hemert S, Bosch J, Colzato L. A randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to sad mood. Brain, Behavior, and Immunity, 2015.