Reports in the past few years suggest that probiotics – the good bacteria you find in a cup of yogurt with “live and active culture” – can lower anxiety and improve your mood by actually altering your brain chemistry. As it turns out, this may be just another tale of mice and men.
Research with mice
In 2011, as reported in many mainstream media outlets, researchers from the Alimentary Pharmabiotic Center at University College Cork, Ireland, published a study suggesting that probiotics have a direct impact on stress hormones and mood neurotransmitters in mice.
The researchers were studying a strain of beneficial probiotic called Lactobacillus rhamnosus, which is found in some yogurts. They fed half the mice in the study the probiotic and the other half broth.
Measuring their stress
Then the researchers gave the mice a "behavioral despair" test, the primary method for evaluating antidepressants in the field. They dropped the mice into room-temperature water in a narrow cylinder from which they couldn't escape and observed their behavior. Mice can swim, but they don’t like it.
The mice that ate broth swam around trying to get out of the water for an average of four minutes, after which they reached a "depressed state" and simply gave up. The other group of mice, the ones fed L. rhamnosus, didn’t give up so easily. Their average swim time was six minutes before they were plucked from the water.
‘More chilled out’
Later, lab experiments with the mice that gave up revealed a huge spike in a stress hormone called corticosterone. The mice that continued swimming had half as much corticosterone. These mice also had changes in a neurotransmitter in their brains called GABA (γ-aminobutyric acid) that were similar to changes caused by antianxiety medications.
In other words, the researchers concluded the mice that were fed L. rhamnosus and swam longer in their watery trap were acting as if they were on Valium.
"These mice were more chilled out," said pharmacologist and lead researcher John Cryan.
At least four more preclinical studies in mice have followed Cryan's study. All support the suggestion that probiotics have an effect on brain function through what is called the "brain-gut axis." In fact, in 2013, the term "psychobiotics" was coined to define the type of bacteria that may produce a positive mental health benefit when ingested in adequate amounts.
Next, research with humans
This year, however, Cryan and his colleagues published research in humans with quite different results. "We aimed to examine if these promising preclinical findings could be translated to healthy human volunteers," the researchers stated in their study, published in March in the journal Brain, Behavior, and Immunity.
In the eight-week trial, 29 healthy male volunteers either received no treatment (a "placebo" cornstarch pill) or a pill containing a small colony of L. rhamnosus. The volunteers completed numerous tests, including physical stress tests and measurements of brain chemicals.
Another cold-water test
For one test, participants were required to avoid alcohol for 24 hours, strenuous exercise from 2 p.m. the day before and caffeinated beverages on the day of the stress procedure. They also fasted for two hours before testing. Then, for the test, they immersed a hand in ice-cold water for a minute while their stress levels were measured, both objectively and by their own description.
Among the volunteers who received the psychobiotic pill, there was no overall effect on measurements of mood, anxiety, stress or sleep quality compared to the group who took the starch pill.
"These findings highlight the challenges associated with moving promising preclinical studies, conducted in an anxious mouse strain, to healthy human participants," the researchers concluded.
Promising research in this area may yet result in new treatments related to probiotics and brain chemistry. Several studies suggest that probiotic treatment in people with irritable bowel syndrome can improve patients' moods.
In a study in May in the journal Reviews in the Neurosciences, researchers looked at the link between gut bacteria and mood disorders to determine whether there is potential for new treatments for bipolar disorder. While the field is promising, they determined, further investigation is required.
We've written about probiotics before. For a good article on the benefits of probiotics and their activity in the body, click here.
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