Probiotics and stress

With the increased research interest in the interactions between the brain and the gut, people are curious whether we can affect the brain in desirable ways by targeting the gut. Existing evidence from France has indicated that taking a probiotic can reduce psychological distress and urinary levels of cortisol (a hormone associated with stress).

Previous research from our own group in animal models indicated that a strain of bacteria-Bif. Longum 1714-could reduce the physiological stress response. The 1714 strain was associated with reduced stress-induced hyperthermia, as well as reduced depression-like behaviour. Given these findings, there was interest in whether the bacteria could have similar stress-reducing effects in humans.

Participants took the probiotic for 4 weeks and the placebo for 4 weeks. (Both came in the form of a white powder that one mixes into milk each morning). Participants filled in daily online questionnaires assessing their perceived stress levels-during probiotic supplementation stress levels started off at a similar level, but were reduced by the final week of taking the probiotic.

So far, the results were similar to what the group in France found. But we took things a step further by seeing how people would respond to a controlled stressor after taking the probiotic. At baseline and following each of the 4 week periods they were exposed to a socially evaluated cold pressor test. One has to immerse one's hand in ice cold water for up to 3 minutes. After taking the probiotic, participants showed lessened cortisol output in response to the stressor. Furthermore, although anxiety levels were heightened by the stressor at all visits, the increase was lessened following the probiotic.

Interesting stuff, but further research will be needed to determine how the bacteria is having these effects-we know that bacteria can produce neurochemicals that affect factors such as mood, but we're still in the early days of trying to work out the process through which this leads to knock-on effects on the brain.

We have presented the findings at conferences such as Neuroscience Ireland and Society for Neuroscience (you can download the relevant posters from the Department of Psychiatry website) and the results  have received coverage in numerous mainstream outlets, including The Guardian and The Huffington Post. As usual, things move a bit more slowly in academia, but we have the research paper out now too-it's open access, so anyone with an internet connection can access it:

Allen, A. P., Hutch, W., Borre, Y. E., Kennedy, P. J., Temko, A., Boylan, G., Murphy, E., Cryan, J.F. Dinan, T.G., & Clarke, G. (2016). Bifidobacterium longum 1714 as a translational psychobiotic: modulation of stress, electrophysiology and neurocognition in healthy volunteers. Translational Psychiatry, 6(11), e939.

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