Though the evidence of the role of diet and the gut in the development of psychological disorders is established and growing, the majority of the research has either been epidemiological (observations of large groups of people – these do not show causality) or animals trials (show the mechanisms but might not completely translate to humans). At the end of all of these papers the authors remark that more high-quality human trials are required to draw firmer conclusions. Earlier in the year we had the publication of the SMILES Trial, a study that showed a cause and effect relationship between poor diet and depression and now a new paper provides more good evidence of the role of probiotics and the gut microbiome on mental health. Even more interesting is that this was not even the main aim of the research.

Researchers in New Zealand set up a trial to see whether giving pregnant women probiotics would affect their children’s risk of developing eczema. Eczema is an inflammatory skin condition and the gut microbiome plays an essential role in regulating inflammation. A baby’s gut microbiome is seeded at birth during its transit through the birth canal, or from skin contact after delivery by caesarean section. In the study 423 pregnant women were randomly assigned to two groups. One group received a daily supplement of a strain of bacteria called Lactobacillus rhamnosus (HN001). The other group received an identical looking/tasting placebo. The women took the supplement/placebo from the moment they enrolled until their child was born, and from birth until 6 months if the mother was breastfeeding. Information about the women’s mental state was taken at baseline (14-16 weeks pregnant), when the child was 6 months and 12 months old. They found a strong effect of the probiotic. The women who had taken the supplement (and none of the women knew whether they were taking the active supplement or the placebo) were much less likely to experience depression and anxiety after the birth of their children.

The researchers report that between 10%-15% of women experience post-partum (post-natal) depression, which can impair the development of a strong bond between mother and infant, creating psychological and physical health risks for both. Medication options for breastfeeding women are limited because of the risk that the medication would be ingested by the baby in breast milk. In addition, it is practically difficult for women to access psychological or psychosocial interventions on top of the demands of a new baby. Further, some women feel reluctant to ask for help because they feel ashamed or guilty that they should feel so unhappy following the birth of their baby. Clearly then, the development of accessible and effective treatments is essential. There are many questions still to be answered about what a probiotic treatment might look like. This trial looked at only one strain and it might be that others of a combination are important too. We also need to know how long treatment should last and what the dose should be. But this well-designed study adds to the evidence of the role and importance of gut health in mental health and of taking the health of the whole body in to consideration when looking to treat mental health problems.

Reference

Effect of Lactobacillus rhamnosus HN001 in Pregnancy on Postpartum Symptoms of Depression and Anxiety: A Randomised Double-blind Placebo-controlled Trial. DOI: 10.1016/j.ebiom.2017.09.013

Many by now will be familiar with the term ‘friendly bacteria’, referring to the vast population of bacteria in the digestive tract. This population of microbes (the microbiome) play an important role in maintaining our digestive health and many people consume yogurt and other fermented milk drinks to promote gut health. Increasingly research is showing us that the gut microbiome has a significant effect on our mental as well as physical health.

To gain a better overview of the current status of research in this area a systemic review of random controlled trials was conducted and published in the Journal of Neurogastroenterology & Motility. The researchers reviewed 25 animal and 15 human trials. Of the studies involving human participants just over half described significant effects of probiotics on central nervous system function and an intake of probiotics for four weeks appeared to be the threshold for noticeable effects. In the human trials the most common bacterial strains tested were Bifidobacterium longum, B. breve, B. infantis, Lactobacillus helveticus, L. rhamnosus, L. plantarum, and L. casei, all of which are present in fermented foods such as yogurt, kefir and traditional (unpasteurised) sauerkraut.

Looking at both the animal models and human trials the results of this review indicated that probiotics were an effective intervention for a range of mental health disorders including anxiety, depression, Obsessive Compulsive Disorder (OCD) and memory function. A number of potential mechanisms were identified:

Reduced cortisol (stress hormone) levels
Reduced inflammation.
Improved immune function

It is also feasible that some of the known metabolites of the microbiome such as GABA, an inhibitory neurotransmitter, might play a role either via the vagus nerve or more directly by crossing the blood-brain barrier. Whilst the review is generally positive the researchers called for further studies to be conducted with human participants in order to be able to draw firmer conclusions on the promising role of probiotics on mental diseases.

Reference:

Wang, H., Lee, I., Braun, C. & Enck, P. (2016). Effect of Probiotics on Central Nervous System Functions in Animals and Humans: A Systematic Review. Journal of Neurogastroenterology & Motility, 22, 589-605.