A new study looking at the gut bacteria of over 1,000 people in Belgium has found a possible link between certain types of bacteria and depression.
The study published today in Nature Microbiology combined data from the microbiomes of 1,054 people enrolled in the Flemish Gut Flora project with self-reported and physician-diagnosed depression data. Using bioinformatics analyses, the researchers were able to identify certain groups of bacteria, which were either positively or negatively correlated with mental health.
Two groups of bacteria in particular, Coprococcus and Dialister, were consistently found to be at low numbers in people with depression. The scientists then checked their findings on another cohort of 1,063 people involved in a similar study in The Netherlands and found the same result.
“This is the first time this kind of work has been done in such a large scale in humans. Most previous work has been done in animal models,” said Jeroen Raes, Professor at the Catholic University of Leuven in Belgium and Flemish Institute of Biotechnology and lead author of the study.
The research also suggests that some bacterial species in the microbiome may be able to produce or breakdown molecules that interact with the human nervous system. They looked at bacterial DNA from fecal samples in a subset of the study group, finding that the gut microbiome may be able to synthesize molecules such as seratonin and dopamine, which are found in abnormal levels in people with depression. People with treatment-resistant depression had microbiomes that were less-likely to be able to synthesize these molecules than people without depression.
“We don’t yet know whether these neuroactive compounds produced in the gut can reach the brain. Can they traverse the blood-brain-barrier? Or perhaps they act directly on the vague nerve in the stomach, which sends signals directly to the brain,” said Raes.
Raes is very keen to point out that all of this work still has to be done and there are many unknowns, but there are plans underway to figure some of them out.
“Our goal would be to isolate these specific bacteria and culture them in animal models to see if they elicit or change behavioral traits. If this is proven then they next step would be to set up human trials to see if procuring these bacteria can improve symptoms in people with depression,” said Raes.
There are also a few limitations to the current study. The researchers looked at thousands of microbiomes in Europe and the results are likely to be applicable throughout the Western world, but it is currently not known whether this extends to places such as Asia and Africa, due to different diets.
Despite this, the sheer number of people involved in the study and the analysis methods used make it a formidable piece of work showing that the microbiome is likely to be related to mental health.
“This is a creative and wholistic approach to the complex human biology of depression. We need to follow every thread that relates to depression spanning genetics, imaging, psychotherapy and more novel angles such as this. I look forward to learning more about this work,” said Ken Duckworth M.D., medical director of the National Alliance on Mental Illness.
The microbiome is undoubtedly one of the hottest topics in medical research at the moment, having been linked to numerous diseases such as multiple sclerosis and even childhood leukemia. The world’s largest cancer charity, Cancer Research UK also recently staked $ 25 million on an ambitous research project led by scientists at Harvard Medical School and the Dana Faber Cancer Institute to uncover links between the microbiome and colorectal cancer. And the research papers delving more in to the microbiome are coming thick and fast.
“I’m amazed by the breadth of diseases that the microbiome has been associated with. Although I’m a believer that the microbiome is likely to be involved in many diseases, I don’t necessarily think all of the early studies will be replicated,” said Raes.
Another study also published today in Nature Biotechnology by a different group of scientists has discovered over 100 brand new bacterial species in the human gut. The reseachers sequenced bacteria from samples of feces given by 20 people from the UK and Canada and found 273 seperate bacterial species. The work has contributed to a considerable and growing database of the composition of the human microbiome.
“At this moment there is not enough evidence to say that modulating the microbiome is a treatment for depression. However, general healthy advice never hurts. The gut microbiome is always helped by a good diet full of fibre and lots of varied fruits and vegetables,” said Raes.