A wide variety of micro-organisms, such as bacteria, viruses and yeasts, live on and in the human body. All those microorganisms together are called the microbiome. The microbiome is necessary for optimal physical functioning; for example, through the production of essential nutrients and protection against pathogens. Disturbances in the microbiome increase the risk of numerous diseases. For example, there is increasing evidence that various brain diseases are also related to disturbances in the microbiome. 

Role of the microbiome

These results come from the most extensive study into the relationship between the microbiome and depression, involving 3,211 participants from the HELIUS study (see fact box), led by professor Max Nieuwdorp. This research shows a clear relationship between the composition of the microbiome and depression. A microbiome containing less diverse bacteria, or in which certain bacterial species are underrepresented, was associated with having depression or more depressive symptoms. This association was as strong as established risk factors for depression such as smoking, alcohol consumption, a lack of exercise and being overweight. Influencing the microbiome may therefore be hugely relevant for the treatment of depression. “Now that we know which disturbances in the microbiome are significant for depression, this opens up new possibilities for treatment and prevention. Which is urgently needed,” says Amsterdam Public Health and Amsterdam Neuroscience researcher Anja Lok, psychiatrist and researcher at the Department of Psychiatry at Amsterdam UMC. 

Ethnic differences

Previous research from the HELIUS study has illustrated ethnic differences in both the composition of the microbiome and the occurrence of depression. But until now no connection between the two. Amsterdam Public Health researcher Jos Bosch from the University of Amsterdam's Department of Psychology: “The substantial ethnic differences in depression do indeed appear to be related to ethnic differences in the microbiome. We don't know exactly why this is yet. This association was not caused by differences in lifestyle such as smoking, drinking, weight or exercise, and merits further investigation. For example, diet could play a role.” This is the first study to show that the disparity in depression between population groups is related to the composition of the microbiome. 

Confirmation by Rotterdam study 

It is important to determine whether the relationships found between the microbiome and depression can be confirmed by other studies. In the second article in Nature Communications, by researchers from Erasmus MC, the data from the HELIUS study and ERGO study (see fact box) were compared. This comparison confirmed a consistent association between twelve groups of bacteria and the occurrence of depression. And offered an explanation: the twelve bacterial groups produce substances such as glutamate, butyrate, serotonin and gamma amino butyric acid. These so-called 'neurotransmitters' play an important role in depression. “These results therefore clearly provide direction for future research into possible treatments, such as the use of probiotics, prebiotics and synbiotics or faecal microbiota transplantation as well as changes to lifestyle and diet," says Anja Lok. 

Read both the Helius research on the link between depression and the microbiome as well as the confirmatory ERGO research in Nature Communications.