Obsessive-compulsive disorder (OCD) affects up to 3 percent of people worldwide and remains one of the most challenging mental health conditions to treat effectively.
That makes any fresh insight into OCD’s root causes especially valuable – like a new study pointing to a surprising suspect: the bacteria living in our gut.
The research from China explored how the gut microbiota – the complex community of bacteria that live in the digestive system – may influence whether a person develops OCD, and identified six types of bacteria that appear to be linked with the condition.
A steady stream of studies has shown close connections between the brain and the gut, but this is the first to provide compelling evidence that gut bacteria may actually help cause it. The researchers used genetic data to strengthen the case for causation.
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“Previous studies have indicated a potential link between the gut microbiota and OCD,” write the researchers from Chongqing Medical University in their published paper. “However, the exact causal relationship remains uncertain.”
“Our analysis suggested that specific gut microbiota might have a causal relationship with OCD, revealing potential intervention strategies for the prevention and treatment of this disorder.”
To explore this link, the researchers used a genetic approach known as Mendelian randomization, which allows scientists to infer causality by analyzing genetic variants that influence both OCD and gut bacteria.
They assessed links between genetic data and gut bacteria in a sample of 18,340 people, and the links between genetic data and OCD in a separate sample of 199,169 people.
Although these were two discrete sets of data, the study used Mendelian randomization to essentially bridge the gap and connect gut bacteria patterns with OCD.
Because our genes are fixed at birth and not shaped by environment or lifestyle, this method helps strengthen the case that gut bacteria might directly contribute to OCD, rather than just being an effect of it.
However, more data and more controlled experiments will be needed to confirm a causal link.
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Three types of bacteria appeared to be protective against OCD: Proteobacteria, Ruminococcaceae, and Bilophila. Another three seemed to increase the risk of OCD: Bacillales, Eubacterium, and Lachnospiraceae UCG001.
Interestingly, many of these bacteria have been linked with the brain before. For example, previous studies have found a connection between low levels of Ruminococcaceae species and depression. These findings expand what we already know about the gut-brain axis and how one can affect the other.
“Future research should employ longitudinal designs and diverse populations to validate and expand upon these findings, as well as a more in-depth classification of microbes and their metabolic products, to further understand the role of gut microbiota in OCD,” write the researchers.
Down the line – and it’s still a way off – we may have a new way to treat or prevent OCD, by controlling gut bacteria mixtures. For people living with the condition – and the families, friends, and clinicians who support them – this could eventually offer new hope.
“Despite the utilization of cognitive behavioral therapy and selective serotonin reuptake inhibitors in OCD treatment, a notable 25–40 percent of patients experience suboptimal or no response to these interventions,” write the researchers.
“Moreover, the personal and societal toll of OCD is substantial.”
The research has been published in the Journal of Affective Disorders.
