How Does the Gut Microbiome Differ in People with OCD?

What you need to know

• People with OCD have differences in their gut and throat microbiomes compared to people without OCD
• OCD patients had more bacteria associated with gut inflammation and fewer bacteria linked to dopamine production in their stool samples
• The throat microbiome also showed differences, with OCD patients having a lower ratio of certain bacterial types
• These microbiome changes could potentially be involved in OCD, but more research is needed to determine if they play a causal role

The gut-brain connection in OCD

Obsessive-compulsive disorder (OCD) is a mental health condition characterized by intrusive, unwanted thoughts (obsessions) and repetitive behaviors or mental acts (compulsions) performed to relieve anxiety. While the exact causes of OCD are not fully understood, researchers believe it likely involves a combination of genetic, neurobiological, and environmental factors.

In recent years, scientists have become increasingly interested in the potential role of the gut microbiome - the trillions of bacteria and other microorganisms living in our digestive tract - in various psychiatric and neurological disorders. There is a known two-way communication system between the gut and the brain, referred to as the “gut-brain axis.” This means that the activity of gut bacteria can influence brain function, and conversely, psychological factors like stress can affect the composition of gut bacteria.

Some previous studies have found differences in the gut microbiomes of people with conditions like depression, autism, and ADHD compared to those without these disorders. However, very little research has looked specifically at the gut microbiome in OCD. This study aimed to explore whether people with OCD have differences in their gut and throat microbiomes compared to people without the disorder.

Examining gut and throat bacteria

The researchers collected stool and throat swab samples from 32 adults diagnosed with OCD and 32 healthy control participants matched for age and gender. They used genetic sequencing techniques to analyze the types and relative amounts of different bacteria present in these samples.

For the OCD patients, samples were collected both before starting treatment and after 3 months of treatment with medication and cognitive behavioral therapy. This allowed the researchers to see if any microbiome differences persisted after treatment.

Differences found in the gut microbiome

When examining the stool samples, a few key differences emerged between the OCD patients and healthy controls:

1. Lower bacterial diversity: The OCD patients tended to have somewhat lower diversity of bacteria in their gut microbiomes compared to the control group. While this difference was not statistically significant after adjusting for multiple comparisons, it aligns with findings from studies of other psychiatric disorders.

2. More inflammation-associated bacteria: OCD patients had higher levels of bacteria from the Rikenellaceae family, particularly the genus Alistipes. These bacteria have been associated with gut inflammation in previous research.

3. Fewer dopamine-producing bacteria: The OCD group had lower levels of bacteria from the genus Coprococcus. These bacteria are linked to the production of DOPAC, a metabolite of dopamine. Dopamine is a neurotransmitter that plays a role in reward, motivation, and movement control.

4. Other bacterial shifts: OCD patients also had lower levels of bacteria from the Prevotellaceae family and the genera Agathobacter and Lachnospira.

Interestingly, most of these differences were still present even after the OCD patients had undergone 3 months of treatment. This suggests the microbiome differences may be relatively stable features associated with OCD rather than temporary fluctuations.

Changes in the throat microbiome

The researchers also found differences when analyzing the throat swab samples:

1. Lower ratio of certain bacteria: OCD patients had a lower ratio of Fusobacteria to Actinobacteria in their throat microbiomes compared to the control group.

2. Shifts in specific bacterial groups: OCD samples showed higher levels of bacteria from the Actinobacteria and Coriobacteriia classes, including increases in the genera Actinomyces and Atopobium. They also had lower levels of bacteria from the Fusobacteriia class.

As with the gut microbiome findings, many of these throat microbiome differences persisted even after treatment for OCD.

What do these findings mean?

This study provides initial evidence that people with OCD may have distinct patterns in their gut and throat microbiomes compared to people without the disorder. However, it’s important to note that this type of study cannot prove whether these microbiome differences actually cause OCD or are simply associated with it.

The increased levels of inflammation-associated bacteria and decreased levels of dopamine-related bacteria in the gut are particularly intriguing. Some researchers have proposed that inflammation in certain brain circuits may play a role in OCD. Additionally, medications that affect dopamine signaling can sometimes help reduce OCD symptoms.

The microbiome differences in the throat are also interesting, especially given that some children develop sudden-onset OCD symptoms following strep throat infections (a condition called PANDAS). However, this study did not find evidence of increased strep bacteria in the adult OCD patients’ throat samples.

Limitations and future directions

While these findings are promising, there are some important limitations to keep in mind:

1. Small sample size: This was a relatively small, exploratory study. Larger studies are needed to confirm the results.

2. Cannot prove causation: As mentioned earlier, this type of study cannot determine whether microbiome differences cause OCD or are simply correlated with it.

3. Focus on adults: This study only included adult OCD patients. The microbiome findings may be different in children with OCD.

4. Potential confounding factors: While the researchers tried to account for factors like diet, there may be other unmeasured variables influencing the results.

Future research should aim to replicate these findings in larger groups of OCD patients. Studies that track people’s microbiomes over time, starting before they develop OCD, could help clarify whether microbiome changes precede OCD onset. Animal studies may also provide insight into whether experimentally altering the microbiome can influence OCD-like behaviors.

Conclusions

• People with OCD show differences in their gut and throat microbiomes compared to those without OCD
• These differences include increased inflammation-associated bacteria and decreased dopamine-related bacteria in the gut
• Most microbiome changes persisted even after OCD treatment
• More research is needed to determine if these microbiome differences play a causal role in OCD