Researchers discovered that people with endometriosis have higher levels of a brain chemical called serotonin in their reproductive organs and gut. This serotonin appears to come from specific bacteria that live in both the gut and reproductive tract, and it may be making endometriosis worse by causing more cell growth and inflammation. Scientists studied tissue samples from 22 endometriosis patients and 22 control patients, then tested their findings in mice and lab cells. This discovery could lead to new ways to treat endometriosis by targeting these bacteria or serotonin levels.
The Quick Take
- What they studied: Whether a brain chemical called serotonin, produced by gut bacteria, plays a role in causing endometriosis (a painful condition where tissue grows outside the uterus)
- Who participated: 22 women with endometriosis and 22 women with uterine fibroids (used as a comparison group) who had surgery between October 2022 and June 2023, plus additional blood samples from 20 more endometriosis patients and 20 healthy women
- Key finding: Women with endometriosis had significantly higher serotonin levels in their blood and reproductive tissues compared to control groups. A specific gut bacteria called Akkermansia muciniphila was more common in endometriosis patients and was linked to higher serotonin levels
- What it means for you: This research suggests that endometriosis may be partly caused by an imbalance in gut bacteria that produces too much serotonin. This could eventually lead to new treatments targeting bacteria or serotonin levels, though much more research is needed before any changes to treatment
The Research Details
This was a cross-sectional study, which means researchers collected samples from two groups of people at one point in time and compared them. The study collected multiple types of samples from each participant: vaginal secretions, tissue from the uterus, fluid from the abdominal cavity, stool samples, and blood. They analyzed the bacteria in these samples using genetic testing and looked for chemical markers like serotonin.
The researchers used several advanced techniques to understand their findings. They identified which bacteria were present using genetic sequencing (like reading a bacterial fingerprint). They measured serotonin levels in blood using a standard lab test. They also grew endometriosis cells in the lab and exposed them to serotonin to see what happened. Finally, they tested their findings in mice to see if serotonin actually caused endometriosis to worsen.
This multi-layered approach—combining bacteria analysis, chemical detection, cell studies, and animal testing—allowed the researchers to build a stronger case that serotonin from gut bacteria may be involved in endometriosis.
Understanding how endometriosis develops is crucial because it affects millions of women and causes severe pain and infertility. Previous research showed that serotonin can worsen other inflammatory diseases, but no one had carefully studied whether it plays a role in endometriosis. By examining the connection between gut bacteria, serotonin, and endometriosis across multiple body locations, this study provides a more complete picture of how the disease might develop. This could lead to entirely new treatment approaches.
Strengths: The study used multiple research methods (genetic analysis, chemical testing, cell studies, and animal models) which strengthens confidence in the findings. The researchers validated their findings in additional patient samples and mouse models. The study was published in a reputable journal (Human Reproduction). Limitations: The sample size was relatively small (only 22 endometriosis patients), which means results may not apply to all women with endometriosis. The control group consisted of women with uterine fibroids rather than completely healthy women, which could affect comparisons. The study didn’t measure hormone levels or collect dietary information, both of which could influence the results. The study shows associations but doesn’t prove that bacteria directly cause the serotonin increase.
What the Results Show
The study found that women with endometriosis had significantly higher serotonin levels in their blood compared to healthy women and women with uterine fibroids. When researchers examined tissue from the reproductive organs, they found elevated serotonin in the abnormal endometriosis lesions compared to normal uterine tissue.
A specific type of bacteria called Akkermansia muciniphila was much more abundant in endometriosis patients. Importantly, this bacteria was found in both the gut and the reproductive tract of these patients, suggesting a connection between these two body systems. The amount of this bacteria was directly linked to serotonin levels—more bacteria meant more serotonin.
When researchers exposed endometriosis cells to serotonin in the laboratory, the cells became more aggressive. They grew faster, moved more easily, invaded surrounding tissue more readily, and were less likely to die naturally. The serotonin activated inflammatory pathways in the cells, meaning it triggered the body’s inflammatory response.
In mice treated with serotonin, endometriosis lesions grew larger and more severe, with increased inflammation and cell growth, mirroring what happens in human patients.
The study found that serotonin activated specific inflammatory pathways (IL-17/NF-κB) in endometriosis cells, which are known to drive inflammation and cell growth. This explains one mechanism by which serotonin makes endometriosis worse. The research also showed that the connection between bacteria and serotonin appears to work through the gut-reproductive axis—a communication system between the digestive tract and reproductive organs. This suggests that treating the gut microbiota might influence reproductive health.
Previous research had shown that serotonin can worsen other inflammatory diseases like irritable bowel syndrome and certain cancers. This study is the first to systematically examine serotonin’s role in endometriosis and to connect it to specific gut bacteria. The finding that gut bacteria influence reproductive health through serotonin production is relatively new and expands our understanding of how the gut microbiota affects distant body systems.
The study had several important limitations that readers should understand. First, only 22 endometriosis patients were studied, which is a small number that may not represent all women with endometriosis. Second, the comparison group had uterine fibroids rather than being completely healthy, which could affect how different the groups really are. Third, the researchers didn’t measure sex hormone levels, even though hormones are known to be important in endometriosis. Fourth, they didn’t ask about diet, which significantly affects gut bacteria composition. Fifth, while the study shows that Akkermansia muciniphila is associated with higher serotonin and endometriosis, it doesn’t prove that the bacteria directly causes the serotonin increase—more research is needed to establish this causal relationship. Finally, the study was conducted in a specific geographic region during a limited time period, which may affect how well the findings apply to other populations.
The Bottom Line
Based on this research, there are no immediate treatment changes to recommend, as this is early-stage research. However, the findings suggest that future treatments might target gut bacteria or serotonin levels to help endometriosis. If you have endometriosis, continue working with your healthcare provider on current treatment options. Maintaining a healthy gut microbiota through diet and lifestyle may be beneficial, though this study didn’t directly test dietary interventions. Confidence level: Low to Moderate—this is promising research but requires validation in larger studies before clinical recommendations can be made.
This research is most relevant to women with endometriosis or those at risk for developing it. It may also interest women with other inflammatory conditions linked to gut health. Healthcare providers treating endometriosis should be aware of these findings as they may inform future treatment development. Women without endometriosis don’t need to make changes based on this single study. People with other conditions influenced by serotonin (like depression or IBS) may find this research interesting but shouldn’t change their treatment without consulting their doctor.
This research is in early stages. Even if treatments targeting bacteria or serotonin are developed based on these findings, it typically takes 5-10 years for new treatments to move from laboratory research to clinical use. Don’t expect immediate changes to endometriosis treatment, but this research opens promising new directions for future therapies.
Want to Apply This Research?
- Track endometriosis symptom severity (pain level 1-10, bleeding intensity, daily functioning impact) weekly alongside dietary patterns and digestive symptoms to identify personal correlations between gut health and reproductive symptoms
- Users could log daily dietary choices and gut health indicators (bloating, digestion quality, bowel regularity) to build awareness of how diet affects their symptoms, then experiment with gut-friendly foods (fiber-rich, fermented foods) while tracking symptom changes
- Establish a baseline of current symptoms and gut health over 2-4 weeks, then implement dietary modifications for 8-12 weeks while consistently tracking both reproductive and digestive symptoms to identify personal patterns and share data with healthcare providers
This research is preliminary and has not yet led to approved treatments for endometriosis. The findings are based on a small study and require validation in larger populations before clinical recommendations can be made. If you have endometriosis, continue working with your healthcare provider on established treatment options. Do not change your current treatment based on this research alone. This article is for educational purposes and should not be considered medical advice. Always consult with a qualified healthcare provider before making changes to your health regimen.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.