Is There a Link Between Endometriosis and the Vaginal Microbiome?

Little is known about whether or not there is a link between endometriosis and the vaginal microbiome. Still, one thing is certain: they’re two severely misunderstood and under-researched — albeit emerging — topics. 

Because endometriosis has been traditionally considered a disease of the female reproductive tract, you can blame the gender health gap for this lack of research. But is there a relationship between the vaginal microbiome and endometriosis? Research has begun to determine if there could be a link, but we still don’t have definitive answers. 

Below, we take a comprehensive look at endometriosis and then how the vaginal microbiome may be linked.

What is endometriosis?

Endometriosis is a chronic disease that happens when tissue similar to the lining of the uterus (endometrium) grows outside the uterus, such as the ovaries and fallopian tubes.

Although this tissue has some similarities with the lining of the uterus, it's not just a uterine or menstrual disease. It often appears as lesions, called implants, throughout the body and can affect nearly all organ systems. While it's commonly found in the pelvis and reproductive organs, it can also be found outside the pelvic cavity, which is known as extrapelvic endometriosis. Endometriosis can lead to adhesions, fibrosis, scar tissue and organ dysfunction due to its association with an inflammatory process.

It's estimated that around 10% of women and people with vaginas may have endometriosis, but the exact number is hard to tell due to the challenges involved in diagnosis. It's important to note that endometriosis can occur in fetuses, adolescents who haven't had their first period yet, people of reproductive age, and post-menopausal people. Interestingly, endometriosis has been documented in 17 cases in males.

Is there a link between the vaginal microbiome and endometriosis?

The vaginal microbiome is linked with many gynecological conditions, from chronic vaginal infections and your risk of getting an STI, to infertility and vaginal atrophy. So, could the systemic inflammatory nature of endometriosis cause the vaginal microbiome to be altered?

A recent review investigated the potential relationship between the microbiome and endometriosis, infertility, and chronic pelvic pain in 28 studies. The review determined that the available data and the methods from each study varied too much to make a solid conclusion but called for better quality research to further our understanding of the possible connection.

A separate systematic review compared seven different endometriosis microbiome studies. It found that the studies varied widely in how they sampled the microbiome (vagina, cervix, or endometrium), how many patients were included, how they diagnosed endometriosis, and the bacteria found. 

For example, one study found that there were no differences in microbiomes between the endometrium and vaginal samples in patients with and without endometriosis. Yet, in that same study, they found a difference in samples from deeply infiltrating endometriosis lesions compared to controls. However, the sample sizes were too small to draw conclusions. 

‍Some studies found that Atopobium was more frequently detected in the vagina of endometriosis patients, while other studies found it more frequently in patients without. In yet another study, Fusobacterium is implicated. But as we often say, correlation doesn’t mean causation, so we don’t yet know if these bacteria contribute to symptoms or are the result of symptoms and treatment involved in endometriosis.

Unfortunately, it’s hard to draw conclusions from the studies that have been done for several reasons. In most studies, the control population was made up of patients going in for “benign gynecological surgeries.” This is problematic because the reason for these surgeries is varied, so it’s hard to determine if the people studied are  representative of people not included in the study. Finally, most of the studies had a very small sample size (this means that the number of people in the study was small, so it’s difficult to know if the results are meaningful).

Lactobacillus is one of the most important bacteria studied when investigating the health of the vaginal microbiome. Lactobacilli are the good, protective bacteria necessary for maintaining a healthy environment by keeping the vaginal pH right where it needs to be. Lactobacilli rely on estrogen to survive and keep vaginal tissue healthy!

Therefore, the inflammatory nature and hormone fluctuations (including changing estrogen levels) associated with endometriosis and its treatments, could have an impact on the vaginal microbiome. We just don’t fully understand how this interaction plays out. So far, several studies found that Lactobacillus was the most common organism in both endometriosis and control patients (Chen 2020, Ata 2019, Akiyama 2019, Hernandes 2020, Chao 2021, Perrotta 2020). 

While endometriosis itself may or may not be associated with the vaginal microbiome, many of the treatment options discussed earlier directly affect it. To the best of our knowledge, no one has studied the impact endometriosis treatments have on the vaginal microbiome. This can leave endometriosis patients confused and looking for more answers if they have symptoms associated with a disrupted vaginal microbiome. 

Because the goal of hormone therapies for endometriosis is to reduce levels of estrogen, a dramatic drop in estrogen can deplete the vagina from Lactobacillus! This leads to what is known as genitourinary syndrome of menopause, previously called vulvovaginal atrophy.  Most commonly, stronger medications that induce medical menopause, such as the GnRH Agonists and GnRH Antagonists can cause vaginal symptoms and infections. 

These symptoms include, but are not limited to: 

• Vaginal dryness
• Vulvovaginal Irritation/burning/itching
• Dyspareunia (painful sex)
• Recurrent urinary tract infections
• Yeast infections
• Bacterial infections

These symptoms often get overlooked or blamed on something other than the lack of vaginal estrogen and a disrupted vaginal microbiome. Fortunately, vaginal testing can be an effective method for determining if a lack of estrogen could be the culprit. With this information, a proper treatment plan can be made. 

It’s possible that the vaginal microbiome is connected to endometriosis, like whether or not endometriosis itself causes an altered microbiome, but we just don’t have reliable research yet! Until then, it is important to monitor and treat vaginal symptoms that may be associated with medications commonly used for those with endometriosis, and this is where Evvy can help.