What Causes Endometriosis?
Endometriosis is a complex and often misunderstood condition where tissue resembling the endometrium—the lining inside the uterus—begins to grow outside of it. These abnormal growths, known as lesions, can appear in various parts of the body, though they are most commonly found on reproductive organs, the colon, and the bladder. Despite ongoing research, the exact cause of endometriosis remains elusive. However, experts have proposed several theories, each pointing to an intricate interplay of genetic, environmental, and lifestyle factors that may contribute to its development.
Theories Behind Endometriosis
The mystery of endometriosis has led researchers to explore a variety of theories, each offering a unique perspective on how and why this condition arises. While no single theory provides a definitive answer, they collectively highlight the multifaceted nature of the disease.
Retrograde Menstruation
One of the earliest theories, proposed by gynecologist John Sampson in 1927, is retrograde menstruation. This theory suggests that during menstruation, instead of exiting the body through the vagina, some menstrual blood flows backward into the fallopian tubes. From there, it spreads into the pelvic cavity, carrying endometrial cells that implant and grow outside the uterus.
However, this theory has lost some of its initial support. Why? Because endometriosis has been found in individuals who do not menstruate, including cisgender men and fetuses. This discovery has led researchers to question whether retrograde menstruation is the sole—or even primary—cause of the condition.
Coelomic Metaplasia
Metaplasia refers to the process where one type of cell transforms into another. In the case of coelomic metaplasia, cells outside the uterus are thought to undergo this transformation, turning into endometrial-like cells. These cells then grow and form lesions on nearby organs.
Some researchers believe that factors like retrograde menstruation, hormonal imbalances, or a compromised immune system could trigger this cellular transformation. While intriguing, this theory is still under investigation, and its exact role in endometriosis remains unclear.
Vascular and Lymphatic Metastasis
Endometriosis doesn’t always confine itself to the pelvic region. In rare cases, endometrial-like cells have been found in distant organs, such as the lungs. To explain this phenomenon, Sampson proposed the theory of vascular and lymphatic metastasis.
The vascular aspect of this theory suggests that tiny blood vessels, or capillaries, can transport endometrial cells to far-off parts of the body. Meanwhile, the lymphatic aspect posits that these cells might travel through the lymphatic system—a network of vessels and nodes that help filter harmful substances. This theory could explain how endometriosis can appear in unexpected places, though it remains a rare occurrence.
Stem Cells
Stem cells are the body’s ultimate repair crew, capable of developing into various cell types to heal and regenerate tissues. In the uterus, stem cells help rebuild the endometrium after menstruation. However, some researchers believe that these stem cells might migrate outside the uterus, where they develop into endometrial-like cells and form lesions.
This theory offers a compelling explanation for how endometriosis can persist and recur, even after treatment. Stem cells’ regenerative nature might contribute to the condition’s chronic and often relentless progression.
Embryonic Cells
During fetal development, embryonic stem cells differentiate into specialized cells that form various organs and tissues. However, some cells might remain “residual,” failing to fully specialize. These leftover cells could later develop into endometrial-like cells under the influence of estrogen, even before menstruation begins.
This theory might explain why endometriosis can occur in individuals who have not yet started their periods, including young adolescents and even fetuses. It underscores the potential role of early developmental factors in the condition’s onset.
Hormone Imbalances
Estrogen, a key hormone in the menstrual cycle, plays a significant role in endometriosis. High levels of estrogen can exacerbate symptoms, leading to severe pain, inflammation, and lesion growth. Hormonal imbalances, particularly those involving estrogen and progesterone, are thought to contribute to the development and progression of the condition.
For instance, individuals with endometriosis often experience more pain and symptom flares when their estrogen levels are elevated. This connection has led to treatments aimed at suppressing estrogen to manage symptoms.
Surgery
While less common, some studies suggest that endometriosis might develop as a result of surgical procedures, such as Cesarean sections (C-sections) or hysterectomies. During these surgeries, endometrial tissue could inadvertently be transferred outside the uterus, where it implants and grows. However, this theory requires further research to establish a definitive link.
Is Endometriosis Hereditary?
Genetics may also play a role in endometriosis. Individuals with a close family member, such as a mother or sister, who has the condition are at a higher risk of developing it themselves. Researchers have identified several genes associated with endometriosis, including:
- VEZT: A gene involved in embryo implantation, which, when mutated, may increase the risk of endometriosis.
- NPSR1: Linked to inflammation in the uterus.
- WNT4: Associated with abnormal cell growth in reproductive organs.
- FN1/GREB1: Influences estrogen production, potentially contributing to hormonal imbalances.
While genetic testing for endometriosis is not yet available, ongoing research aims to uncover how these genetic mutations contribute to the condition and whether they can be targeted for treatment.
Who Gets Endometriosis?
Endometriosis primarily affects individuals who menstruate, but certain factors can increase the likelihood of developing the condition. These include:
- Early onset of menstruation (before age 11).
- Short menstrual cycles (less than 27 days).
- Heavy or prolonged periods lasting more than seven days.
- Spotting between periods.
Risk Factors
Beyond biological factors, several risk factors have been identified:
- Weight: The relationship between body mass index (BMI) and endometriosis is complex. Some studies suggest a low BMI increases risk, while others point to obesity as a potential factor.
- Age: Endometriosis is most commonly diagnosed in individuals between 15 and 40, the typical reproductive age range.
- Pregnancy: Those who have never been pregnant may have higher estrogen levels, potentially increasing their risk.
- Lifestyle: Factors such as limited physical activity (less than three hours of exercise per week) and excessive alcohol consumption (more than one drink per day) may also play a role.