As many as 10 in every 100 women are believed to suffer from endometriosis, a chronic inflammatory condition in which the womb's lining starts building up in areas outside of it, too. These extrauterine endometriosis lesions can affect many different parts of the reproductive system and beyond — the fallopian tubes, ovaries, bladder, and bowels, for instance. Unsurprisingly, persistent pelvic pain is one of the main symptoms.
Inflammation is a crucial factor that causes pain and other symptoms in these conditions, which include:
- Chronic fatigue syndrome
- Rheumatoid arthritis
- Irritable bowel disease
- Celiac disease
What does endometriosis have to do with the thyroid?
The thyroid is an important gland in the neck that is responsible for producing hormones that help regulate metabolism as well as growth and body temperature. Estrogen metabolism (may further contribute to the development of thyroid nodules) and inflammation both play large roles in endometriosis, and patients have proinflammatory cytokines (proteins needed for cell signaling). These proinflammatory cytokines are likewise linked to two autoimmune thyroid conditions:
- Hashimoto’s Thyroiditis
- Graves’ Disease
What should you know about the connection between endometriosis and Hashimoto's thyroiditis?
Hashimoto's thyroiditis, an autoimmune condition that leads to chronic inflammation, is the number one cause of hypothyroidism (an underactive thyroid) in the US. Symptoms include unexplained weight gain, fatigue, infertility and irregular, heavy, periods (also common in endometriosis), muscle pain, joint pain, hair loss, and constipation.
A large study of women with surgically-confirmed endometriosis demonstrated that many patients also suffer from autoimmune conditions, with Hashimoto's thyroiditis being 6.5 times more common in endometriosis patients. Both conditions have been linked to Th1 cell-associated cytokines.
What is the link between endometriosis and Graves' disease?
Graves' disease is another autoimmune condition — but in this case, antibodies (thyroid-stimulating immunoglobulins or TRIs) cause the thyroid gland to become overactive. Goiter, vision problems, gastrointestinal issues, weight loss, and muscle weakness are some of its symptoms. Research suggests that there is a correlation between the two, a conclusion that was reached after controlling for other variables. This study wasn't able to confirm a higher rate of hypothyroidism, autoimmune or otherwise, however.
What is the possible reason for the correlation between endometriosis and Graves' Disease? There are two, actually:
- Autoimmunity. Inflammation and polyclonal B cell activation are just two features endometriosis shares with autoimmune conditions, and patients also have a higher number of positive antinuclear antibodies, thyroid peroxidase antibody, and other antibodies — just like people with Graves' Disease do.
- Estrogen. You already know that endometriosis is estrogen-dependent, but did you know this female hormone also plays a role in the development of Graves' Disease? Estrogen contributes to its development by change the way in which the immune system responds, and this may explain why women are diagnosed with Graves' Disease at higher rates.
What does this mean for the link between endometriosis, thyroid autoimmune conditions, and thyroid dysfunction?
Scientists want to know too — which is why the possible link between endometriosis and thyroid dysfunction, including thyroid autoimmune diseases, has been studied quite extensively. A consensus has not yet been reached, but various studies have found that:
- Endometriosis patients appear to have a higher risk of developing autoimmune disorders, including thyroid autoimmune conditions, so one study compared the rates of thyroid dysfunction and autoimmune thyroid disorders in endometriosis sufferers to those in a group of women without endometriosis. Looking at their levels of thyroid-stimulating hormone and various antibodies, they didn't find that endometriosis patients have higher rates of thyroid problems and did not feel they could advise that women with endometriosis should be routinely screened for them. The study sample was small, however.
- Other research found that women with endometriosis who suffered from infertility as a result of ovarian failure had a markedly higher risk of also being diagnosed with a thyroid autoimmune condition.
- Further studies demonstrated a correlation between endometriosis and thyroid autoimmune disease, concluding that participating women with a thyroid autoimmune disease had much higher rates of endometriosis.