Fact Sheets

Endometriosis

Issue: Environmental chemicals may play a role in the development and progression of endometriosis.

Background: Endometriosis is an estrogen dependent disease in which cells that line the uterus (endometrial cells) begin to grow in the pelvis and abdomen, most commonly on the ovaries, the outer surface of the uterus, the intestines or the ligaments that support the uterus. It is estimated that this disease affects approximately 15 % of women of reproductive ages. Women with endometriosis experience pain on menstruation and intercourse often leading to time off work, medication and in many cases surgery. The cause of endometriosis remains undetermined.

Disease trends: There is very little known concerning changes in the frequency of this disease. For example, it is not known if there are more women with endometriosis today than in previous years. In addition, it is not known if women living in regions with high exposure to environmental chemicals are at greater risk for developing this disease.

Consistency of the data: A small number of hospital-based studies have been conducted in which the association between endometriosis and exposure to polychlorinated biphenyls (PCBs) and dioxin (TCDD) have been investigated. While two studies have reported a positive association between exposure to these chemicals and endometriosis the other two studies were unable to find a relationship. Unfortunately the number of patients included in theses studies was too small to generate convincing evidence either in support of or against an association between endometriosis and environmental chemicals.

Experimental evidence: In rhesus monkeys long term exposure to TCDD in the diet has been shown to be associated with an increased frequency and severity of spontaneous endometriosis. Analysis of the serum from these monkeys revealed an association between endometriosis and exposure to TCDD and PCBs that act through the same receptor as TCDD. However, a second rhesus monkey study with long-term exposure to a commercial PCB mixture failed to find any relationship between this mixture of chemicals and endometriosis. A third study involving Cynomolgus monkeys showed that dioxin treatment at low doses antagonized the growth of endometrial cells whereas higher doses increased the survival and growth of these cells.
In both rats and mice environmental chemicals such as the pesticide methoxychlor as well as PCBs and TCDD have been shown to facilitate the survival and growth of endometrial cells. These studies show that estrogenic chemicals can act to promote the growth of endometrial cells placed in the abdomen of these animals. A recent study has demonstrated that TCDD can antagonize the growth inhibiting effects of progesterone on endometrial cells growing outside of the uterus.

Biological plausibility: While both the human and animal data are inconclusive, the animal data show that environmental chemicals can affect the growth of endometrial cells albeit at high concentrations compared to the levels measured in tissues of the general population. However, it is not known if these chemicals are acting like hormones or are antagonizing the effects of the body's hormones through non-endocrine mechanisms.

Conclusion: Taken together the data do not support a conclusion that environmental chemicals are playing a role in the development or progression of endometriosis. The evidence does support however a conclusion that environmental chemicals may play a role in the pathology of this disease.