Environmental toxins and endometriosis

Several studies have suggested that exposure to persistent pollutant, polychlorinated biphenyls (PCBs), may increase the risk of developing endometriosis

Key Points

Highlights:

• Although the role of polychlorinated biphenyls (PCBs) in the development of endometriosis is uncertain, increasing evidence shows a relationship between PCBs and endometriosis.

Importance:

• PCBs are manufactured globally and used widely in electrical industry. However, due to their high stability, they do not biodegrade, resulting in the contamination of the environment (e.g., rivers, buildings, parks, etc.) as well as the food supply.  
• PCB production was banned by the United States Congress in 1979. The International Agency for Research on Cancer (IARC) categorized PCBs as carcinogens in humans in 2012.
• Exposure to PCBs may cause endocrine disruption; PCBs may enhance the effect of estrogen, leading to increased incidence of estrogen-dependent cancers and possibly endometriosis.

What’s done here?

• This is a review article summarizing and discussing the potential impact of PCB exposure on endometriosis.

Key results:

• The association between PCBs and endometriosis is controversial. Some studies found an increased incidence of endometriosis in women exposed to moderate to high PCB, while others found no link between serum levels of PCBs and endometriosis.

Limitations of the study:

• There were many discrepancies among the previous controversial studies summarized in this review article:

• Many studies followed different study protocols. Any meaningful comparison of analytical results requires standardization of research protocols such as serum collection procedures; dietary habits, age, body weight, blood lipids, and pregnancy history of human subjects; environment, etc.
• Different PCB assessment methods were utilized by different studies, which may lead to miss-detection of PCBs and false-negative results, especially when considering there are 209 possible congeners in PCB family.
• Identification of endometriosis can be difficult; the gold standard for the diagnosis is a laparoscopic inspection. However, the sensitivity and specificity of detection vary widely among surgeons.
• Different types of endometriosis (peritoneal, ovarian, and deep infiltrating) may differ in their pathogenesis.

Lay Summary

Polychlorinated biphenyls (PCBs) are organic chlorine contaminants that were widely used in industry due to their excellent physicochemical properties. However, they were banned in the US and the rest of the world in 1979. PCBs are highly stable and resistant to environmental degradation. Thus, they persist in both the environment and body. PCBs are fat-soluble and may concentrate in the human body through the food chain.

This review article from by Yao M et al., from Zhejiang University, China, published in the scientific journal Environmental Pollution discussed the potential pathophysiological relationship between endometriosis and PCBs with a focus on both dioxin-like and non-dioxin-like PCBs.  Several population-based studies have suggested that exposure to PCBs may increase the risk of developing endometriosis. These studies stem from previous recognition of a relationship between endometriosis and dioxin – an environmental pollutant structurally similar to PCBs. Exposure to PCBs was found to enhance the effects of estrogen, leading to increased incidence of estrogen-dependent cancers and possibly endometriosis. PCBs may disrupt the endocrine system by binding to estrogen and producing estrogenic effects. Therefore, it is plausible to suspect PCBs involvement in the onset and development of estrogen-dependent clinical conditions such as endometriosis.

While many have investigated the relationship between endometriosis and PCBs, results were conflicting, primarily due to variations (1) in study protocols – PCBs are highly soluble in fat, therefore, dietary habits, age, weight, and blood lipids of participating patients matter when generalizing the findings; and (2) in PCB analysis methods used - there is 209 varieties of PCBs, thus, the detection of PCBs highly depend on the use of advanced technology to assess them accurately. Unless, the study protocols and analysis methods are standardized, it is inevitable to end up with controversial results. Another point to consider is the difficulty and variability in endometriosis diagnosis, and the possibility that different types of endometriosis (peritoneal, ovarian, and deep infiltrating) may not share the same manner of disease development. Future studies should focus on the type of endometriosis and their particular relationship to PCBs.

Research Source: https://www.ncbi.nlm.nih.gov/pubmed/28774553