Our Stolen Futurea book by Theo Colborn, Dianne Dumanoski, and John Peterson Myers
 
 

 

 

Rier, S and WG Foster. 2002. Environmental dioxins and endometriosis. Toxicological Sciences 70:161-170.


Rier and Foster review evidence from animal and human studies indicating that dioxin (and other dioxin-like compounds) causes endometriosis via its ability to disrupt immune and endocrine system function. They conclude that existing data support this interpretation but that the details of the mechanisms are not yet clear.

They also show that human exposure to dioxin is significantly higher than that associated with endometriosis in monkeys., and cite published work which concludes that current public health standards are not strong enough to provide guarantees against the potential for dioxin causing endometriosis.

What does this mean? Dioxins are highly likely to be involved in the causation of endometriosis. Many people carry dioxin body burdens that animal experiments predict should cause endometriosis. The disease itself has likely increased dramatically in prevalence over the past century, the same period over which human dioxin body burdens grew. In the US alone, endometriosis forces over 100,000 hysterectomies each year, with health care costs for the disease exceeding $1 billion annually. Strong measures to reduce dioxin exposures are warranted.

Key parts of their review:

A summary of the action of dioxin and dioxin-like compounds:

 
  • This group of chemicals, the polyhalogenated aromatic hydrocarbons (PHAHs), includes not just dioxins (PCDDs) but also furans (PDDFs) and biphenyls (PCBs).
  • PHAH compounds bind with the aryl hydrocarbon receptor (AhR), migrate to the nucleus and activate genes, including several involved in controlling cell growth, differentiation and inflammation.
  • Evidence demonstrates that different dioxins can act additively via this mechanism. To assess the effects of dioxin mixtures, scientists have developed a dioxin "toxic equivalency factor" (TEF) based upon the relative potency of different congeners compared to TCDD(2,3,7,8-tetrachlorodibenzo-p-dioxin) the most potent of the compounds, and then used the summed TEFs to calculate the total TCDD equivalency (TEQ).
  • Most human exposure to dioxin comes via food. "In developed countries, blood levels typically run 1-5 parts per trillion TCDD and 25 ppt TEQ, at least for people without industrial exposure.
  • "Although the toxic effects of TCDD in animals are unequivocal, its effects in humans are less clear."

A review of data on dioxin-endometriosis links in monkeys:

 
  • The first hard data linking endometriosis and dioxin came from Rier et al.'s 1993 work with rhesus monkeys. They discovered, 10 years after TCDD exposure was ended, that exposed monkeys had developed endometriosis: the more dioxin, the greater the incidence and severity of the disease. Exposures were in the low parts per trillion.
  • Subsequent studies with monkeys have strengthened this conclusion. For example, a study of cynomolgus monkeys found that TCDD exposure increased the implantation rate of endometrial tissue.
  • And in 2001, Rier et al. published additional work with rhesus monkeys showing that higher TEQ levels were associated with a higher prevalence of endometriosis. Disease severity was positively related to PCB congeners, but not to TCDD itself. In this study, the animals were exposed to PHAH compounds through food, as are people.

Comparison of exposures of people to those of the monkeys in these experiments:

 
  • Their comparison reveals that the body burdens in people living in the real world are 2 to 20-fold higher than the monkeys in the experiments.
 
  • Rier and Foster cite a Japanese calculation that "protection against development of endometriosis cannot be guaranteed by current regulatory safeguards, since exposure to dioxin and dioxin-like compounds in certain at-risk populations, such as local residents living near incinerators or who are heavy fish consumers are greater than the levels for which adverse effects have been documented in rhesus monkeys."

It would thus seem that if human endometriosis has a comparable dose response relationship to that revealed by the experiments with monkeys, then it is not surprising that endometriosis is as widespread in people as data currently indicate.

Evaluation of the value of animal models for understanding human endometriosis:

 
  • Only menstruating species like people and monkeys develop endometriosis. Rhesus endometriosis closely resembles the human form.
  • Surgical transplantation of endometrial tissues in other species, such as rodents, can be used to study the factors that affect the chances that the tissue will thrive in other locations, but not of the the earliest stages of development of endometriosis.
  • New approaches are being developed that transplant endometrial tissues into immune-deficient mice. The implants resemble endometrial lesions in people. This may allow more cost-effective and rapid research than studies with monkeys.

Human studies on dioxin and endometriosis:

 
  • Four hospital based case-control studies have been published. Results are mixed. None of the studies are ideal, all with small sample sizes. Two (both negative) failed to confirm surgically that the control population did not have endometriosis. A third negative study used a chemical assay that probably underestimated TEQ. The one positive study found that infertile women with endometriosis were more likely to have detectable levels of TCDD than fertile women without endometriosis.

Potential mechanisms by which dioxin could cause endometriosis:

 
  • Rier and Foster begin this section summarizing studies showing that the dioxin stimulates gene activation in endometrial tissue through binding with the Ah receptor.
  • They then propose that this gene activation may promote endometriosis through three pathways:
 

First, by inducing an enzyme that increases estrogen levels and results in "chronic exposure of the endometrium to growth-promoting estrogen."

Second, by stimulating certain cytokines (immune system proteins) involved in immune system responses and in the regulation of cycles of cell division and death, thereby inducing inflammation and immune dysfunction.

Third, by interfering with progesterone. This hormone normally helps block formation of endometrial lesions.

They conclude: "Although preliminary work suggests a potential involvement of exposure to dioxins in the pathogenesis of endometriosis, much work remains to clearly define cause and effect and to understand the potential mechanism of toxicity."

 

 
     
     

 

 

 

OSF Home
 About this website
Newest
Book Basics
  Synopsis & excerpts
  The bottom line
  Key points
  The big challenge
  Chemicals implicated
  The controversy
  Recommendations
New Science
  Broad trends
  Basic mechanisms
  Brain & behavior
  Disease resistance
  Human impacts
  Low dose effects
  Mixtures and synergy
  Ubiquity of exposure
  Natural vs. synthetic
  New exposures
  Reproduction
  Wildlife impacts
Recent Important    Results
Consensus
News/Opinion
Myths vs. Reality
Useful Links
Important Events
Important Books
Other Sources
Other Languages
About the Authors
 
Talk to us: email