A study from the University of Rochester Medical Center (URMC), in the United States, has found that contact with the toxic chemical harms the cells in rapidly changing breast tissue that occurs during pregnancy.
While the results have only been demonstrated in mice so far, researchers believe their investigations may help to address an issue that affects between three and six million women worldwide.
Role of environmental contaminants
B. Paige Lawrence, Ph.D., associate professor of Environment Medicine and of Microbiology and Immunology at URMC, said: “The cause of this problem is unclear, though it has been suggested that environmental contaminants might play a role. We showed definitively that a known and abundant pollutant has an adverse effect on the way mammary glands develop during pregnancy."
The group said that most people are exposed to dioxins through diet. The majority of dioxins are generated by the incineration of municipal and medical waste – especially certain plastics – and these enter the food chain when air emissions settle on food crops and pastures where livestock graze.
Humans are said to ingest dioxins mostly through eating meat, dairy products and shellfish. The chemical settles in the fatty tissues where “natural elimination occurs very slowly”, said the URMC reseachers. The typical daily exposure is thought to be low but this has already been linked to health problems such as possible impairment of the immune system and developing organs, added a statement from the group.
In 2004, Lawrence’s laboratory discovered that dioxin hampers the normal development of mammary glands during pregnancy – but factors such as the underlying mechanisms for this and when exposure during pregnancy was most significant remained unclear.
However, findings reported in Toxicological Sciences this week demonstrated that dioxin “has a profound effect on breast tissue by causing mammary cells to stop their natural cycle of proliferation as early as six days into pregnancy, and lasting through mid-pregnancy”, said Lawrence. Tissue samples taken from mice showed a 50 percent decrease in new epithelial cells that help to protect or enclose organs, she added.
This is significant, said Lawrence, because mammary glands have a high rate of cell proliferation, especially during early to mid-pregnancy when their most rapid development occurs. Researchers also found that dioxin causes other problems with the breast such as altering the induction of milk-producing genes, which occurs around the ninth day of pregnancy.
Timing irrelevant for humans
The timing of dioxin exposure also seemed to be significant, the study noted. Results showed early exposure may give time for the cells to recover. But Lawrence stressed that while understanding of the timing of exposure was important for reseach purposes it was “irrelevant for humans, who cannot really control their exposure to dioxins".
She added: “Our goal is not to find a safe window of exposure for humans, but to better understand how dioxins affect our health. We hope this study raises awareness about how our food sources can increase the burden of pollutants in the body.”