Dioxin exposure through the food chain during pregnancy could explain why some women have trouble breastfeeding or produce too little milk, new research suggests.

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.

New findings

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. 

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