Exposure in the womb, during puberty, and while pregnant is especially dangerous, researchers say.
Exposure to certain chemicals in household and industrial products is a significant risk factor for breast cancer, according to a new review, especially when the exposure occurs at an early age.
Scientists have been studying the link between breast cancer and environmental exposures—to chemicals in the air we breathe, the food we eat, and the products we use on a daily basis—for many years. In 2007, a widely cited review from the Silent Spring Institute identified 216 such chemicals that cause mammary tumors in animals, providing a roadmap for future studies in humans.
A decade later, Silent Spring scientists have published an update in the journal Environmental Research, and they say that the evidence today—including documented effects in people of all ages—is stronger than ever. They hope their report will help shape prevention strategies and increase public awareness as breast cancer rates continue to rise worldwide.
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For the new review, researchers identified and analyzed 158 studies, with human participants, published between 2006 and 2016. “We wanted to pair the human studies with what had been found in the lab and in animal studies, and see how much their findings were similar,” says lead author Kathryn Rodgers, a research scientists at Silent Spring.
In many cases, says Rodgers, they were. The researchers concluded that exposure to certain chemicals in the womb, during puberty, and through pregnancy all increase the risk of developing breast cancer later on. “During these periods, the body is changing and cells are dividing quickly, and the breasts are very sensitive and vulnerable to environmental chemicals,” says Rodgers.
For example, early-in-life exposure to air pollution, dioxin, the chemical PFOSA (used in some food packaging), and the pesticide DDT are all associated with a two- to five-fold increased risk of breast cancer, the review found.
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Workplace exposure before age 36 to solvents, textiles, and inks were associated with postmenopausal breast cancer in one study. In other research, exposure to polycyclic aromatic hydrocarbons—a chemical in vehicle exhaust—was associated with increased risk for women with certain genetic variants.
Evidence linking breast cancer and chemicals like bisphenol-A (BPA) and phthalates—found in plastics, cosmetics, and countless other store-bought items—is still limited in humans, says Rodgers. Most research in this area is relatively new, she adds, but animal studies so far have suggested a connection. These chemicals have been shown to disrupt the body’s endocrine system and hormone production, which researchers suspect may fuel cancer growth.
Despite the fact that breast cancer is the most common cancer in women worldwide, and that rates in the United States are among the world’s highest, only 5 to 10% of cases are due to inherited high-risk genes, the researchers say. Other well known risk factors include obesity, smoking, synthetic hormones, and a sedentary lifestyle.
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“We hope that physicians and nurses will start to talk to their patients about their environment—like occupational exposures, neighborhood air pollution, or hobbies or household activities—in the same way they talk to patients about smoking or diet,” says Rodgers.
People who are concerned about their risk or their children’s risk can also reduce their exposure to these chemicals by avoiding flame-retardant and stain-resistant chemicals, not microwaving food in plastic containers, and researching the chemicals in products like pesticides, cleaning products, and cosmetics, she adds. (Silent Spring also offers a free smartphone app, Detox Me, with more helpful hints.)
But ultimately, Rodgers says, better regulation and public-health policies are needed. “It shouldn’t be someone’s job when they’re going to the store to scrutinize every chemical to see if there’s something in there that can harm you,” she says. “We need stronger health protection at the state and federal level—and so voting and letting your elected officials know that you care is also something you can do.”