Exposure to bisphenol A (BPA), an endocrine disruptor, might be associated with increased risk of breast cancer. BPA that has leached from food packaging and containers is the main source of exposure. BPA has been shown to induce breast cancer cell proliferation. Chronic low-level BPA exposure during adulthood increases tumor development in mice. BPA also induces mammary cell proliferation in BRCA1-deficient mice, leading to hyperplasia. Finally, BPA can reduce the effectiveness of some types of chemotherapy. Taking reasonable steps to limit exposure to bisphenol A makes sense.
Food packaging and containers are the main sources of bisphenol A exposure
Exposure to BPA is widespread. BPA is one of the highest-volume chemicals produced worldwide; it can be detected in the body fluids of over 90% of the human population. BPA is used extensively in the production of consumer goods, polycarbonate plastics, and epoxy resins. BPA is present in canned food and canned soda as a result of leaching from interior epoxy coatings used to prevent corrosion. BPA also migrates into water stored in polycarbonate plastic bottles and some lined reusable metallic water bottles. Heat increases the leaching of BPA from food and beverage containers.
In addition, BPA is found in consumer products made from polycarbonate plastics, such as baby bottles, sports equipment, eyeglass lenses, compact discs and implantable medical devices. BPA is also a component of the resins used in some plastic water pipes, dental sealants and paints. Furthermore, BPA has been found in or on a wide variety of papers and cardboards, including cash register receipts, papers used for wrapping food, cigarette filters and U.S. paper currency.
It has been demonstrated that BPA exposure from canned and packaged food can be significant. One study had healthy volunteers consume a 12-ounce serving of freshly made soup (prepared without any canned ingredients) for five days, followed by a two-day washout period, then five days of consuming a serving of canned Progresso soup. Urinary levels of BPA increased nearly 20-fold as a result of eating the canned soup, but the increases were not persistent. It is unknown how such short-term elevations in BPA levels affect human health.
Bisphenol-S (BPS) is now used as a bisphenol-A substitute and has been described as safer than BPA. However, recent research suggests BPS and other BPA analogs (bisphenol F, bisphenol AP, bisphenol AF, bisphenol Z, bisphenol B) have effects similar to, and are just as harmful as, BPA.
BPA induces breast cancer cell proliferation
BPA has been shown to increase proliferation of hormone receptor positive (ER+/PR+) breast cancer cells. BPA has also been shown to promote the migration and invasive properties of ER- breast cancer cells. Cell studies have also demonstrated that BPA could increase tumor size and grade in high-risk breast tissue in some circumstances.
Developmental exposure to BPA alters mammary glands
A variety of studies have used animal models to investigate the effects of exposure to BPA. One study that compared the effects of exposure to low doses of BPA or diethylstilbestrol (DES) during rat gestation and lactation found that both substances resulted in delayed mammary gland differentiation, altered milk yield and changes in milk composition. DES exposure has been linked to increased breast cancer risk.
Another study was designed to investigate the breast cancer-related developmental effects of low level prenatal exposure to BPA. The authors added bisphenol A to the drinking water of mouse breeding pairs. The mammary glands of the female offspring of these pairs were analyzed at puberty. The analysis demonstrated that estrogen-dependent events were modified and the number of terminal end buds (estrogen-induced proliferative structures which are considered to be targets of malignant transformation) was increased in a dose-dependent manner. In fact, adult female offspring had an increase in mammary epithelial cell numbers comparable to that seen in females exposed to DES. The authors concluded that perinatal exposure to environmentally relevant doses of bisphenol A alters long-term hormone response that may increase the propensity to develop breast cancer.
A 2012 study reported that BPA altered the fetal mammary gland development of rhesus monkeys. Pregnant rhesus monkeys were fed BPA daily from the 100th day of pregnancy onwards. The dosing resulted in circulating BPA levels comparable to that found in humans. A control group did not received BPA. The density of mammary buds was higher and the development of the mammary glands was accelerated in BPA-exposed daughter monkeys compared to unexposed monkeys.
Chronic low-level BPA exposure in adult mice increases tumor development
Another study examined the influence of chronic oral exposure to BPA during adulthood on mammary carcinogenesis. Mice that spontaneously develop HER2 overexpressing tumors were given drinking water with various levels of BPA. Only low doses of BPA were found to significantly accelerate mammary tumor development and metastasis.
BPA induces cell proliferation in BRCA1-deficient mice
The biological response to BPA appears to depend, in part, on an individual's genetic makeup. One study that was designed to investigate whether the loss of BRCA1 function could influence BPA-mediated cell proliferation reported that loss of BRCA1 enhanced BPA-induced cell proliferation (at BPA levels comparable to current human BPA exposure). BPA administration was found to stimulate mammary cell proliferation in BRCA1 mutant mice, leading to hyperplasia. The authors concluded that biological responses in BRCA1-deficient cells might depend on environmental exposures, such as exposure to BPA.
BPA can interfere with effectiveness of treatment
BPA at low concentrations has been shown to reduce the efficacy of the chemotherapy drugs Adriamycin (doxorubicin), cisplatin, and vinblastine in both estrogen receptor positive (ER+) and triple negative (ER-/PR-/HER2-) breast cancer cells. In addition, recent evidence indicates it could interfere with the effectiveness of tamoxifen treatment. Despite BPA's estrogenic properties, its effects are not necessarily mediated only through cancer cell estrogen receptors. BPA appears to induce chemoresistance by increasing expression of anti-apoptotic proteins (which prevent programmed cell death).
Taking steps to reduce exposure to bisphenol A makes sense
The role of BPA in human health is controversial. There are strong opinions on both sides; some observers believe that the health effects of typical exposure to BPA are likely trivial. The Food and Drug Administration (FDA) issued an update of its policy regarding BPA in March 2012, rejecting a ban on BPA in containers, finding BPA safe as currently used, but willing to consider new evidence as it becomes available. However, note that European regulations are stricter with regard to potential BPA exposure and consumers there appear to enjoy a higher level of protection.
Proponents of the view that typical BPA exposure does not present a health hazard point to the unrealistic aspects of some BPA experiments, including high doses and administration of BPA to rats by injection (whereas most human exposure is oral). BPA is quickly metabolized and detoxified when ingested by enzymes that convert it into BPA-glucuronide, a harmless water-soluble chemical that is easily excreted in urine, according to some research.
However, as the studies mentioned above show, cancer researchers have addressed methodological issues by testing low doses of BPA and administering it to animals orally. In both cases, BPA retains its cancer-promoting effects. Also, as the soup experiment described above demonstrates, it is possible to generate high urinary levels of BPA simply by eating canned soup every day. Therefore, we think it makes sense to take steps to reduce exposure to BPA, especially during chemotherapy. BPA exposure can be limited by avoiding canned foods, canned sodas, and polycarbonate plastic bottles and food containers. Some plastic containers are marked with a recycling number in a triangle-shaped icon (usually on the bottom). Plastics marked with the number 7 should be avoided since they incorporate polycarbonate, which contains BPA. Some plastics marked with the number 3 also contain BPA. There is also some evidence that consuming turmeric could mitigate the harmful effects of exposure to BPA.
Below are links to recent studies on this topic. For a more complete list of studies, please click on BPA.