A new study has reported that high levels of estrogens, androgens and insulin-related growth hormones contribute to risk of breast cancer in postmenopausal women. The higher the hormone levels and the greater the number of hormones with elevated levels, the greater the risk. Sex and growth hormones are known to be positively associated with postmenopausal breast cancer. However, few studies have examined the simultaneous influence of multiple hormones.

The study included 265 breast cancer cases and 541 matched cancer-free controls in the prospective Nurses' Health Study. Pre-diagnosis levels of estrogens (estradiol, estrone, estrone sulfate), androgens (testosterone, androstenedione, dehydroepiandrosterone (DHEA), DHEA sulfate), prolactin, insulin-like growth factor (IGF-1) and c-peptide were considered alone and in combination as breast cancer risk factors. The authors created hormone scores that (1) ranked the women by the number of hormones with above average levels; and (2) weighted the hormone values according to their individual associations with risk of breast cancer.

Women with the top fifth of individual estrogen or androgen levels were found to have approximately twice the risk of postmenopausal breast cancer as those in the lowest fifth. Seven or eight hormones above their geometric averages compared to no hormones at above average levels was associated with a 2.7-fold increase in overall breast cancer risk and 3.4-fold increase in risk of estrogen receptor positive (ER+) breast cancer. In other words, while the risk increased more for ER+ breast cancer, it was also significantly elevated for ER- breast cancer among women with high hormone levels. The number of different hormones with elevated levels influenced the degree of increased risk: women with one elevated hormone had a 10% increased risk (compared to normal levels); women with five or six elevated hormones had twice the risk; and women with seven or eight elevated hormones had triple the risk. The results held when adjusted for body mass index (i.e., being overweight was not an explanation for the associations). The authors conclude that having multiple hormones with high circulating levels substantially increases the risk of postmenopausal breast cancer, particularly for ER+ disease.

In a separate interview, study author Shelley Tworoger said, "Elevated estrogens had the biggest effecton risk, especially for ER positive cancer. However, androgens,and prolactin also contribute to increasing risk of breastcancer. These hormones are known to stimulate the growth of breast cancer cells in the lab and, while androgens can be converted to estrogens in the body, these hormones have also been found to stimulate cancer cell growth in the absence of ER. Our results suggest that models used to assess breast cancer risk could be improved by taking into account multiple sex hormone and growth hormone levels."

Comments regarding the study

The issue of levels of sex hormones in the blood and breast cancer risk and prognosis is complex and the solution is far from straightforward. Adjuvant anti-estrogen treatments such as tamoxifen and aromatase inhibitors are designed to reduce the level of estrogen available to promote hormone receptor positive breast cancer growth. However, breast cancer typically develops resistance to these treatments over time and metastases not infrequently have different receptor status from the original tumor. Having said this, it appears to be clear that women in the U.S. are exposed to multiple sources of estrogen and other hormones through food, personal products and environmental exposures and that reducing or mitigating these exposures would reduce the risk of breast cancer or breast cancer recurrence in some women.

Personal care products

Personal care products including shampoos and other hair care products, body creams, body oils, and other products for external use containing lavender, tea tree oil, placenta or placental extract, hormones or parabens should be avoided. These include products containing "natural" estrogens that are marketed to counteract "hormonal aging." These products are intended for external use, but are absorbed through the skin or scalp. A number of hair care and other products marketed to African-American women contain placenta or "hormone" and should be avoided.

Use of birth control pills at young age

While use of birth control pills during adulthood has not been connected to breast cancer risk, birth control pills and other forms of hormonal contraception started at a young age have been found to increase the subsequent risk of breast cancer. For example, one 2010 study found that oral contraceptive use was associated with an almost three-fold increase in the risk of triple negative (ER-/PR-/HER2-) breast cancer among women of 45 to 64 years of age who had begun to use oral contraceptives before age 18. While the use of contraceptive injections and implants have not been widely studied, implants appear to have the greatest potential to increase breast cancer risk, whereas injections appear comparable to birth control pills.

HRT and bioidentical hormones

Hormone replacement therapy (HRT) has been found to be associated with increased risk of breast cancer, especially estrogen receptor positive (ER+/PR+ or ER+/PR-) and lobular breast cancer. Strong evidence that HRT (conjugated equine estrogen combined with progestin) use could increase the risk of breast cancer was first published in 2002, when it was reported that participants in the Women’s Health Initiative (WHI) randomized trial who were taking HRT had higher rates of breast cancer than those who did not. Subsequent studies have confirmed the finding that HRT promotes breast cancer. While HRT is effective in reducing menopausal symptoms such as hot flashes, women are advised to use HRT for the shortest possible period for the relief of severe menopause-related symptoms.

Bioidentical hormone formulations, which have been described by some health practitioners as more natural and safer than conventional HRT, have been welcomed by many women who seek relief from menopause-related symptoms. Bioidentical hormones are plant-derived hormones that are biochemically identical or similar to those produced in the body, especially those produced by the ovaries. Some prescription products that contain bioidentical hormones are FDA approved. However, bioidentical hormones that are custom-compounded have not been tested for purity, potency, efficacy, and safety. Unfortunately, large-scale and carefully designed population studies comparing HRT with bioidentical hormone treatments are not available.

The main danger of unregulated bioidentical hormone treatments is that women may be exposed to high levels of estrogen (potentially higher than HRT) that could promote breast cancer. The sense of well being that some women report while using bioidentical hormones may in fact be the result of dangerous levels of estrogen and other hormones. The promises that were once made for HRT, including various aspects of youthfulness in addition to the relief of symptoms such as hot flashes and vaginal dryness, are now being made for compounded bioidentical hormone treatments. Neither are safe for women at high risk for breast cancer or its recurrence.

Estrogenic chemicals in plastics

Some plastics contain estrogenic and otherwise carcinogenic chemicals that can leach into food when the plastics are heated, microwaved, put under pressure or simply scuffed and worn. These chemicals include bisphenol A, styrene, and phthalates. Plastics that may leach these substances include (1) polyvinyl chloride (PVC), which may be found in cling wrap, some plastic squeeze bottles, and cooking oil bottles; (2) polystyrene, which may be found in styrofoam food containers and disposable cups and bowls; and (3) polycarbonates, which may be found in plastic baby bottles, water bottles, and clear plastic sippy cups. All but temporary, low temperature uses of these products should be avoided. Plastic containers may be marked with a number in a triangle-like icon. Plastics marked 1, 2, 4 or 5 use less toxic additives in their manufacture. Products that use polyvinyl chloride should be marked with 3, polystyrene with a 6, and polycarbonate with a 7 - these are the ones to avoid.

Contaminants in drinking water

The EPA has not been properly enforcing U.S. standards for clean drinking water in recent years. Contaminated drinking water has been linked to cancer in numerous studies. The most important potential water contaminant contributing to increased breast cancer risk appears to be cadmium, which has also been shown to have estrogenic effects. Certain industrial chemicals, including alkylphenolic compounds such as 4-octylphenol, and persistent organochlorine compounds such as perchloroethylene (tetrachloroethylene), can also increase risk, however such contamination is not widespread.

The risk of contamination appears to be concentrated in smaller water systems which have fewer resources to improve water quality and whose populations may not be as vigilant in monitoring it. However, parts of some major population centers are served by wells or source their water from areas that may be polluted. We would suggest doing some research on local water quality. Possible sources of information are local newspapers, websites of environmental advocacy groups, and the EPA itself. If you are not satisfied with the level of detail available for your area, it might be worthwhile to order a kit to have the water in your house tested.

Agricultural, manufacturing and workplace exposures

Women living on or near farms or who are themselves farm workers are especially vulnerable to the breast cancer-promoting effects of certain pesticides, hormones and other chemicals used in the production of food and other products. Ideally, women should be kept out of harm's way when such chemicals are applied and should not be required to pick or process crops to which pesticides have been applied. This includes greenhouse crops. Although not all crops are grown with the assistance of carcinogens, some crops are associated with particularly high rates of breast cancer among workers. For example, one study found that California mushroom workers had approximately six times the expected incidence of breast cancer. Women living on or near farms should educate themselves on the risks of the specific chemicals used there and take appropriate precautions. High risk women would also be better off not working in or near auto repair shops, gas stations, chemical plants, certain military bases, and recycling or waste disposal facilities.

Foods that can mitigate estrogen exposure

The following foods have been found to counteract estrogenic substances in the diet directly or by inhibiting aromatase (the synthesis of estrogen from androgens within the body), and have also been associated with reduced risk of breast cancer:

Dietary, fiber
Grapes, red
Green tea
Honey, minimally processed
Lake trout

Mushrooms, white button
Pomegranates & pomegranate juice
Salmon, wild

Studies have produced conflicting results concerning the impact of the soy phytoestrogens genistein and daidzein on breast cancer risk, however, we recommend against supplementation with any phytoestrogens.

Regular exercise has been shown to reduce circulating hormone levels even in the absence of weight loss.