Daughters of women who have been diagnosed with breast cancer or who have a BRCA1 or BRCA2 mutation are at higher risk for breast cancer than the general population. While there are some breast cancer risk factors such as height and age at first period over which parents have limited control, there are other sources of risk that they can influence. These generally fall under diet and lifestyle factors, although minimizing exposure to certain pollutants and ionizing radiation are also important. This topic has been divided into three time periods: prenatal period and infancy; childhood and puberty; and teenage years and young adulthood.
Avoiding early puberty
Established risk factors for breast cancer include early age at menarche (first period), which increases premenopausal cumulative estrogen exposure. A diet rich in fruits and vegetables with high vitamin A content has been found to delay sexual maturation and carcinogen-induced mammary tumors in rats. On the other hand, consumption of high-carbohydrate drinks (i.e., soft drinks or soda), processed meats, and shellfish during childhood each have been found to be associated with early puberty in girls.
Some personal care products have been found to cause signs of sexual maturation in girls (and feminization, including breasts, in boys). These include shampoo and other hair products, body creams, body oils, and other personal care products with labels indicating that they contain lavender or tea tree oil.
Personal products containing parabens are also suspected of contributing to breast cancer incidence. These products are intended for external use, but are absorbed through the skin or scalp. Sunscreens and other UVF-rated personal care products containing benzophenones, octylmethoxycinnamate, 4-methylbenzilidenecamphor or homosalate should be avoided. In addition, there are a number of hair care and other products marketed to African-American women that contain placenta or "hormone" that should be avoided.
Childhood milk consumption and breast cancer
Although milk consumption during adulthood has been found to be associated with higher risk of breast cancer, milk has previously been found to be somewhat protective against breast cancer when consumed in infancy and childhood. A partial explanation proposed for this finding is the fact that milk is a very good source of calcium and vitamin D, both of which are known to protect against breast cancer. Exposure to estrogen during childhood also appears to be protective against subsequent breast cancer, although the mechanism of action is not understood. Milk consumption is also associated with higher bone mineral density and other measures of bone health.
Based on the available evidence, the point in time during which milk becomes a risk factor in U.S. girls appears to be late adolescence. We would recommend organic milk (from grass-fed cows, if possible), but not raw milk, for consumption by our children. Non-organic milk contains additional recombinant bovine growth hormone, zeranol and other additives administered to cows and sheep. Raw milk could be a source of bovine leukemia virus (BLV), which has been reported to be associated with increased breast cancer risk.
Childhood exposure to oncogenic viruses
Certain viruses have been reported to be associated with breast cancer. These include mouse mammary tumor virus (MMTV), bovine leukemia virus (BLV), Epstein-Barr virus, human papilloma virus (HPV), human cytomegalovirus (Human Herpes virus 5), and measles virus. The topic is controversial, in part because of problems with methodology and inconsistent findings. In any case, it makes sense to reduce or avoid exposure to these viruses.
Steps should be taken to avoid transmitting herpes to children during pregnancy or childbirth. Children should be vaccinated against measles as young toddlers and HPV as older children. Children should not be served raw milk and uncooked beef, both of which are possible sources of BLV infection, as noted above. Although it is possible that MMTV is more often transmitted between humans rather than being passed directly from mice, it makes sense to avoid exposing children to mice, including pet mice.
Childhood soy consumption and breast cancer
Numerous studies have found that soybean consumption in childhood is associated with lower risk of breast cancer in adulthood. The soybean products that are protective are not the highly processed forms of soy most often consumed in the U.S., namely soy protein isolate and soybean oil. Nor are they highly salty soy products such as miso soup, soybean paste and soy sauce. Rather, they include less processed forms of soy, such as tofu and edamame, which are typically consumed as protein or vegetable components of meals.
Childhood weight and breast cancer
Established risk factors for breast cancer also include tall stature, which is associated with higher levels of various growth hormones. Weight should not be confused with height. While obesity is associated with increased risk of postmenopausal breast cancer in adult women, being somewhat overweight appears to be protective against breast cancer before menopause. This is true also of childhood. Girls should not be deprived of needed calories in an effort to delay puberty. It is the tall, thin girls who go on to have the highest rates of premenopausal breast cancer. However, one study found that the associations of childhood height and weight with risk of breast cancer held only for women without a family history of breast cancer.
Childhood exercise and breast cancer
There is some evidence that vigorous exercise during childhood reduces the subsequent risk of breast cancer. There is also evidence that adequate vitamin D prevents breast cancer. Exercise can also help prevent early puberty. Based on the available evidence, it makes sense for our high risk daughters to participate in outdoor sports and other regular physical activity during childhood. It is important to take steps to avoid sunburn, but girls should be allowed to regularly expose their skin to sunlight. This includes African Americans and other girls of color.
Omega-3 vs. omega-6 fatty acids and breast cancer
A diet with a relatively low omega-6 to omega-3 fatty acid ratio is protective against breast cancer in adults and appears to be so in children also. However, several studies have found that prepubertal rats fed diets very high in omega-3 fatty acids can have unwanted effects, including adverse effects on the prepubertal mammary gland and an increase in subsequent breast cancer risk. While it makes sense to introduce fatty fish in the diets of children, fish oil supplementation does not appear wise. Using olive oil and walnut oil in preparing meals instead of high omega-6 oils such as corn oil, sunflower oil and soybean oil also appears logical given evidence from available animal studies, but there are no population studies that the support the hypothesis that childhood consumption of these oils influences breast cancer risk in adulthood.
Environmental carcinogen exposure and breast cancer
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 (BPA), 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 soup and soda can linings, plastic baby bottles, water bottles, and clear plastic sippy cups. Children and adults alike should avoid all but temporary, low temperature uses of these products. 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.
Girls who are raised on or near farms, raised by farm workers, 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. Girls 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. Parents of girls raised on or near farms should educate themselves on the risks of the specific chemicals used there and take appropriate precautions.
Household insecticides containing lambda-cyhalothrin should also be avoided, since this chemical has been found to have estrogenic properties, including promoting the growth of hormone receptor positive breast cancer cells in the laboratory.
Exposure to second-hand cigarette smoke during childhood has been found to be associated with increased risk of breast cancer in adulthood.
Sleeping in the presence of light (including night lights, light entering through windows, and light from television screens), which reduces melatonin production, has been found to increase risk in adult women and might also increase risk during puberty.
Childhood radiation exposure and breast cancer
Whether used to treat or to diagnose illness, radiation to the chest or back (including x-rays, CT scans, and radiation treatment) during childhood can result in breast cancer in adulthood. While such radiation normally is administered for medically necessary reasons, parents of girls at high risk for later breast cancer should pay attention to the degree of exposure and try to limit it, where possible. Parents should also make sure that the chest is fully protected when radiation is administered to the head or neck or other areas close to the chest or back.
Foods and spices to include during childhood and puberty
The following foods and spices may reduce the subsequent risk of breast cancer in women when included in the diet during childhood and puberty:
Foods and products to limit or avoid during childhood and puberty
The following foods and products may increase the subsequent risk of breast cancer in women when consumed or used regularly during childhood and puberty:
- French fries
- Processed meats (e.g., bacon, hot dogs, bologna, sandwich meats, pepperoni)
- Red meat (beef, pork, lamb)
- Soda and other high-carbohydrate drinks
Mothers who themselves have an elevated risk of breast cancer should eat a wide variety of the foods on our recommended food list and limit or avoid those on our avoid list, in addition to paying particular attention to the foods and other products on the lists above when feeding their children.
Below are links to recent studies on this topic. For a more complete list of studies, please click on protecting our children.