Daughters of those 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.

Exercise

Vigorous exercise during the teenage and young adult years has been found to reduce the risks of both premenopausal and postmenopausal breast cancer, although not all studies are in agreement. Since adequate vitamin D early in life also reduces the risk of breast cancer, it makes sense for teenagers and young women to participate in regular physical activity outdoors. While it is important to take steps to avoid sunburn and protect the face, exposing the arms and legs to the sun would enable the body to produce vitamin D. This is especially important for girls of color.

Diet

There is ample evidence that diet can influence risk of breast cancer in women. The following foods have been identified specifically as reducing subsequent risk of breast cancer when consumed during the teenage years:

Calcium-rich foods
High carotenoid foods
Fatty fish & other high omega-3 fatty acid foods
Fruit, especially apples, bananas, grapes & oranges, but not fruit juice
High fiber foods
Milk
Poultry
Soybeans
Tofu
Vegetables, especially carrots, kale, pumpkins & butternut squash
Yogurt
Vitamin D-rich foods
Although milk consumption during adulthood has been found to be associated with higher risk of breast cancer, milk has been found to be somewhat protective against breast cancer when consumed during the teenage years. A partial explanation that has been 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. Milk consumption during adolescence is also associated with higher bone mineral density and other measures of bone health. Organic milk (from grass-fed cows, if possible) is best since the cows are not given growth promoters. Raw milk should be avoided since it could be a source of bovine leukemia virus (BLV), which has been reported to be associated with increased breast cancer risk.

The following foods have been identified specifically as increasing subsequent risk of breast cancer when consumed during the teenage years:

Alcohol
Butter
Red meat
One 2016 study reported that relatively high consumption of saturated fat and low consumption of monounsaturated and polyunsaturated fats during the teenage years was associated with higher breast density (a breast cancer risk factor) in adulthood.

The foods listed above are just a few of the foods that have been found to be associated with risk of breast cancer when consumed by adults. We recommend that teenagers and young women 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 above.

Weight

While obesity is associated with increased risk of postmenopausal breast cancer in adult women, being overweight appears to be protective against breast cancer before menopause. This is true also of the teenage years. 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.

Anorexia nervosa

A study of Dutch World War II famine survivors found that they had higher subsequent risk of breast cancer. While starvation reduced growth, and resulted in later first period and earlier menopause (all of which would be expected to reduce the risk of breast cancer), levels of various estrogens and growth factors appeared to rebound after the famine ended, overshooting normal levels and resulting in a net increase in the risk of breast cancer. Exposure to famine between the ages of two and 10 was found to be an especially vulnerable period for the breast cancer promoting effects of calorie deprivation.

On the other hand, studies of the relationship between anorexia and/or bulimia nervosa and breast cancer risk have reported that anorexia or bulimia that occurs during the years up to age 25 actually is associated with reduced risk of breast cancer. The various findings on weight suggest that different weights are optimal during different periods of breast development. We suggest attempting to keeping girls and teenagers at normal weight, if possible. Most breast cancer occurs after menopause, when being overweight increases risk and when it becomes increasingly difficult to lose weight.

Breast self-exams

Teenagers should be taught how to perform breast self-exams and encouraged to perform them on a monthly basis. While rare, some aggressive breast cancers can occur during the teenage years and 20s.

Personal care products

Some personal care products contain estrogenic products that should be avoided. These include shampoo and other hair care products, body creams, body oils, and other products for external use containing lavender, tea tree oil, or parabens. These products are intended for external use, but are absorbed through the skin or scalp. Using vaginal douches can increase the level of phthalates that have been linked to increased breast cancer risk. Long-term use of antiperspirants or deodorants containing aluminum salts such as aluminum chlorohydrate could also increase the risk of breast cancer, especially if applied after shaving or when the armpits are irritated.

In addition, there are a number of hair care and other products marketed to African Americans that contain placenta or "hormone" that should be avoided. Teenage girls and young women should be discouraged from working in beauty salons where such products are used. There is also evidence that using hair dye can increase breast cancer risk.

Exposure to radiation

Whether used to treat or to diagnose illness, radiation to the chest or back (including x-rays, CT scans, and radiation treatment) during the teenage years can result in breast cancer in adulthood. While such radiation normally is administered for medically necessary reasons, parents of teenagers 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.

High risk women might also considering avoiding career choices such as airline pilot or cabin attendant that involve significant long-term exposure to radiation.

Harmful 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. Teenagers 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.

Exposure to agricultural and industrial carcinogens

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.

Occupational exposure to organic solvents prior to first birth has been linked to increased risk of breast cancer.

High risk teenage girls and young women would be better off not taking summer jobs or otherwise working in or near auto repair shops, gas stations, chemical plants, automotive plastics manufacturing plants, textile manufacturing plants, electrical manufacturing plants, food canning operations, dry cleaners, printers, recycling or waste disposal facilities, and military bases.

Exposure to light at night

Night shift work has been associated with increased risk of breast cancer in adult women, as has sleeping in the presence of light (including night lights, light entering through windows, and light from television screens). Exposure to light during normal sleeping hours interferes with melatonin production. Melatonin protects against breast cancer in several ways, including by reducing aromatase activity within the breast, thereby reducing estrogen production. Blue light wavelengths appear to have a far greater suppressive effect on melatonin production than red wavelengths, suggesting that girls should use red light when light is necessary (e.g., for alarm clock displays).

Acne treatments

Topical treatments containing tea tree oil have been shown to stimulate breast growth in children and should be avoided. Long-term use of antibiotics for treatment of acne or other conditions is suspected to increase the risk of breast cancer, although there is no consensus on this point. On the other hand, the use of Accutane (isotretinoin) for treatment of acne does not appear to increase the risk of breast cancer.

Herbal supplements designed to regulate menstruation

Some herbal supplements designed to regulate menstruation may promote breast cancer development. For example, one report described a 16 year old girl with large fibroadenomas (a type of benign breast tumor) who had been using Si-Wu-Tang, a traditional Chinese herbal preparation designed to treat irregular menstruation and abdomen pain, among other conditions. In a related study, discontinuing Si-Wu-Tang was found to reduce the size of fibroadenomas in a group of women with fibroadenomas. This is an alarming finding, given the association between benign breast disease and breast cancer. Use of birth control pills (which are also used to regulate menstrual cycles) by teenagers also has been found to increase risk of breast cancer (see below). It is important for teenagers to limit the period of time during which any hormonal preparations are used to regulate menstruation.

Birth control

Birth control pills and other forms of hormonal contraception started at a young age increase the subsequent risk of breast cancer. For example, one 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 45 to 64 years of age who had begun to use oral contraceptives before age 18. Use of levonorgestrel intrauterine system (LNG-IUS), an IUD-type device, has also been found to be associated with increased risk of breast cancer. 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.

HPV

The tumors of three of five women who developed breast cancer before age 25 contained a marker of HPV (human papilloma virus)-associated cancer in one 2009 study. While this finding is suggestive since breast cancer at such a young age is extremely rare, a link between HPV and breast cancer has not been firmly established.

Weight loss and fitness products

Care should be taken in selecting weight loss and fitness products. Soy-based protein powders and protein bars normally contain soy protein isolate. This is a highly processed estrogenic substance that does not have the health benefits of less altered forms of soy such as edamame or tofu and is not recommended for those at high risk for breast cancer. Supplemental human growth hormone might also contribute to breast cancer risk.

Breast implants and breast enlargement products

Cosmetic breast implants do not appear to increase the risk of breast cancer. However, breast cancer patients with breast implants tend to be diagnosed at a later stage and have poorer survival than those without implants. Preliminary evidence suggests that silicone breast implants may occasionally cause anaplastic large cell lymphoma, a rare type of non-Hodgkin lymphoma. On the other hand, breast reduction surgery has been shown to reduce the risk of breast cancer by reducing the volume of breast tissue that could develop cancer.

Pills and creams designed to increase breast size should be avoided. These products typically contain a variety of ingredients, for example wild yam, hops, saw palmetto, dong quai, chaste-tree berry, fennel, kava, black cohosh, and fenugreek. To the extent that some breast enlargement products work temporarily, it is because some of the component herbs are estrogenic.

Smoking

While smoking is not a major risk factor for breast cancer when begun in adulthood, both smoking before age 15 and smoking before giving birth for the first time have been found to increase the risk of breast cancer in later years.

Alcohol consumption

Adolescent alcohol consumption has been shown to increase the risks of subsequent proliferative benign breast disease and breast cancer, especially among those with a family history (mother, aunt, or grandmother) of breast cancer. This sets the stage for subsequent breast cancer.

Childbearing and nursing

Leaving aside personal preferences, career goals, and many other important factors, women at high risk for breast cancer are better off having children while young and nursing them. Some studies have reported that fertility treatments (assisted reproductive technology) could increase the risk of breast cancer. However, one 2015 study reported that while in vitro fertilization (IVF) was associated with substantially increased risks of ovarian and endometrial cancers, it did not appear to increase breast cancer risk.

Long duration of breastfeeding reduces the risk of breast cancer, especially the risk of triple negative disease in African-American women, although the impact on risk is not strong. However, one 2015 study reported that women who developed breast cancer who had not breastfed had a three-fold increased risk of breast cancer recurrence compared to those who breastfed at least three children. There is some evidence that short duration of breastfeeding (less than six months) might actually increase the risk of breast cancer as a result of the abrupt way in which the breast reverts to a non-lactating state (a process known as involution). Adequate (but not excessive) levels of zinc may also be important for maximizing the protective effects of breastfeeding.

While pregnancy itself temporarily elevates risk of breast cancer, this risk subsides after giving birth and the eventual result is a permanent reduction in risk (after approximately three years). However, this pregnancy-associated risk reduction may never take place for women who are obese at the time of pregnancy.

Several studies have reported that close spacing of births (under three years) and failures in breastfeeding (presumably because of defective breast maturation) heighten the temporary increase in breast cancer risk associated with being pregnant and having children. However, a Finnish study found that, for women who first gave birth under age 30, having another baby within 18 months reduced the eventual risk of breast cancer after age 50 (but increased this risk in women who first gave birth after age 30).

One meta-analysis of previous studies reported that ever breastfeeding preferentially reduces the risk of triple negative breast cancer among women who have given birth, but does not appear to affect the risk of other types of breast cancer.

Greater number of pregnancies and younger age at first live birth have been found to be associated with lower risk of breast cancer in young women with benign breast disease. Benign breast disease is significantly less likely to progress to breast cancer in women who have children before age 25 and who have several children.

Young women should limit or avoid consuming fish, shellfish and caviar and other sources of polychlorinated biphenyls (PCBs) during pregnancy and nursing. High PCB levels have been associated with low birth weight. In addition, elevated levels of PCBs when the breast undergoes changes associated with lactation are associated with increased risk of premenopausal breast cancer in the mother.

Women with BRCA1 mutations might find that their fertility may be impaired, especially as they age. Having children while young could enable some women to become mothers who might otherwise never have them because of premenopausal breast cancer. Also, the children are likely to be older if cancer does occur, leaving such women in a better position to focus on their cancer care. One possible strategy for extremely high risk women would be to have children and then undertake prophylactic surgery on the breasts and ovaries to reduce risks of breast and ovarian cancer.

Below are links to recent studies on this topic. For a more complete list of studies, please click on protecting our children.