Apples (Malus domestica or Malus pumila) belong to the Rosaceae family. Apples are a very good source of phloretin, fisetin, ursolic acid and fiber, as well as anthocyanins (red peeled varieties), all of which have anti-cancer properties. Apples also incorporate betulinic acid, chlorogenic acid, catechin, epicatechin, oleanolic acid and ferulic acid.
The peel has the most micronutrients, however, nonorganic apple peels are likely to be contaminated with pesticides. Red, red-streaked or rosy apples have more antioxidant and antiproliferative phytochemicals than green or yellow apples.

Breast cancer-related effects of eating apples

Apples and apple compounds have been shown to prevent or inhibit breast cancer or its progression in human, animal and cell studies.

Epidemiological studies

Several studies have reported that the consumption of apples is associated with reduced risk of breast cancer, including when the results were adjusted for factors such as age, education, body mass index (BMI), and physical activity. One study reported that adolescents with high apple intake had reduced risk of breast cancer in adulthood.

Animal studies

An apple peel diet significantly inhibited the growth of mammary tumors in a mouse model of breast cancer in one study. The same study reported that a triterpenoid found in apple peel induced apoptosis (programmed cell death) in triple negative (ER-/PR-/HER2-) breast cancer cells.
Apples have been shown to shrink the size of mammary tumors in rats and to induce apoptosis (programmed cell death) in both hormone receptor positive (ER+/PR+) and triple negative breast cancer cells. Apple peel contains chemicals that appear to be important for this effect.

Phloretin

The apple flavonoid phloretin has been shown to reduce the growth and migration of both ER+/PR+ and triple negative breast cancer cells. Phloretin has also been reported to increase the anti-cancer effects of the chemotherapy drugs Adriamycin (doxorubicin), Taxol (paclitaxel) and cisplatin, as well as potentiating the treatment effects of tamoxifen and Herceptin. In fact, phloretin has been shown to reverse multidrug resistance in cancer cells. Phloretin has also been demonstrated to have anti-tumorigenic effects in mouse models of breast cancer and to reduce Adriamycin-induced heart damage (cardiomyopathy).

Fisetin

The apple favonol fisetin has been demonstrated to inhibit the growth and migration of triple negative breast cancer cells, thus helping prevent metastasis. Fisetin has also been reported to induce programmed cell death in ER+/PR+ breast cancer cells while not harming normal breast cells. In addition, fisetin has been shown to inhibit the formation of a carcinogenic compound, 4-hydroxy-E2 (4-OHE2), from estradiol (E2), the most important estrogen.

Ursolic acid

Ursolic acid, which is found in apple peels, has been shown to reverse multidrug resistance in breast cancer cells. One study found that ursolic acid reversed resistance to Taxol in Taxol-resistant triple negative breast cancer. Another study reported that ursolic acid resensitized multidrug resistant ER+/PR+ breast cancer cells to Adriamycin chemotherapy. Still another study reported that ursolic acid increased the sensitivity of triple negative breast cancer cells to Adriamycin.

Apple cider and apple cider vinegar

Apple cider is produced by fermenting apple juice, resulting in alcohol content of 1% to 9%. The polyphenols in cider depend on a number of factors, however, the apple variety is most important. Hence apple cider made from pink- or red-skinned apples with high flavonol content has a more beneficial profile than cider made from yellow or green apples. The most abundant chemopreventive polyphenols in apple cider include the hydroxycinnamic acids chlorogenic acid, caffeic acid, ferulic acid, and p-coumaric acid. Apple cider produced by fermenting apple juice with probiotics contains a similar mix of hydroxycinnamic acids. Like cloudy (i.e., not highly filtered) apple juice, apple cider is also a source of quercetin and phloretin.
Apple cider vinegar is produced by adding bacteria to apple cider, which eliminates the alcohol by turning it into acetic acid. Chlorogenic acid is the major phenolic acid in apple cider vinegar. It has strong antioxidant properties and has been reported to reduce tamoxifen-associated liver and kidney damage in rats. However, chlorogenic acid does not appear to have significant chemopreventive properties with respect to breast cancer. Apple cider vinegar also contains a small fraction of caffeic acid and little ferulic acid and p-coumaric acid. Apple cider vinegar is sometimes used as an alternative medication to treat type 2 diabetes, high cholesterol, cancer and other conditions, as well as to encourage weight loss.
Apple cider vinegar is sometimes proposed as having more health benefits than apples or apple juice because the fermentation process converts polyphenols into small phenolic molecules with higher biologically availability and activity that those in apples or apple juice. However, the animal experiments that have been performed to test this theory have focused on type 2 diabetes and aspects of cardiovascular disease such as hypertension, not cancer. The one breast cancer-related animal study of which we are aware reported that apple cider vinegar reduced the levels of estrogen and testosterone but increased the levels of progesterone in experimental rats, a finding that does not lead to any dependable conclusions with respect to breast cancer.
In fact, using apple cider vinegar as a treatment has its own risks. For example, it can contribute to low potassium levels and osteoporosis, which means that it should not be used by those taking an aromatase inhibitor (who are therefore already at risk for poor bone health). Eating apples and drinking cloudy apple juice provides multiple beneficial micronutrients with respect to breast cancer without the potential for any harmful side effects. We do not recommend using apple cider vinegar as a supplement.

Additional comments

It is worthwhile to buy organic apples

Organic U.S. apples are the best choice. Conventionally grown apples typically are produced using relatively high levels of pesticides. Such apples are normally washed after picking, which removes some of the pesticide residue, but also strips off some of the natural apple wax (the waxy cuticle, which contains ursolic acid and other compounds) that is part of the peel. Food grade wax is then applied to the apples, which can seal in some of the remaining pesticide residue. Non-organic apples must be washed very thoroughly to remove pesticide residue as much as possible.

Most apple juice is undesirable

Apple juice is not particularly beneficial compared to raw apples, however cloudy apple juice has more antioxidants than clear apple juice. Apple juice processing and filtering removes some of the nutrients and fiber found in apple pulp.
Apple seeds contain amygdalin, a compound which incorporates cyanide that can be released if the seeds are chewed, crushed or ground. It would take hundreds of crushed seeds to cause cyanide poisoning. Still, removing the seeds before preparing your own apple juice makes sense.
There have also been reports of meaningful levels of arsenic in apple juice produced from apples grown in countries that use certain pesticides no longer approved for use in the U.S. According to the FDA, even U.S. organic apples can come from trees grown in soil that may contain arsenic. This is because arsenic-based pesticides were commonly used in the U.S. until 1970, leaving traces that persist in some soils. However, the situation in other countries can be far worse. Unfortunately, it can be difficult to determine where the apple juice concentrate used to make juice is sourced. Asia and South America are major suppliers of apple juice concentrate used in the U.S.

Sources of information provided in this webpage

The information above, which is updated continually as new research becomes available, has been developed based solely on the results of academic studies. Clicking on any of the underlined terms will take you to its tag or webpage, which contain more extensive information.
Below are links to 20 recent studies concerning this food and its components. For a more complete list of studies, please click on apples.