Blueberries (Vaccinium corymbosum) rank among the highest of all fruits in their capacity to destroy free radicals and have significant neuroprotective, cardioprotective and cholesterol-lowering properties. Blueberries are a very rich source of the anthocyanins delphinidin, malvidin, and petunidin and also contains some cyanidin and peonidin.
Blueberries are also a very good source of piceatannol and pterostilbene, a good source of catechins, chlorogenic acid, gallic acid, resveratrol, and ursolic acid, and contain some kaempferol, myricetin, quercetin, and vitamin C, all of which have been reported to have anti-cancer properties.

Breast cancer-related effects of eating blueberries

Blueberry consumption is associated with reduced breast cancer risk. Blueberries are a source of a great variety of compounds with anti-cancer activities, including micronutrients that have been shown to increase the beneficial effects of breast cancer treatment.

Epidemiological studies

Blueberry and berry intake have been reported to be associated with reduced breast cancer risk and recurrence in a variety of studies. For example, a large 2020 prospective study reported that each two servings of blueberries per week after diagnosis was associated with measurably lower breast cancer–specific mortality.

Animal studies

Dietary blueberry has been shown to reduce mammary tumor volume in animal models of breast cancer. For example, blueberry reduced triple negative (ER-/PR-/HER2-) proliferation (as measured by Ki-67) and increased cell death in mammary tumors in one mouse study. Another mouse study reported that a blueberry diet inhibited triple negative tumor metastasis.
Tissue analysis has demonstrated that blueberry-fed mice tumors have significantly, favorably altered expression of genes important to inflammation, cancer, and metastasis.

Cell studies using blueberry extract

Blueberry extract has been shown to exhibit antitumor activity against triple negative breast cancer cells and reduce their metastatic potential. For example, blueberry was shown to inhibit cell proliferation in triple negative cells with no effect on normal breast cells in one study. Blueberry also reduced the metastatic potential of triple negative cells through inhibition of cell motility in another study.

Blueberry micronutrients

Anthocyanins
Blueberries are a rich source of a variety of anthocyanins — closely-related plant pigments with chemopreventive properties that give the berries their rich color. Women in the highest quartile (fourth) of anthocyanin intake had significantly lower risk of breast cancer than those in the lowest quartile in one study.
Delphinidin has been demonstrated to inhibit carcinogen-induced transformation of normal cells into breast cancer cells. Delphinidin has also been reported to suppress the growth of hormone receptor positive (ER+/PR+), HER2+, and triple negative breast cancer cells. In addition, delphinidin has been found to inhibit angiogenesis and migration of triple negative breast cancer cells and to reduce tumor growth in a mouse model of triple negative breast cancer.
High dietary intake of malvidin and peonidin have both been reported to be associated with reduced levels of systemic inflammation (as measured by CRP). Malvidin has also been shown to reduce the growth and proliferation of ER+/PR+ breast cancer cells. Peonidin and cyanidin have both been reported to suppress angiogenesis by inhibiting proliferation and migration.
Peonidin and cyanidin have also been found to induce programmed cell death (apoptosis) in HER2+ breast cancer cells and to reduce tumor size and volume in an animal model of HER2+ breast cancer. In addition, peonidin and cyanidin have been shown to increase the treatment effects of Herceptin (trastuzumab) in HER2+ cells.
Petunidin has been demonstrated to reduce growth and proliferation of ER+/PR+ breast cancer cells.
Anthocyanins have also been demonstrated to reduce Adriamycin (doxorubicin) chemotherapy-induced heart damage.
Gallic acid
Gallic acid has been shown to increase the effectiveness of Taxol (paclitaxel) chemotherapy in ER+/PR+ breast cancer cells.
Piceatannol
Piceatannol has been shown to inhibit the migration and growth of normal breast cancer cells treated with a tumor promoter, in effect blocking the transformation of the cells into cancer cells. Piceatannol has also been demonstrated to reduce the invasion and migration of triple negative breast cancer cells without affecting the viability of normal cells. In addition, piceatannol has been reported to induce programmed cell death of ER+/PR+ breast cancer cells.
Pterostilbene
Pterostilbene has been shown to inhibit obesity-related breast cancer growth and proliferation in the laboratory and to have additive treatment effects when combined with tamoxifen in estrogen receptor positive (ER+) breast cancer cells. Pterostilbene has also been shown to significantly increase the cytotoxic effects of Taxol.
Pterostilbene has also been demonstrated to reduce the formation of breast cancer stem cells and inhibit their metastatic activities. In addition, pterostilbene has been found to reduce expression of mutant p53 in triple negative and ER+/PR+ cells, thereby inhibiting the development and progression of breast cancer.
Resveratrol
Blueberries are also a source of resveratrol, which has been shown to increase the cytotoxic effects of radiation treatment and the chemotherapy drugs Adriamycin and Taxol against breast cancer. Resveratrol has also been reported to potentiate tamoxifen treatment and to inhibit aromatase (the synthesis of estrogen from androgens within the body), thereby strengthening the treatment effects of aromatase inhibitors.
Resveratrol has also been found to inhibit lung metastasis in a mouse model of triple negative breast cancer. Resveratrol has also been demonstrated to help protect against cisplatin-induced ovarian and uterine damage.
Ursolic acid
Ursolic acid forms the waxy coating of fruits such as cranberries and blueberries. Ursolic acid 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. Still another study demonstrated that ursolic acid increased the sensitivity of triple negative breast cancer cells to Adriamycin.

Additional comments

While frozen blueberries have lower vitamin C content than fresh berries, freezing does not appear to significantly lower blueberry anthocyanin levels. However, microwaving and cooking blueberries does significantly reduce their anthocyanin content.
The antioxidant properties of blueberries have been shown to be reduced when eaten with milk.
Non-organic blueberries must be washed very thoroughly to remove pesticide residue as much as possible.
Bilberries (Vaccinium myrtillus), which grow wild in much of northern Europe, are closely related to blueberries. They are also valued for their high flavonoid content, which is greater than that of blueberries in some respects. Bilberry extract has been shown to induce programmed cell death in ER+/PR+ breast cancer cells.

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 blueberries.