Brussels sprouts (Brassica oleracea var. gemmifera), like broccoli and cabbage, are cruciferous vegetables. Brussels sprouts are the source of a variety of compounds with suspected or demonstrated breast cancer fighting properties. Brussels sprouts have been shown to suppress inflammation and to reduce the risk of prostate, ovarian, cervical and colorectal cancer, among others.
Brussels sprouts are a good source of chemopreventive isothiocyanates, including allyl isothiocyanate (AITC), indole-3-carbinol (I3C) and its metabolic product 3,3'-diindolylmethane (DIM), and sulforaphane. In addition, brussels sprouts are a good source of beta-carotene, vitamin C and vitamin K.

Breast cancer-related effects of eating brussels sprouts

Brussels sprouts consumption is associated with reduced breast cancer risk. Brussels sprouts compounds have been found to be promote apoptosis, suppress cell cycle progression and inhibit angiogenesis of human breast cancer cells. Futhermore, Brussels sprouts can protect against cell DNA damage. Brussels sprouts can increase the beneficial effects of some breast cancer treatments. Heavily cooking Brussels sprouts greatly reduces their potential effectiveness in preventing breast cancer or its relapse.

Epidemiological studies

A number of population studies have found a lower risk of breast cancer associated with consumption of one or more cruciferous vegetables. For example, one study based on Italian and Swiss populations reported that consuming cruciferous vegetables at least once per week was associated with a 17% lower risk of breast cancer compared with never or only occasionally consuming cruciferous vegetables.

Brussels sprouts can increase treatment effectiveness

DIM and I3C have been shown to enhance the therapeutic efficacy of the chemotherapy drugs Adriamycin (doxorubicin), Taxol (paclitaxel) and Taxotere (docetaxel) in breast cancer cells. For example, the combination of DIM plus Taxol has been reported to increase the death of HER2 overexpressing (HER2+) breast cancer cells more than Taxol alone in one study.
Brussels sprouts component sulforaphane has been shown increase the anti-cancer effects of Adriamycin, cisplatin, 5-Fluorouracil (5-FU), Taxol and Taxotere. For example, the combination of sulforaphane plus cisplatin has been shown to synergistically inhibit key steps of metastatic cellular growth in triple negative (ER-/PR-/HER2-) breast cancer cells.
Cruciferous vegetables are recommended during aromatase inhibitor treatment in part because several isothiocyanates have been shown to reduce aromatase expression, thereby helping to block the production of estrogens from androgens within the body. Breast cancer patients taking tamoxifen who also had relatively high cruciferous vegetable intake were less likely to experience a recurrence than tamoxifen users with low consumption in one study.

Important micronutrients in Brussels sprouts

Brussels sprouts isothiocyanates

Urinary isothiocyanate levels have been found to be related to lower breast cancer risk among both premenopausal and postmenopausal women.
AITC
Oral administration of AITC has been demonstrated to restore levels of proliferation and aromatase activity to near normal levels in a rat model of breast cancer. Another rat study found that AITC prevented mammary tumor angiogenesis and invasion. A 2021 study reported that AITC induced ER+/PR+ breast cancer cell death in a dose-dependent manner by causing DNA damage and altering DNA damage repair proteins.
I3C and its metabolic product DIM
Brussels sprouts are a particularly good source of I3C/DIM. Numerous studies have reported that I3C and DIM reduce the growth, proliferation and migration of various types of breast cancer cells. For example, I3C has been shown to inhibit proliferation of estrogen receptor positive (ER+) breast cancer cells. I3C/DIM has also been shown to inhibit aromatase (the conversion of androgens to estrogens) in both normal and ER+/PR+ breast cancer cells at concentrations in the range of that observed in human plasma.
DIM has been shown to inhibit the growth of transplanted human breast cancer cells in mice. In a separate study, DIM administered to mice injected with cancer cells caused a marked reduction in the number of lung metastases.
Sulforaphane
Sulforaphane has been shown to reduce triple negative breast cancer growth. A relatively low concentration of sulforaphane has been demonstrated to preferentially eliminate breast cancer stem cells from triple negative cells.
Mice were implanted with breast cancer tumors and the tumors were treated directly with sulforaphane in one experiment. Daily injection with sulforaphane for two weeks was found to reduce the number of stem cells by more than 50% in the xenograft tumors.
Sulforaphane has also been shown to inhibit aromatase in both normal and ER+/PR+ breast cancer cells at concentrations in the range of that observed in human plasma.
Sulforaphane has also been demonstrated to inhibit Herceptin-resistant HER2+ breast cancer.

Beta-carotene

Women with substantial intake of carotenoids appear to have lower risks of breast cancer and its recurrence than those with low intake, although not all studies have found such links. A Scandinavian study found that dietary (but not supplemental) beta-carotene had a protective effect against lobular breast cancer in postmenopausal women. Another European study reported that high intake of beta-carotene was protective against breast cancer in postmenopausal women using hormone replacement therapy (HRT). The same study also found that dietary beta-carotene was associated with lowered risk of breast cancer in postmenopausal women with relatively high alcohol consumption.
Beta-carotene enhanced the cytotoxicity of Adriamycin in both hormone receptor positive (ER+/PR+) and triple negative (ER-/PR-/HER2-) breast cancer cells in one study. Beta-carotene has also been demonstrated to reduce multidrug resistance in cancer cells.

Additional comments

Brussels sprouts are most chemopreventive when prepared first by chopping and then lightly cooking (steaming, stir‐frying, blanching or microwaving), not by heavily cooking (boiling, stewing, or deep frying).
We recommend consuming Brussels sprouts and other cruciferous vegetables as food and against consuming broccoli pills and other supplements that have been enhanced to boost the proportion of isothiocyanates in these vegetables. There is some evidence that concentrated cruciferous vegetable extracts can act as estrogen agonists and promote breast cancer cell proliferation. For example, one study reported that while physiologically achievable doses of I3C reduced aromatase expression of ER+/PR+ breast cancer cells, higher doses induced its expression.
Also, the anticancer properties of Brussels sprouts are likely to be the result of synergistic interaction of its various chemical components - isolated components have successfully inhibited proliferation in the laboratory, but their efficacy and safety in humans needs to be evaluated in large scale clinical trials.
Some cruciferous vegetables such as Brussels sprouts contain thioglucoside compounds in sufficient amounts to potentially interfere with the formation of thyroid hormone in women with iodine deficiency.

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 list of studies that includes older research, please click on Brussels sprouts.