Broccoli (Brassica oleracea var. italica) contains numerous compounds with cancer fighting properties, which have been linked to reduced risks of breast, ovarian, prostate, and colorectal cancers, among others. Broccoli is a good source of alpha-lipoic acid, beta-carotene, choline, folate, kaempferol, soluble fiber, vitamin C and vitamin K.
Broccoli, broccolini and broccoli sprouts also are good sources of chemopreventive isothiocyanates, including benzyl isothiocyanate (BITC), indole-3-carbinol (I3C) and its metabolic product 3,3'-diindolylmethane (DIM), and sulforaphane. Note that while rapini (Brassica rapa ruvo), or broccoli rabe, is a cruciferous vegetable that resembles broccoli, it is more closely related to turnip than broccoli.

Breast cancer-related effects of eating broccoli

Summary

Broccoli consumption is associated with reduced breast cancer risk. High urinary isothiocyanate levels have been reported to be linked to lower breast cancer risk among both premenopausal and postmenopausal women. Broccoli consumption has been shown to reduce the estrogen metabolite 16alpha-hydroxyestrone, which is a breast cancer promoter. Broccoli has been found to promote apoptosis, suppress cell cycle progression and inhibit angiogenesis of human breast cancer cells. Broccoli can increase the beneficial effects of some breast cancer treatments. Broccoli sprouts are particularly rich in anticancer nutrients. Boiling broccoli can significantly reduce its 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.

Broccoli 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 was reported to increase the death of HER2 overexpressing (HER2+) breast cancer cells more than Taxol alone in one study.
Broccoli 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.
Beta-carotene was demonstrated to enhance the cytotoxicity of Adriamycin in both hormone receptor positive (ER+/PR+) and triple negative breast cancer cells in one study. Beta-carotene has also been demonstrated to reduce multidrug resistance in cancer cells.
Broccoli compound kaempferol has been shown to reduce the degree of heart and kidney damage caused by Adriamycin in rat models of chemotherapy.
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 broccoli micronutrients

Broccoli isothiocyanates

BITC
BITC has been found to induce cell death in both ER+/PR+ and triple negative breast cancer cells. BITC has also been shown to inhibit self-renewal of breast cancer stem cells and to reduce mammary tumor development in a mouse model of HER2+ breast cancer.
I3C and its metabolic product 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 the proliferation of estrogen receptor positive (ER+) breast cancer cells. I3C/DIM has also been shown to inhibit aromatase (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 demonstrated 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 is the most abundant isothiocyanate derived from consuming broccoli, especially broccoli sprouts. 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 collections of triple negative cells.
In one experiment, mice were implanted with breast cancer tumors and the tumors were treated directly with sulforaphane. 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 dietary intake of carotenoids such as beta-carotene have been reported to have lower risks of breast cancer and its recurrence than those with low intake, although not all studies are in agreement.
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.

Folate

Dietary folate (but not folic acid) intake is associated with reduced breast cancer recurrence risk, especially among women with estrogen receptor negative (ER-) tumors. Co-treatment with progesterone abolished progesterone-induced breast cancer proliferation and migration in one cell study.
However, a 2024 study reported that breast cancer risk increased with higher folate intake in women with the MTHFR C677T (TT) genotype. While this genotype is less common than MTHFR C677T (CC + CT), it suggests that supplementation may be unwise.

Kaempferol

Diets abundant in kaempferol have been found to be associated with reduced breast cancer risk. Kaempferol has been shown to inhibit the growth of ER+/PR+ breast cancer cells, in part through inhibition of glucose uptake. Kaempferol has also been found to inhibit both primary tumor growth and lung metastasis in a mouse model of breast cancer. In addition, kaempferol may protect against the cancer-promoting effects of the endocrine disruptor triclosan, an antibacterial chemical to which most people are routinely exposed.

Additional comments

Broccoli sprouts are better source of isothiocyanates than broccoli

Broccoli sprouts are a superior source of isothiocyanates compared to mature broccoli. One study reported that three-day-old broccoli sprouts had approximately 15 times the level of isothiocyanate-producing glucosinolates than mature broccoli. Generally speaking, broccoli sprouts are safer to eat than other sprouts (for example, alfalfa sprouts, which have been linked to a number of food-borne disease outbreaks due to salmonella and E. coli).

Raw or lightly cooked broccoli is best

Isothiocyanates are obtained from glucosinolates when the enzyme myrosinase is released from damaged plant cells. Myrosinase is physically separate from glucosinolates in intact plant cells. Chewing or chopping a cruciferous vegetable enables the myrosinase to catalyze the reaction that converts its glucosinolates into isothiocyanates. This is part of the plant defense mechanism which is triggered when, for example, an animal chews the plant. The process of conversion to isothiocyanates is halted when cruciferous vegetables are cooked, although human intestinal bacteria facilitate some formation and absorption of isothiocyanates.
Ideally, broccoli and related plants should be consumed raw or chopped and then lightly cooked (by stir-frying, steaming, or microwaving) for a short period of time. Stir frying has been shown to preserve most of the chemopreventive compounds in broccoli, whereas only 14% to 28% of the individual glucosides are retained in the cooked tissue after boiling (most of the remainder being leached into the water).
Similarly, if broccoli is microwaved, it should be done for the shortest period of time and with the least amount of water possible to minimize leaching of phenolic compounds and glucosinolates into water. Even the light blanching used in making frozen broccoli substantially reduces the bioavailability of sulforaphane.

Cruciferous vegetable supplements are not recommended

We recommend consuming broccoli as food and against consuming broccoli pills that have been enhanced to boost the proportion of the presumed key anti-cancer chemicals in broccoli. Unlike some plant-based chemopreventive compounds, meaningful amounts of sulforaphane and other isothiocyanates can be obtained from food. There is some evidence that concentrated cruciferous vegetable extracts can act as estrogen agonists and promote breast cancer cell proliferation. One study reported that while physiologically achievable doses of I3C reduced aromatase expression of ER+/PR+ breast cancer cells, higher doses induced its expression.
In addition, the anticancer properties of broccoli 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.

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 broccoli.