By greens, we mean leafy cruciferous vegetables such as collard greens, mustard greens, turnip greens, and arugula, but not kale. Greens have been shown to have antioxidant and anti-inflammatory properties, improve glucose metabolism and be cardioprotective. Greens are the source of a variety of chemopreventive compounds.
For example, greens are a good dietary source of chemopreventive isothiocyanates, including allyl isothiocyanate (AITC), benzyl isothiocyanate (BITC), indole-3-carbinol (I3C) and its metabolic product 3,3'-diindolylmethane (DIM), and sulforaphane. Arugula is a good source of the isothiocyanate erucin.
Greens also contain significant amounts of the carotenoids beta-carotene and lutein, as well as kaempferol, all of which have been reported to have anti-cancer properties. In addition, greens are a good dietary source of vitamin K, folate, and vitamin C, as well as manganese and various other minerals.

Breast cancer-related effects of eating greens

Consumption of greens is associated with reduced breast cancer risk. Greens are the source of a variety of compounds with anti-cancer activities. Components of greens have been found to down-regulate hormone receptor expression, promote apoptosis, suppress cell cycle progression and inhibit angiogenesis of human breast cancer cells. Greens can increase the beneficial effects of some breast cancer treatments. Stewing greens reduces their potential chemopreventive properties.

Epidemiological studies

A number of population studies have reported that consumption of one or more cruciferous vegetables is associated with lower risk of breast cancer. For example, one study based on Italian and Swiss populations found 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 such vegetables. Another study of African-American women found that those with high cruciferous vegetable consumption (often including greens) had a lower risk of hormone receptor negative (ER-/PR-) breast cancer.

Greens can increase treatment effectiveness

DIM, I3C and lutein have been shown to enhance the therapeutic efficacy of the chemotherapy drugsAdriamycin (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.
Greens 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.
AITC has been reported to reduce Adriamycin-induced heart damage (cardiomyopathy) in a rat model of chemotherapy.
Beta-carotene enhanced 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.
Kaempferol has also been shown to reduce the degree of heart damage caused by Adriamycin in a rat model 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 micronutrients in greens

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. 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.
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.
Erucin
Erucin is more present in arugula than other greens. Erucin has been shown to inhibit the growth and proliferation of ER+/PR+ breast cancer cells.
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 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.

Carotenoids

Women with substantial intake of carotenoids such as beta-carotene and lutein 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.
Beta-carotene
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.
Lutein
Lutein consumption and circulating lutein levels have also been found to be associated with reduced risk of breast cancer in several epidemiological studies. Lutein has been shown to inhibit the progression of both ER+/PR+ and triple negative breast cancer cells under hypoxia, a low-oxygen condition in which solid breast tumors can thrive.

Kaempferol

Arugula and mustard greens are good sources of the flavonol kaempferol. Turnip greens are a lesser source. 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 triclosan, an antibacterial chemical to which most people are routinely exposed which is an endocrine disruptor.

Folate

Dietary folate (but not folic acid) intake is associated with reduced risk of breast cancer recurrence, 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.

Additional comments

Collard greens, mustard greens and turnip greens are most beneficial when prepared without stewing for long periods of time, which can cause a 60% loss of isothiocyanates. The best methods are chopping followed by steaming, pressure-cooking, microwaving in a small amount of water, or quickly stir-frying. Non-organic greens must be washed very thoroughly to remove pesticide residue.
The term Asian greens refers to a mixture of both cruciferous and non-cruciferous leafy green vegetables which can include bok choy, Chinese broccoli, Chinese celery, Chinese mustard greens, Chinese oil vegetable, chrysanthemum greens, daikon greens, Malabar spinach, napa cabbage, pea shoots, or water spinach.
Some cruciferous vegetables, including collard greens (but not turnip greens), 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 more complete list, including less recent studies, please click on greens.