Kale has the highest levels of vitamins of all cruciferous vegetables (a vegetable group that also includes broccoli, cabbage, cauliflower, collard greens and brussels sprouts). Kale has been shown to have antioxidant, antigenotoxic, anti-inflammatory and antimicrobial properties, and to be cardioprotective. Kale contains significant levels of vitamin C and vitamin K. Kale is also a very good source of beta-carotene, lutein, quercetin, kaempferol, indole-3-carbinol (I3C), 3,3'-diindolylmethane (DIM), and sulforaphane, as well as sinigrin and other glucosinolate hydrolysis products, most of which have been reported to have anti-cancer properties.
Kale and cruciferous vegetables as a group have been shown to inhibit the growth of human pancreatic cancer cells and to reduce the risk of occurrence of lung, gallbladder, bladder, prostate, ovarian and colorectal cancer.
Breast cancer-related effects of eating kale
Components of kale have been found to down-regulate hormone receptor expression, promote apoptosis, suppress cell cycle progression and inhibit angiogenesis of human breast cancer cells. Consumption of brassica vegetables has been shown to reduce the estrogen metabolite 16alpha-hydroxyestrone, which is a breast cancer promoter.
Kale has been reported to be associated with reduced breast cancer risk in population studies. A Korean study found an association between kale consumption and lower incidence of breast cancer. A large U.S. 2016 prospective study reported that women with high kale intake in early adulthood had reduced risk of breast cancer in middle age and later years.
Kale components quercetin and I3C have been shown increase the anti-cancer effects of the chemotherapy drug Taxol (paclitaxel).
Kale is healthiest when prepared by steaming and not by stir-frying. Non-organic kale must be washed very thoroughly to remove pesticide residue.
We recommend consuming kale and other cruciferous vegetables as food and against consuming components of them as pills (e.g. DIM pills). There is some evidence that concentrated cruciferous vegetable extracts can act as estrogen agonists and promote breast cancer cell proliferation. Also, the anticancer properties of kale 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 Russian kale, but not most kale sold in the U.S., contain thioglucoside compounds in sufficient amounts to potentially interfere with the formation ofthyroid hormone in women with iodine deficiency.
Below are links to recent studies concerning this food. For a more complete list, including less recent studies, please click on kale.