Patient handout for Kale
Kale
Kale
SCIENTIFIC NAME
Brassica oleracea, Brassica oleracea var. viridis, synonym Brassica oleracea var. acephala
FAMILY
Brassicaceae/Cruciferae.

CAUTION: See separate listing for Broccoli, Brussel Sprouts, Cabbage, Cauliflower, and Collard.

+ Other Common Names

  • Boerenkool, Borecole, Chou Fourrager, Chou Kale, Col rizada, Kale Frisé, Kale Frisé Sibérien, Kale Leaf, Kale Noir, Kale Rouge de Russie, Winter Greens.

Overview

Kale is a dark, leafy vegetable that has green or purple leaves (90482,90485). It is similar to cruciferous vegetables such as broccoli, cauliflower, and collard (90480). It is believed to have originated in the eastern Mediterranean and to have been used as a food crop since 2000 BC (90482). There is interest in its use as an antioxidant and for improving overall health.

Safety

LIKELY SAFE ...when used in amounts commonly found in foods.

There is insufficient reliable information available about the safety of kale when used orally in medicinal amounts.

PREGNANCY AND LACTATION: LIKELY SAFE ...when used orally in amounts commonly found in foods. There is insufficient reliable information available about the safety of kale when used orally in medicinal amounts; avoid use.

+ Adverse Effects

General: Orally, kale is generally well tolerated when consumed in amounts commonly found in foods. No adverse effects have been reported with medicinal use. However, a thorough evaluation of safety outcomes has not been conducted.

+ Effectiveness

INSUFFICIENT RELIABLE EVIDENCE to RATE
Bladder cancer. It is unclear if consuming kale in the diet can reduce the risk of bladder cancer.
+ Details:  Population research suggests that patients with bladder cancer consumed approximately 0.18 fewer cups of cruciferous vegetables, such as cabbage, Brussels sprout, cauliflower, broccoli, kale, or collards, on a weekly basis in the year prior to diagnosis when compared with people without bladder cancer. The effects of kale, specifically, are unclear (14864). Other population research suggests that eating at least five servings per week of cruciferous vegetables, such as cauliflower, Brussels sprout, cabbage, broccoli, and kale, is associated with a 51% reduction in the risk of developing bladder cancer in males when compared with eating up to one serving per week. However, higher intake of kale alone does not seem to be associated with a reduced risk of bladder cancer (26184).
Breast cancer. It is unclear if consuming kale in the diet can reduce the risk of breast cancer.
+ Details:  Population research suggests that the highest dietary intake of cruciferous vegetables, including broccoli, Brussels sprout, cabbage, cauliflower, collards, and kale, is associated with a slight increase in the risk of breast cancer in premenopausal adults when compared with the lowest intake. In postmenopausal adults, the highest intake appears to be associated with a statistically insignificant reduced risk of breast cancer (26188). It is not clear if kale played any role in these findings.
Inflammatory bowel disease (IBD). Although there is interest in oral kale for IBD, there is insufficient reliable information available about the use of kale for this purpose.

Menopausal symptoms. Although there is interest in oral kale for reducing menopausal symptoms, there is insufficient reliable information available about the use of kale for this purpose.

More evidence is needed to rate kale for these uses.

Dosing & Administration

  • Adult

    Oral:

    Research is limited; typical dosing is unavailable.
  • Standardization & Formulation

    There is insufficient reliable information available about the standardization of kale.

Interactions with Drugs

None known.

Interactions with Supplements

None known.

Interactions with Conditions

None known.

Interactions with Lab Tests

None known.

Overdose

There is insufficient reliable information available about the presentation or treatment of overdose with kale.

Commercial Products Containing: Kale


Pharmacokinetics

There is insufficient reliable information available about the pharmacokinetics of kale.

Mechanism of Action

General: The applicable parts of kale are the above ground parts. Kale contains carotenoids (including lutein and beta-carotene), vitamin K (phylloquinone), vitamin C, vitamin A, folate, iron, calcium, magnesium, phosphorus, and potassium. It also contains glucosinolates including ascorbigen, terpenoids, indole derivatives, and flavonoid glycosides of quercetin, kaempferol, and isorhamnetin (6790,26497,90480,90483,90484,109905).

Anti-cancer effects: Epidemiological research suggests that cruciferous vegetables such as kale have protective effects against some types of cancer (14145). These vegetables contain about 10 different kinds of glucosinolates (6790). Glucosinolates are usually accompanied by myrosinase, a thioglucosidase enzyme found in plant cells in separate compartments (6792). When the plant cells are damaged by cutting or chewing, the myrosinase is exposed to glucosinolates, catalyzing its hydrolysis to a range of breakdown products, such as indoles, nitriles, and isothiocyanates (ITCs).

ITCs are sulfur-containing phytochemicals present in the form of sulforaphane (SFN), phenylethylisothiocyanate, benzylisothiocyanate, and 3-phenylpropylisothiocyanate. These chemicals are thought to be anticarcinogenic due to their effects on phase I and phase II enzymes (10264,26449,26483,47627,55547). Phase I and phase II enzymes act as the body's first line of defense against cancer by protecting the body from carcinogens that routinely enter the body through the diet and the environment. ITCs generally enhance the activity of phase II enzymes and inhibit phase I enzymes, thus reducing the production of electrophilic intermediates with carcinogenic activity and enhancing the detoxification and clearance of carcinogens. ITCs also act as suppressing agents during the promotion phase of the neoplastic process and induce apoptosis, thereby inhibiting cell growth (26449,26485).

Other products of glucosinolate hydrolysis, indoles, include indole-3-acetonitrile, indole-3-carbinol (I3C), and 3,3'-diindolylmethane (DIM) (47627). Evidence from in vitro research suggests that I3C inhibits carcinogenesis by inducing enzymes such as cytochrome P450-dependent monooxygenases, glutathione S-transferases (GST), or epoxide hydrolases (EH). These enzymes metabolize carcinogens to more polar and excretable forms (26489,26491,47596). Evidence from animal research has shown that indoles and isothiocyanates attenuate the effects of polycyclic aromatic hydrocarbons (PAHs) and nitrosamines and are protective towards heterocyclic amines (51183). The effects on PAH and nitrosamines appear to be via induction of GST and inhibition of cytochrome P450 isoenzymes, respectively.

Indoles and phytoestrogens found in Brassica species may also contribute to the protection of hormone-dependent breast and cervical cancers. Evidence from animal research suggests that I3C inhibits mammary cancers (26469) and that its use may inhibit breast and cervical cancers in women (47627). In women, I3C increases the 2-hydroxylation of estrogen urinary metabolites (47615). Evidence from in vitro research suggests that I3C suppresses the proliferation of various tumor cells, including breast, prostate, endometrial, colon, and leukemic cells (47627).

Metabolic effects: Research in obese animals shows that adding 9% kale to a high -fat diet (45% fat) for 12 weeks lowers serum triglycerides and low-density lipoprotein (LDL) cholesterol levels when compared with the high- fat diet alone. Kale contains compounds which act as bile acid sequestrants, preventing bile acid recirculation and reducing fat absorption. Adding kale to a high -fat diet also prevents increases in endotoxemia and inflammation, but does not reduce body weight, fat accumulation, or insulin resistance when compared with the high- fat diet alone. In adipose tissue, kale increases the expression of genes involved in adipogenesis, downregulates expression of adipose tissue-specific inflammation markers, and reduces gene expression of several chemokines and chemokine receptors (109905).

References

See Monograph References


Monographs are reviewed on a regular schedule. See our Editorial Principles and Process for details. The literature evaluated in this monograph is current through 9/18/2023. This monograph was last modified on 1/23/2023. If you have comments or suggestions, please tell the editors.