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Health Benefits of Cruciferous Vegetables

Pennington Biomedical Research Center

Heli Roy, PhD Shanna Lundy, BS

Phillip Brantley, PhD, Director

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The cruciferae are the family of plants that include the various familiar members of the species Brassica oleracea.

Examples include: Broccoli, cabbage, cauliflower, kale, Brussels sprouts in the US.

Other examples widely consumed outside of the US include: Oriental cabbage, arugula, watercress, radish, daikon, wassabi, and various mustards.

Cruciferous vegetables:What are they?

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A striking and characteristic chemical property of cruciferous plants is their high content of glucosinolates.

Glucosinolates and their isothiocyanate hydrolysis (breakdown) products are well-known protectors against carcinogenesis, suggesting that greater intakes of these vegetables may lower the risk of several types of cancer.

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The Unusual Phytochemistry of Crucifers

Glucosinolates are the precursors of isothiocyanates (mustard oils). Glucosinolates play protective and evolutionarily important roles in

plants, including: Allelopathy

Suppression of growth of neighboring plants Specific positive and negative feeding cues

For some insects Broad antibiotic properties

Including nematocidal, antimicrobial, antifungal, antiprotozoal, and insecticidal activities

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When food is prepared or chewed, or in response to plant injury by predators, the enzyme myrosinase which accompanies the glucosinolates is released.

This is the enzyme responsible for hydrolyzing glucosinolates to isothiocynates.

In the absence of myrosinase (when food is cooked and myrosinase is heat inactivated), humans have the ability to efficiently convert glucosinolates to isothiocynates through the action of microflora in the GI tract. Cabbage worm

In humans?

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Overview

Conversion of Glucosinolates to Isothiocyanates by Plant Myrosinase.

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Overview At least 120 chemically distinct glucosinolates have

been identified in plants.. Although the majority have been isolated from

crucifers, 15 other families of plants are known to contain glucosinolates.

The other families do include many edible species; however, they are uncommon to the Western world and are thought to contribute little to our diets.

Although only few attempts have been made to assess human glucosinolate consumption, some estimates are as high as 300 mg/d (~660 µmol/d).

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Chemoprotective effects of isothiocyanates and glucosinolates Since the early 1960s, both natural and synthetic

isothiocyanates have attracted considerable and growing attention as important and effective protectors against chemical carcinogenesis in a number of animal models.

Even though only a few glucosinolates have been examined (largely because adequate quantities of these compounds have been unavailable), some appear to be very effective in inhibiting carcinogenesis.

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History The history of these developments can be traced

from the comprehensive review by Hecht and colleagues in which their work involved the NNK, which is probably the most prominent carcinogen derived from cigarettes..

Several isothiocyanates inhibit the action of this carcinogen (NNK) through inhibition of its metabolism.

Hecht, SS. Chemoprevention of Cancer by Isothiocyanates, Modifiers of Carcinogen Metabolism. J. Nutr. 129: 768S–774S, 1999.

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Evidence

Of the inverse association between crucifer consumption and cancer

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Bladder Cancer Michaud and colleagues analyzed 252 cases of bladder cancer that

developed in 47,909 health professionals during a 10-y period.

No significant associations were found bladder cancer and the consumption of:

Total fruits and vegetables Fruits only Vegetables only Or yellow or green leafy vegetables

However, the multivariate risk reduction (RR) ratio for cruciferous vegetables was highly significant.Michaud DS, et al. Fruit and vegetable intake and incidence of bladder cancer in a male prospective cohort. J Natl Cancer Institute 91(7): 605-613, 1999.

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Fruit and vegetable intake and incidence of bladder cancer in a male prospective cohort

Relative Risk P-value

Fruits and vegetables 0.75 0.25

Fruits 1.12 0.68

Vegetables 0.72 0.09

Yellow vegetables 1.01 0.50

Green leafy vegetables 0.99 0.81

Cruciferous vegetables 0.49 0.008

* The only significant reduction in relative risk was observed with cruciferous vegetables.

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In the Health Professionals Follow-up Study, bladder cancer was only weakly associated with low intake of fruits and vegetables, but high intake (5 or more servings/week versus 1 or less servings/week) of cruciferous vegetables was associated with a statistically significant 51% decrease in bladder cancer.

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Cohen et al. examined the relationship between fruit and vegetable consumption and prostate cancer incidence in men <65 y of age.

High fruit consumption showed no effect on prostate cancer incidence. High overall vegetable consumption was associated with reduced risk. However, cruciferous vegetables were clearly protective when risk was

adjusted for total vegetable consumption and other variables.

Prostate cancer

Cohen JH et al. Fruit and vegetable intakes and prostate cancer. J Natl Cancer Institute 92(1): 61-68, 2000.

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Also, prostate cancer risk was found to be reduced by cruciferous vegetable consumption in a population-based case-control study carried out in western Washington state.

Three or more servings per week, compared to less than one serving of cruciferous vegetables per week resulted in a statistically significant 41% decrease in prostate cancer risk.

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Breast cancer and non-Hodgkin’s lymphoma

A case-controlled study in China found that intake of cruciferous vegetables, measured by urinary secretion of isothiocyanates, was inversely related to the risk of breast cancer. The quartile with the highest intake had only 50%

of the risk of the lowest intake group

In the Nurses’ Health Study, a high intake of cruciferous vegetables (5 or more servings/week versus less than two servings/week) was associated with a 33% lower risk of non-Hodgkin’s lymphoma.

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Conclusions… There is much evidence in regards to cruciferous

vegetables and their role in the now widely recognized protective effects of vegetables against the risk of cancer.

Much research has been done on the unusual phytochemicals known as glucosinolates found in cruciferous vegetables and their hydrolysis products, the isothiocyanates.

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Conclusions… The isothiocyanates have already been established as playing a role in

modulating the activities of enzymes involved in the metabolism of carcinogens, especially by the induction of phase 2 detoxification enzymes.

With time, a better understanding of the dynamic role that fruits and vegetables, in particular the cruciferous vegetables play in health and disease, will be uncovered.

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References Donaldson M. Nutrition Journal. 2004. Nutrition and cancer: a review of the

evidence for an anti-cancer diet. - Talalay P, Fahey J. Phytochemicals from cruciferous plants protect against

cancer by modulating carcinogen metabolism. Journal of Nutrition. 2001. Hecht, SS. Chemoprevention of Cancer by Isothiocyanates, Modifiers of

Carcinogen Metabolism. J. Nutr. 129: 768S–774S, 1999. Michaud DS, et al. Fruit and vegetable intake and incidence of bladder cancer

in a male prospective cohort. J Natl Cancer Institute 91(7): 605-613, 1999. Cohen JH et al. Fruit and vegetable intakes and prostate cancer. J Natl

Cancer Institute 92(1): 61-68, 2000.