CRUCIFEROUS VEGETABLES & CANCER PREVENTION*
Edible plants in the Brassica family (also called Cruciferae) are termed Cruciferous Vegetables. They are widely considered to be healthful foods. They are high in vitamin C and soluble fibre and they also contain multiple nutrients with potent anti-cancer properties.
Extensive selective breeding has produced a large number of variants, especially within the genus Brassica. The following is a list of some of the common cruciferous vegetables.
Genus Brassica, species oleracea:
Genus Brassica, species rapa:
Turnip root, greens
Genus Brassica, species hirta:
Mustard seeds, white
Genus Brassica, species nigra:
Mustard seeds, black
Cruciferous vegetables are one of the dominant food crops world-wide.
Cruciferous Vegetables and Cancer Prevention
Cancer is one of the leading causes of death in developed countries. Diet is a causative factor in this (refer to my March 2008 newsletter ‘Cancer Prevention’). Epidemiological studies have shown that a diet rich in cruciferous vegetables is protective against many cancers.
Dietetic professionals recommend an increase in fruit and vegetable intake to reduce the incidence of cancer. Among the reasons cited for this health benefit are that fruit and vegetables are excellent sources of fibre, vitamins and minerals. They also contain non-nutritive components that may provide substantial health benefits beyond basic nutrition. The epidemiological studies referred to above provide evidence that the consumption of cruciferous vegetables protects against cancer more effectively than just fruits and vegetables.
Non-nutritive Components of Cruciferous Vegetables
Cruciferous vegetables such as Brussels sprouts, broccoli, cabbage, cauliflower and the seeds of mustard (especially black) contain many phytochemicals (chemicals naturally present in plants) including sulforaphane, sinigrin and selenium.
Sulforaphane is a sulphur-containing isothiocyanate derivative.
It is an anticancer, antidiabetic and antimicrobial compound that can be obtained by eating cruciferous vegetables. It occurs in these vegetables as sulforaphane glucosinolate. The sulforaphane is released upon damage to the plant (such as from chewing), and thus is available after ingestion.
Within hours of ingestion it enters the bloodstream where it circulates widely to trigger the immune system response to carcinogens. This is achieved by inducing a series of proteins termed phase 2 detoxification enzymes which are enzymes of cancer defence. They act as scavengers for cancer-causing molecules before they can damage DNA and promote cancer. A study by Dr James Brooks & co-workers has shown that sulforaphane induces phase 2 enzyme expression and activity in human prostate cells. This study helps to explain the lower prostate cancer risk with men who consume more cruciferous vegetables.
Sulforaphane and another compound from Brassica vegetables, diindolylmethane, have recently been shown to synergise together in the inhibition of cancer growth.
Sulforaphane is also an antioxidant and thus protects against free radical damage of DNA (which is linked to the development of cancer).
Oestrogen metabolism is also altered by sulforaphane which, as well as the above properties, may explain the reduced risk of breast cancer linked to the ingestion of this naturally occurring chemical.
Sulforaphane also inhibits extracellular, intracellular and antibiotic-resistant strains of Helicobacter pylori (the cause of some peptic ulcers).
When applied topically, sulforaphane seems to protect skin against UV radiation damage, and thus potentially against cancer.
The highest levels of sulforaphane are found in broccoli sprouts. In one experimental study, three-day-old broccoli sprout extracts were fed to groups of rats exposed to a powerful carcinogen, dimethlybenzanthracene. The rats that received the extract, compared to those which did not receive the extract, developed fewer tumours, and those tumours that did grow on treated rats had smaller size and extended
development times. Subsequent studies have determined that broccoli sprouts contain 20 to 50 times the amount of chaemo-protective phytochemicals found in mature broccoli heads.
Sinigrin is a glucosinolate which belongs to the family of glucosides that are found in some plants of the Brassica family including broccoli, Brussels sprouts, horseradish and the seeds of black mustard. Whenever sinigrin-containing plant tissue is crushed or otherwise damaged, the enzyme myrosinase degrades sinigrin to a mustard oil (allyl isothiocyanate) which gives the pungent taste of black mustard seeds and horseradish. Seeds of white mustard give a much less pungent mustard because this species contains a different glocosinolate, sinalbin. Ironically it is this breakdown product of sinigrin that makes so many people hate the taste and smell of Brussels sprouts, the “little cabbages”.
Research has shown that sinigrin may destroy pre-cancerous cells, causing them to disintegrate (apoptosis). Agricultural researchers have developed a sweeter-tasting Brussels sprout. Sweeter sprouts mean less sinigrin, and less sinigrin means less protection against cancer.
Glycosinolates protect against breast, lung, prostate and colon cancers.
Selenium is a potent antioxidant. It is a mineral, a trace element which the plants assimilate from the soil. The amount present in a plant is determined by the levels in the soil.
Broccoli and other cruciferous vegetables accumulate the mineral selenium and clinical trials have demonstrated that selenium may decrease the incidence of prostate and lung cancers. Animal studies have shown that selenium and sulforaphane interact in the animal that consumes broccoli to protect against oxidative stress in the cell via the antioxidant enzyme thioredoxin reductase. Independent of this, as a potent antioxidant, selenium is protective against cancer.
Kale, an Excellent Cruciferous Vegetable
In the many lists of the beneficial cruciferous vegetables, as set out by different authors, kale is usually indicated to be one of the most important.
Kale is a form of cabbage (Brassica oleracea). It is green in colour and the central leaves do not form a head. As set out above, the species Brassica oleracea contains a wide array of vegetables.
Kale is the most robust cabbage type - indeed it is said that the hardiness of kale is unmatched by any other vegetable. It rarely suffers from pests and diseases of other members of the cabbage family.
Kale is considered to be a highly nutritious vegetable with powerful antioxidant properties and it is also anti-inflammatory. It is rich in sulforaphane. It is also very high in beta carotene, vitamin C, lutein, zeaxanthin and reasonably rich in calcium. It is also a good source of iron and carotenoids (which provide vitamin A).
Because it has a high vitamin K content, patients taking anti-coagulants such as warfarin (which acts to lower vitamin K) are encouraged to avoid this food.
There are many different leaf varieties. A google image search ‘Kale’ will show pictures of a large number of different types of kale.
Broccoli Sprouts, and How to Grow Them
Broccoli sprouts are the most nutritious of all the cruciferous vegetables.
‘How to sprout’ is essentially straight forward. After soaking for 12 to 24 hours, drain off the water and then rinse thoroughly, and repeat until the water is clear. Leave the seeds to sprout (in a suitable covered jar in a dark place), rinsing morning and evening. Once sprouted, after the final rinse, allow the seeds to drain, dry off excess water by shaking them in a tea towel and place in a container with a lid in the refrigerator. The sprouts will last for at least a week. They will continue to grow (although at a much slower rate) in the fridge.
Broccoli takes about 6 to 8 days to grow to the ‘two leaf’ stage ready for eating. During the last two days of sprouting, the seeds should be left in daylight (not direct sunlight) to allow photosynthesis to take place.
Broccoli seed can be purchased from some health food shops and most food co-ops. Unfortunately, it is expensive. Wholesale price varies from A$120 to $200 per kilo. Retail price is in the region of $8 for 20gm (ie $400 per kilo). Within Australia, contact Alison at ‘Rainbow Sprouts’ on 02-9913-3559.
A Word of Caution
Cruciferous vegetables contain goitrogens. These are substances that cause enlargement of the thyroid gland, called a goitre. Cooking for 30 minutes significantly reduces the amount of goitrogens. Goitrogens inhibit the incorporation of iodine into the thyroid hormone, and the thyroid gland compensates by enlarging. Thyroid function should be monitored if there is prolonged high consumption of these vegetables.
Drs. G. Murillo and R. Mehta in their article ‘Cruciferous Vegetables and Cancer Prevention’ published in ‘Nutrition and Cancer’ volume 41, September 2001, summarised the published experimental carcinogenesis studies as well as clinical trials and studies on the mechanism of action of the ‘chemopreventive’ agents in the cruciferous vegetables. Their conclusion was:
“Results clearly point toward a positive correlation between cancer prevention of many target organs and consumption of cruciferous vegetables or their active constituents.”
*Copyright 2008: The Huntly Centre.
Disclaimer: All material in the huntlycentre.com.au website is provided for informational or educational purposes only. Consult a health professional regarding the applicability of any opinions or recommendations expressed herein, with respect to your symptoms or medical condition.
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