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Broccoli

Other common name(s): none

Scientific/medical name(s): Brassica oleracea italica

Description

Broccoli is a cruciferous vegetable that belongs to the cabbage family, which also includes arugula, cauliflower, collards, bok choy, kale, mustard greens, radishes, turnips, watercress, rutabaga, and brussels sprouts. It is identified by its dense clusters of green flower buds.

Overview

Broccoli contains certain chemicals that may reduce the risk of colorectal or other cancers, although it is not clear which individual compounds may be responsible for the protective effects. While research in this area continues, the best advice at this time to reduce cancer risk is to eat a wide variety of vegetables. It is reasonable to include broccoli as part of a balanced diet.

How is it promoted for use?

Broccoli is considered a good source of nutrients because it is rich in vitamin C, carotenoids (vitamin A-like substances), fiber, calcium, and folate. Broccoli is also a source of many substances called phytochemicals, or plant chemicals, that may have anticancer properties. For example, broccoli contains several compounds called isothiocyanates, including sulforaphane and indole-3-carbinol (I3C), which have been touted as possible anti-cancer agents in recent years. Early studies have shown these substances may act as anti-oxidants and may boost detoxifying enzymes in the body. Some studies have also suggested they may alter the levels of estrogen in the body, which might affect breast cancer risk.

The chemical composition of broccoli and other cruciferous vegetables is complex, which makes it hard to determine which compound or combination of compounds may provide protection against cancer. Eating a wide variety of plant-based foods may be the best way to get the necessary components.

Some researchers suggest that small amounts of broccoli sprouts may protect against the risk of cancer as effectively as much larger amounts of the mature vegetable. We are not aware of any clinical studies that have been done in humans to verify this claim.

What does it involve?

Broccoli can be eaten raw or cooked in a variety of ways. It can be purchased fresh or frozen in most grocery and organic food stores. Broccoli retains the most nutrients when eaten raw. Cooking reduces some of the benefits of broccoli because the heating process seems to destroy some anti-cancer compounds.

Some chemicals found in broccoli, such as indole-3-carbinol, are also available in pill form as dietary supplements.

What is the history behind it?

Broccoli has been around for more than 2,000 years but has only been commercially grown in the United States since the 1920s. Today, more than 90% of the broccoli harvested in the United States comes from California, although it is also grown in other parts of the country.

About 2 decades ago, researchers first suggested a possible link between diets high in cruciferous vegetables (a group of plants including cauliflower, cabbage, broccoli, and Brussels sprouts)) and a lower risk of cancer. However, it was not until the 1990s that certain chemicals found in broccoli were identified as possible cancer-preventing compounds. In 1997, a study was published that noted broccoli sprouts had higher levels of one of these compounds than mature broccoli.

What is the evidence?

Diets high in cruciferous vegetables appear to be linked with a lower risk of certain types of cancer. A population-based study found that those who ate diets high in lutein, a vitamin A–like chemical obtained from vegetables such as broccoli, spinach, and lettuce, had fewer cases of colon cancer. A similar study suggested that those who ate cruciferous vegetables seemed to have a lower risk for bladder cancer, but a similar study of smokers found no such benefit. Recent studies suggest that the effect of broccoli and related cruciferous vegetables on cancer risk may partly depend on an inherited variation in certain metabolic enzymes. For example, when people with certain glutathione S-transferase types eat a diet high in cruciferous vegetables, their risk for lung cancer is lower. Randomized clinical trials are needed to clarify these results.

Laboratory and animal studies have suggested that certain compounds in broccoli may have anti-cancer properties. These types of studies can suggest possible helpful effects, but they do not provide proof that such effects can be achieved in humans. Further studies are needed to find out whether possible anticancer properties could benefit humans. Some research has suggested that sulforaphane, a substance that is present at much higher levels in broccoli sprouts than in the mature vegetable, may be a powerful cancer-preventing agent. Some researchers have suggested that eating small amounts of broccoli sprouts may protect against the risk of cancer as effectively as much larger amounts of the mature vegetable. We are not aware of any clinical studies that have been done in humans to verify this claim. Sulforaphane is thought to prompt the body to make higher levels of enzymes that protect against cancer-causing chemicals. One study showed that breast tumor development was significantly reduced in laboratory animals that ate sulforaphane. Other laboratory studies have shown that sulforaphane may help protect against prostate, colon, pancreas, and other types of cancer. Some studies have also suggested that the compound may help treat some types of cancer. More research in animals and humans will be needed to confirm these findings.

Another substance in broccoli, indole-3-carbinol (I3C), seems to alter estrogen levels and may also raise levels of protective enzymes in the body. Several studies of cancer cells growing in laboratory dishes or flasks have shown it may slow or stop the growth of breast, prostate, and other cancer cells. Some early studies in animals have shown similar results. Small studies in humans have found it may prevent the development of pre-cancerous growths in the cervix, as well as growths called papillomas in the throat. Again, larger studies are needed to find out what benefits I3C may have against cancer.

Scientists caution that while broccoli appears promising as an excellent food for preventing cancer, the results of such studies cannot be considered by themselves. The anti-cancer effects of any single food cannot be completely understood without looking at it as part of a bigger dietary picture. It is still unclear, for example, whether the phytochemicals in broccoli have benefit on their own or whether it is the vitamin C, beta carotene, folate, and other compounds, working together and in the right quantities, that might protect people against cancer.

A balanced diet that includes 5 or more servings a day of fruits and vegetables along with foods from a variety of other plant sources such as nuts, seeds, whole grain cereals, and beans is likely to be more healthful than eating large amounts of one food.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike drugs (which must be tested before being allowed to be sold), the companies that make supplements are not required to prove to the Food and Drug Administration that their supplements are safe or effective, as long as they don't claim the supplements can prevent, treat, or cure any specific disease.

Some such products may not contain the amount of the herb or substance that is written on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand.

Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

Broccoli and broccoli sprouts are generally safe to eat. Since broccoli is high in fiber, eating large amounts of it may cause gas. High-fiber foods should be reduced or avoided in people with diarrhea and some other colon problems. Raw broccoli may be more likely to cause irritation, especially in those with certain bowel conditions. Relying on this type of diet alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Additional resources

More information from your American Cancer Society

The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).

Dietary Supplements: What Is Safe?

The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

Complementary and Alternative Methods and Cancer

Placebo Effect

Learning About New Ways to Treat Cancer

Learning About New Ways to Prevent Cancer

References

Bell MC, Crowley-Nowick P, Bradlow HL, et al. Placebo-controlled trial of indole-3-carbinol in the treatment of CIN. Gynecol Oncol. 2000;78:123-129.

Brennan P, Hsu CC, Moullan N, et al. Effect of cruciferous vegetables on lung cancer in patients stratified by genetic status: a mendelian randomisation approach. Lancet.2005;366:1558-1560.

Cao G, Booth SL, Sadowski JA, Prior RL. Increases in human plasma antioxidant capacity after consumption of controlled diets high in fruit and vegetables. Am J Clin Nutr. 1998;68:1081-1087.

Cover CM, Hsieh SJ, Tran SH, et al. Indole-3-carbinol inhibits the expression of cyclin-dependent kinase-6 and induces a G1cell cycle arrest of human breast cancer cells independent of estrogen receptor signaling. J Biol Chem. 1998;273:3838-3847.

Fahey JW, Zhang Y, Talalay P. Broccoli sprouts: an exceptionally rich source of inducers of enzymes that protect against chemical carcinogens. Proc Natl Acad Sci USA.1997;94:10367-10372.

Michaud DS, Pietinen P, Taylor PR, Virtanen M, Virtamo J, Albanes D. Intakes of fruits and vegetables, carotenoids and vitamins A, E, C in relation to the risk of bladder cancer in the ATBC cohort study. Br J Cancer. 2002;87:960-965.

Michaud DS, Spiegelman D, Clinton SK, Rimm EB, Willett WC, Giovannucci EL. Fruit and vegetable intake and incidence of bladder cancer in a male prospective cohort. J Natl Cancer Inst. 1999;91:605-613.

Nestle M. Broccoli sprouts in cancer prevention. Nutr Rev. 1998;56:127-130.

Parnaud G, Li P, Cassar G, et al. Mechanism of sulforaphane-induced cell cycle arrest and apoptosis in human colon cancer cells. Nutr Cancer. 2004;48:198-206.

Parnaud G, Li P, Cassar G, Rouimi P, Tulliez J, Combaret L, Gamet-Payrastre L. Mechanism of sulforaphane-induced cell cycle arrest and apoptosis in human colon cancer cells. Nutr Cancer. 2004;48:198-206.

PDRhealth. Indole-3-Carbinol. Accessed at: www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/ind_0315.shtml on Accessed June 10, 2008.

PDRhealth. Sulforaphane. Accessed at: www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/sul_0243.shtml on June 12, 2007. Content no longer available.

Shapiro TA, Fahey JW, Wade KL, Stephenson KK, Talalay P. Human metabolism and excretion of cancer chemoprotective glucosinolates and isothiocyanates of cruciferous vegetables. Cancer Epidemiol Biomarkers Prev. 1998;7:1091-1100.

Shapiro TA, Fahey JW, Dinkova-Kostova AT, et al. Safety, tolerance, and metabolism of broccoli sprout glucosinolates and isothiocyanates: a clinical phase I study. Nutrition & Cancer. 2006;55:53-62.

Singh SV, Srivastava SK, Choi S, et al. Sulforaphane-induced cell death in human prostate cancer cells is initiated by reactive oxygen species. J Biol Chem. 2005;280:19911-19924.

Slattery ML, Benson J, Curtin K, Ma KN, Schaeffer D, Potter JD. Carotenoids and colon cancer. Am J Clin Nutr. 2000;71:575-582.

Tang L, Zhang Y, Jobson HE, et al. Potent activation of mitochondria-mediated apoptosis and arrest in S and M phases of cancer cells by a broccoli sprout extract. Molecular Cancer Therapeutics.2006;5:935-944.

Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.

Last Medical Review: 11/01/2008
Last Revised: 11/01/2008