Broccoli and cousins are powerful cancer fighters
Protective effects against prostate, lung cancers
The elder George Bush went public about hating broccoli and proclaimed that because he was president, he didn’t have to eat it. Whatever you think of the elder Bush’s politics, his anti-broccoli pronouncements were far from sound health policy. In fact, there is growing evidence that broccoli and other cruciferous vegetables offer a wealth of health benefits not found anywhere else in the plant kingdom.
All health care providers know that vegetables are essential to good health, and researchers say the more veggies consumed, the greater the protection against cancer and heart disease. But recent research shows that broccoli and its fellow members of the nutrient-packed cruciferous vegetable family — including cabbage, cauliflower, brussels sprouts, watercress, and bok choy — go several steps further in disease prevention with their high concentrations of the powerful disease-fighting compounds isothiocyanates and indole-3-carbinol.
Getting five servings a day of fruits and vegetables makes a tremendous difference in disease prevention, but population-based research shows getting just three servings a week from the cruciferous vegetable family seems to provide powerful anticarcinogenic effects. Yet only 3% of Americans regularly eat cruciferous vegetables, say researchers at Arizona State University in Mesa.1
Here is the recent evidence in favor of broccoli and its cousins:
Prostate cancer protection: Researchers at the Fred Hutchinson Cancer Research Center in Seattle found that men who included three servings of cruciferous veggies, such as cabbage, in their weekly vegetable consumption lowered their prostate cancer risk by 41%.2 The study included 1,230 men ages 40 to 64 living in King County, Washington (Seattle area), 628 of them newly diagnosed with prostate cancer and 602 of them cancer-free. Self-administered food frequency questionnaires were used to assess diet over a three- to five-year period before diagnosis or recruitment to the study.
Results contradicted most other literature in the same field by showing significant protective effects of vegetables and even greater protective effects of cruciferous vegetables, but no protective effects associated with fruit intake. Participants who ate 28 servings or more of vegetables every week had a 35% improvement in the odds ratio compared to those who ate 14 servings or less a week.
Those who included just three servings of cruciferous vegetables a week in their vegetable intake were 41% less likely to develop prostate cancer. Incidentally, a less significant prostate cancer protective effect of 27% was associated with eating three or more servings of lycopene-rich cooked tomatoes a week, although other studies have suggested strong protective effects against other types of cancers.
"Our interpretation is that substitution of cruciferous vegetables for other vegetables, while keeping total vegetable intake constant, significantly reduces prostate cancer risk," the researchers wrote in the Journal of the National Cancer Institute.
Immune-enhancing effects
Alan Kristal, DrPh, associate director of the Fred Hutchinson cancer prevention research program, says the best causative guess lies in the elevation of glutathione S-transferase (GST) isoenzymes caused by indole-3-carbinols (indoles) and isothiocyanates (ISTs) present in cruciferous vegetables.
GSTs are phase II detoxification enzymes that inactivate carcinogenic electrophiles and organic hydroperoxides and protect cells from DNA-damaging agents. In lay terminology, ISTs and indoles found in cruciferous vegetables appear to prevent normal cells from mutating into cancerous cells by upregulating the immune system, he explains.
"Foods that protect against cancer appear to have an immune-enhancing effect, and it appears to be the indoles and ISTs, which have the strongest protective effect," says Kristal.
He notes the results of the study may be particularly important because the participants were men in an age group at low risk for prostate cancer. The incidence of prostate cancer in men under 65 is about 250 per 100,000 compared with 1,000 per 100,000 in men over 65.
A Guard against lung cancer: Research from the University of Minnesota Cancer Center in Minneapolis shows the compounds in cruciferous vegetables not only appear to provide protection against lung cancer; in lab studies and human studies, cruciferous vegetables also have been shown to neutralize the effects of cigarette smoking.3 ISTs to the rescue, again, says Stephen S. Hecht, PhD, professor of cancer prevention at the University of Minnesota Cancer Center.
Hecht notes that lung cancer is the leading cause of cancer death in the United States, claiming approximately 160,000 lives a year, 87% of them attributable to cigarette smoking. "While smoking cessation is the best way to prevent lung cancer, it has not been uniformly successful in the United States, where there are still 48 million smokers, many of whom may be addicted to nicotine," he says.
Eating broccoli won’t neutralize the effects of smoking, Hecht concedes, "[but] for the addicted smoker who cannot quit even after having tried smoking cessation programs using nicotine re-placement therapy, chemoprevention may be a feasible way to lengthen life and avoid lung cancer." ISTs are released upon maceration or chewing of cruciferous vegetables. "The remarkable ability of some ISTs to prevent cancer in laboratory animals treated with carcinogens stems from their favorable effects on carcinogen metabolism," says Hecht.
The power of ISTs
Since virtually all dietary or environmental carcinogens to which humans are exposed require enzymatic transformation to exert their carcinogenic effects, Hecht argues that ISTs also enhance carcinogen detoxification, and he speculates that ISTs have an effect on both processes.
The specific effect of ISTs on lung cancer comes from the constituent phenethyl isothiocyanate (PEITC), which Hecht’s research shows inhibits one of the major carcinogens in cigarette smoke, NNK-[4-methylnitrosamino-1-(3-pyridyl)-1-butanone]. In a small human study, Hecht measured PEITC and NNK levels in a group of smokers who abstained from consuming any cruciferous vegetables during the three-day study and then crossed over to consuming two ounces of watercress each day for three days.
The results showed the PEITC inhibits the oxidative metabolism of NNK in humans, suggesting its usefulness as a chemopreventive agent against lung cancer.
Hecht suggests that a logical extension of his research would be to find a construction of cancer-inhibitory compounds that could be used for preventing lung cancer in smokers who have failed in attempts to quit — and to decrease risk in ex-smokers. "Eating some cole slaw or adding it to a salad a few times a week is a pretty painless tool for your patients to minimize their risk of lung cancer, whether they smoke or not," he says.
Other early studies have shown chemoprotective and anti-metastasizing effects of cruciferous vegetables against other types of cancer, including breast, ovarian, colon, and esophageal, which are attributed to indoles, sulforaphane, and ISTs.
Heart strength: Members of the cabbage family are loaded with vitamins C and E and beta-carotene, which help reduce the risk of degenerative diseases by mopping up the free radicals that naturally accumulate in the body and damage healthy cells, causing changes that can lead to heart disease and other serious problems.
Some research has suggested that people with the highest intakes of beta-carotene have a dramatically lower risk of heart disease. A half-cup serving of cooked broccoli or a half-cup serving of raw cabbage each provides 0.7 mg of beta-carotene. The National Academy Press recommends five or more servings per day of fruits and vegetables, which would provide a total intake of 3 mg to 6 mg per day.4 Broccoli almost can be classified as a power food with 58 g of vitamin C, 2 g of fiber, 35 mg of calcium, 18 mg of magnesium, and 227 mg of potassium — all for only 22 calories in a half-cup cooked serving.
"All vegetables are good for your general health, but cruciferous vegetables are so nutritious that eating them at least three times a week, or even more, is probably one of the best choices anyone can make to promote good health," says Kristal.
References
1. Johnson C, Taylor C, Hampl J. More Americans are eating "5 A Day" but intakes of dark green and cruciferous vegetables remain low. J Nutr 2000; 130:3,063-3,067.
2. Cohen J, Kristal A, Stanford J. Fruit and vegetable intakes and prostate cancer risk. J Natl Cancer Inst 2000; 92:61-67.
3. Hecht S. Chemoprevention of cancer by isothiocyanates, modifiers of carcinogen metabolism. J Nutr 1999; 129:768-774.
4. National Academy Press. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC; 2000. Web site: books.nap.edu/books/0309069351/html/95.html. Accessed Feb. 7, 2001.
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content