SEATTLE - Move over, tomatoes! All vegetables - especially broccoli, cabbage and their cruciferous cousins - may substantially reduce the risk of prostate cancer, according researchers at the Fred Hutchinson Cancer Research Center. Eating just three servings of vegetables a day can cut a man's risk of prostate cancer nearly in half. While carrots, beans, greens and cooked tomatoes all were found to decrease risk, the strongest effect was for cruciferous vegetables. These findings will appear in the Jan. 5 issue of the Journal of the National Cancer Institute.
"The bottom line is that if you eat a lot of vegetables, you can cut your risk of prostate cancer by about 45 percent," says Alan Kristal, Dr.P.H., co-investigator of the study. "And, if some of those vegetables are from the cruciferous family, like broccoli and cabbage, you may reduce your risk even further."
Kristal and Jennifer Cohen, Ph.D., from the Center's Cancer Prevention Research Program, led the data analysis. Janet Stanford, Ph.D., head of the Center's Prostate Cancer Research Program, also participated. All are from the Center's Public Health Sciences Division.
The study looked at the associations of total fruit and vegetable consumption, as well as specific types of fruits and vegetables, on prostate-cancer risk in 1,230 Seattle-area men. Half of the men had been diagnosed with prostate cancer and the other half were randomly selected men living in the Puget Sound region. Funded by the National Cancer Institute, this study was unique because it examined risks for prostate cancer in younger men (ages 40-64). By focusing on men who are at a very low risk of prostate cancer, the researchers were better able to assess the impact of lifestyle factors, such as diet, on cancer risk. The men were interviewed about their dietary habits three to five years prior to diagnosis (or an equivalent time frame among the control group). They also completed a detailed dietary questionnaire that asked how much and how often they ate 99 foods.
Men who ate three or more servings of vegetables a day (about 15 percent of the sample) had a 48 percent lower risk of prostate cancer, compared to men who ate fewer than one serving a day (also about 15 percent of the sample). This association was independent of other dietary factors, such as fat intake, and for medical factors, such as history of prostate cancer in a father or brother.
The strongest effect was for cruciferous vegetables, which include broccoli, cauliflower, brussels sprouts, and cabbage-based dishes such as sauerkraut and coleslaw. Men who ate three or more half-cup servings of cruciferous vegetables per week had a 41 percent decreased risk for prostate cancer, compared to men who ate fewer than one serving per week.
"At any given level of total vegetable consumption, as the percent of cruciferous vegetables increased, the prostate-cancer risk decreased," Kristal says.
Fruit, on the other hand, was a different story. When measuring the impact of total fruit intake as well as that of specific fruits, such as citrus, the researchers found no associations with reduced risk of prostate cancer. The researchers also found no special benefits for cooked tomatoes. This finding contradicts much-publicized research extolling the prostate-cancer-fighting properties of cooked tomato products, an effect attributed to a carotenoid called lycopene, a pigment that gives the fruit its red color.
"We found no association between lycopene and decreased prostate-cancer risk," Kristal says. "We also looked at foods that were good sources of lycopene, such as spaghetti sauce and pizza. These were not related to cancer risk at all." These results support four earlier studies that found no association between either tomato consumption or lycopene intake and risk of prostate cancer. The handful of studies to date that have shown protective effects have not controlled for total vegetable consumption, a flaw in study design, Kristal believes, that makes it difficult to accurately assess the cancer-fighting role of specific types of vegetables.
Scientists believe that vegetables protect against cancer because they contain a wide variety of phytochemicals. Many phytochemicals increase the activity of enzymes that can detoxify cancer-promoting compounds in the body. So if vegetables are good, would specific dietary supplements containing megadoses of these phytochemicals be better? "I think it would be a complete mistake; a significant error," Kristal says. "Vegetables - all food, actually - contain many biologically active components. We have some clues about which ones may be active in preventing prostate cancer, but it's not likely to be lycopene or any one single compound. It's much more likely to be the result of many compounds working together in very complex ways.
"It is therefore much more important to eat a variety of different vegetables. I don't think pills will take the place of eating a good diet, at least not in my lifetime."
On a related note: Watch for an upcoming editorial by Drs. Alan Kristal and Jennifer Cohen entitled "Tomatoes, Lycopene and Prostate Cancer: How Strong is the Evidence?" in the Jan. 15 issue of the American Journal of Epidemiology (media embargo lifts Jan. 10).
For more information, please contact Kristen Woodward, Hutchinson Center Media Relations, 206-667-5095.
SIDEBAR: Menu tips for a prostate-cancer prevention diet
Whether eating to prevent prostate cancer or to promote general good health, it's easy to incorporate at least three servings of vegetables per day into one's diet. Dr. Alan Kristal of the Fred Hutchinson Cancer Research Center, a cancer-prevention researcher who is also a trained chef, suggests the following sample menu:
The Fred Hutchinson Cancer Research Center is an independent, nonprofit research institution dedicated to the development and advancement of biomedical technology to eliminate cancer and other potentially fatal diseases. Recognized internationally for its pioneering work in bone-marrow transplantation, the Center's four scientific divisions collaborate to form a unique environment for conducting basic and applied science. The Hutchinson Center is the only National Cancer Institute-designated comprehensive cancer center in the Pacific Northwest.
For more information, visit the Center's Web site at http://www.fhcrc.org.
EMBARGOED FOR RELEASE: 4 JANUARY 2000 AT 16:00 ET US
Contact: Kristen Woodward
Fred Hutchinson Cancer Research Center