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OHSU Cancer Institute, VA Researcher Finds Vegetables May Help Protect Against Prostate Cancer

   Portland, Ore.

Our parents may have been on to something when they told us to eat our vegetables, finish eating every pea and bean on our plates.

In two separate studies it was found that nutrients in certain foods might reduce the risk for prostate cancer, according to Jackilen Shannon, Ph.D., M.P.H., a member of the Oregon Health & Science University Cancer Institute and the Portland Veterans Affairs Medical Center. Shannon will present these findings Tuesday, Nov. 14 between 6 and 8 p.m. in Boston, Mass., at the Fifth Annual International Conference of the American Association of Cancer Research Frontiers in Cancer Prevention.

In the "Folate Nutrition, Alcohol Consumption and Prostate Cancer Risk" study, Shannon looked at the folate and alcohol consumption among two groups of veterans: 137 men who had been diagnosed with prostate cancer and 238 men who had a normal prostate specific antigen (PSA) level and thus were considered to be at low risk for prostate disease. Folate is found in foods such as dark, green leafy vegetables; liver; kidney; dried beans and mushrooms. Folate is required for the production of red blood cells but also plays an important role in inhibiting a certain type of DNA damage known as methylation. DNA damage is thought to be important in the development of cancer.

"Folate seems to be protective against prostate cancer. As compared with men with low levels of folate intake (336 micrograms a day or less), men consuming the highest amount of folate (530 micrograms a day or greater) were 52 percent less likely to have prostate cancer," Shannon said. It also appears that folate was most effective when the men ate foods containing the nutrient rather than a vitamin supplement. The current recommended dietary intake for folate in men older than 19 is 400 micrograms a day.

Shannon found no association between alcohol use and prostate cancer risk. But, she did find that among men who consumed greater amounts of alcohol - more than three drinks a day - the effect of folate was no longer significant. Folate appears to be effective primarily among men who were light to medium drinkers - one to two drinks a day.  It is not clear whether this is because alcohol interferes in the proper metabolism of folate or whether heavy alcohol consumers simply consume less folate.

In the second study, Shannon studied the effect of dietary intake of certain antioxidant nutrients, including beta-carotene, lycopene, vitamin C and vitamin E, to see if they help protect against prostate cancer among current, previous and nonsmokers. She used the same group of men as in the previous analyses.

Carotenoids and vitamin C are nutrients found in carrots, spinach, peaches, apricots, sweet potatoes, pumpkin, red and yellow peppers, oranges, tangerines, peaches, nectarines and papayas, while vitamin E is found primarily in oils from nuts and seeds as well as fortified cereals. Antioxidant nutrients play an important role in maintaining healthy cells and protecting them from DNA damage due to oxidative stress.  Antioxidants have been proposed as a potential key compound that may explain the cancer protective effect of fruits and vegetables. Cigarette smoking does just the opposite, causing oxidative stress to cells.

"After taking into account a man's age, race, body size and family history of prostate cancer, we saw that dietary intake of lycopene was associated with a lower risk of prostate cancer, and that when we looked at men who smoked, we saw this protective effect to be strongest in current and former smokers," Shannon said.

One in six men in the United States can expect to be diagnosed with cancer. Prostate has remained the most common non-skin cancer among men in this country.

The OHSU Cancer Institute is the only cancer center designated by the National Cancer Institute between Sacramento and Seattle. It comprises some 120 clinical researchers, basic scientists and population scientists who work together to translate scientific discoveries into longer and better lives for Oregon's cancer patients. In the lab, basic scientists examine cancer cells and normal cells to uncover molecular abnormalities that cause the disease. This basic science informs more than 200 clinical trials conducted at the OHSU Cancer Institute.
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Shannon is a scientist in the Center for Occupational and Environmental Toxicology, research scientist at the Portland Veterans Affairs Medical Center; assistant professor of public health and preventive medicine, OHSU School of Medicine; and member of the OHSU Cancer Institute's Cancer Prevention, Control, and Population-Based Studies Program and the Prostate Cancer focus group of the Solid Tumors Program, with an emphasis on epidemiology and cancer prevention
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