Researchers: Diet a Significant Factor in Reducing Risk of Three Common Cancers

Scientists report vitamin E may protect against bladder, prostate cancers; fruits and vegetables rich in antioxidants lower breast cancer risk among women with specific genetic profiles

ORLANDO – While those wanting to lose weight consider the relative merits of counting carbs versus counting calories, those hoping to lower their risk for three of the most prevalent forms of cancer may be better off doing as Mother said: Take your vitamins and eat your vegetables.

Two case-control studies presented here today at the 95th Annual Meeting of the American Association for Cancer Research compared specific eating habits of healthy individuals to those with prostate and bladder cancers to assess the relationship between dietary factors and incidence of disease. Both found inverse associations between diet and cancer risk.

A third case-control study of breast cancer found that the effects of genetics were modified greatly by dietary antioxidants.

Higher serum á-tocopherol and ã-tocopherol concentrations are associated with lower prostate cancer risk: Abstract No. 1096

Two forms of vitamin E – alpha- and gamma-tocopherol – appear to lower the risk of prostate cancer by as much as 53 percent and 39 percent, respectively, based on the findings of a team of scientists from the National Cancer Institute, the Fred Hutchinson Cancer Research Center in Seattle and the National Public Health Institute of Finland.

The researchers, led by Stephanie J. Weinstein, M.S., Ph.D., and Demetrius Albanes, M.D., of the NCI Nutritional Epidemiology Branch, Division of Cancer Epidemiology and Genetics, drew their subjects from the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study cohort of 29,133 Finnish men, aged between 50 and 69 years. From that group were selected 100 men with prostate cancer and 200 without, to determine whether there exists an association between higher levels of á-tocopherol and ã-tocopherol circulating in the blood stream and lower risks of prostate cancer. The ATBC Study previously had demonstrated a 32 percent reduction in the rate of prostate cancer among men who took 50 mg of á-tocopherol per day for a period of five to eight years.

Since the baseline value for serum levels of á-tocopherol and ã-tocopherol in this study came from blood drawn before men in the ATBC trial started taking any pills, use of vitamin E supplements was a factor only if the participants had been taking them already. Ten percent had, leaving 90 percent whose serum levels of á-tocopherol and ã-tocopherol could be attributed exclusively to dietary intake. In addition, in keeping with earlier findings, the men who were randomized to receive a vitamin E supplement as part of the ATBC trial and who had the highest serum vitamin E levels at baseline displayed the lowest risk of prostate cancer.

“Nuts and seeds, whole grain products, vegetable oils, salad dressings, margarine, beans, peas and other vegetables are good dietary sources of vitamin E,” Weinstein said.

She explained the striking difference in the relative amounts of á-tocopherol and ã-tocopherol in the body compared to dietary contents.

“Even though gamma-tocopherol is by far more prevalent in U.S. diets,” noted Weinstein, “alpha-tocopherol is found in greater concentrations in the blood. That is at least in part because a protein in the liver called alpha-tocopherol transfer protein preferentially binds alpha-tocopherol and secretes it into the plasma.”

Weinstein further noted that one principal dietary difference between Finns and Americans is the type of cooking oils used. “The Finns generally eat more canola oil,” she said, “while Americans favor corn or soybean oils. Canola oil is richer in alpha-tocopherol and offers the added benefit of being lower in saturated fat.”

To achieve optimum serum levels of á- and ã-tocopherols, Weinstein recommends following the Dietary Guidelines for Americans, published by the U.S. Department of Agriculture and the U.S. Department of Health and Human Services. They call for eating more fruits, vegetables and whole grains, and fewer fats and sugars.

Intake of vitamin E (2-R isomers of alpha-tocopherol) and gamma-tocopherol in a case-control study and bladder cancer risk: Abstract No. 3921

Consuming vitamin E (á-tocopherol) lowers the risk of bladder cancer, according to the findings of a case-control study led by Xifeng Wu, M.D., Ph.D., M.S., from the University of Texas M.D. Anderson Cancer Center in collaboration with researchers at Texas Woman’s University, both in Houston.

M.D. Anderson research dietician Ladia M. Hernandez, M.S., R.D., L.D., also a doctoral student at Texas Woman’s University; Professor John D. Radcliffe, Ph.D., M.Sc., R.D., of Texas Woman’s University; and several epidemiologists at M.D. Anderson evaluated the association between intake of vitamin E (2-R isomers of á-tocopherol) from dietary sources only, from diet and supplements combined, and from dietary ã-tocopherol. Personal interviews were conducted with 468 bladder cancer cases and 534 healthy, cancer-free controls, using a modified version of the National Cancer Institute’s Health Habits History Questionnaire. The questionnaire was modified to incorporate supplements use and ethnic dishes commonly consumed in the Houston area. Radcliffe developed a database with values assigned to the tocopherol content of foods, based on published values and values for such foods as cornbread, French fries and tomatillos, determined specifically for the study. He found almonds, spinach, mustard greens, green and red peppers and sunflower seeds to be excellent sources of á-tocopherol.

“High intake of vitamin E from dietary sources alone was associated with a 42 percent reduced risk of bladder cancer, whereas high intake of vitamin E from dietary sources and supplements combined reduced the risk by 44 percent,” Hernandez reported.

As NCI’s Weinstein also pointed out, ã-tocopherol is the most common tocopherol in the U.S. diet. Even so, its effect on cancer risk had never before been tested in a case-control study. Hernandez and her colleagues found ã-tocopherol to have no protective effect against bladder cancer.

Wu noted that the rate of bladder cancer is four times higher among men generally, and one-and-a-half times higher in whites. Bladder cancer is the fourth leading cause of cancer death in men. More than 55,000 incidents were reported last year; during the same time, 12,500 bladder cancer-related deaths occurred.

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