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 *-tocopherol and *-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 *-tocopherol and *-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 *-tocopherol per day for a period of five to eight years.
Since the baseline value for serum levels of *-tocopherol and *-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 *-tocopherol and *-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 *-tocopherol and *-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 *- and *-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 (*-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 *-tocopherol) from dietary sources only, from diet and supplements combined, and from dietary *-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 *-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, *-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 *-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.
Catalase (CAT) genotype, dietary antioxidants, and breast cancer risk: Abstract No. 2313
In the first study ever to evaluate catalase (CAT) genotypes and breast cancer, researchers at Roswell Park Cancer Institute in Buffalo, N.Y., found that women with the most common genotype for reducing oxidative stress are at a reduced risk of developing breast cancer. Further, they can diminish their breast cancer risk even more by including ample fruits and vegetables in their diets.
Fruits and vegetables are well known to reduce the risk of some cancers through their antioxidant properties; that is, by inhibiting reactive oxidant species. These free radicals form naturally in the course of cell respiration and metabolism, but have been linked with disease-causing damage to tissue and changes in DNA that can lead to malignancies.
While this oxidative stress is considered to be a major causative factor for breast cancer, prominent research including the Nurses Health Study has shown no link between increased consumption of fruits and vegetables and decreased breast cancer risk. Because the evidence on whether fruits and vegetables reduce the risk of breast cancer is not clear, the investigators from Roswell Park thought that effects might be limited to women with specific genotypes related to protection from oxidative stress.
Jiyoung Ahn, M.S., R.D., a pre-doctoral research associate in the department of epidemiology at Roswell Park, and a Ph.D. student in the division of nutritional sciences at Cornell University, considered the fact that catalase (CAT) is one of the most effective enzymes in the body for reducing oxidative stress. It converts hydrogen peroxide into water and oxygen, thus neutralizing reactive oxygen species. Ahn wondered if higher levels of the endogenous antioxidants that course through the human blood stream naturally - like those resulting from the CAT C (CC) allele - might provide some degree of antioxidant protection against breast cancer, and if the risk might be further diminished by the consumption of fruits, vegetables and specific antioxidants.
Working with her academic advisor, Christine Ambrosone, Ph.D., chair of the Roswell Park department of epidemiology, Ahn evaluated this hypothesis in a population-based, case-control study of 1,037 women with breast cancer and 1,086 healthy subjects in Nassau and Suffolk Counties, N.Y., conducted originally by Marilie Gammon, Ph.D., and colleagues. Each woman was interviewed at home to assess suspected breast cancer risk factors over the course of her lifetime, and administered the Block food frequency questionnaire to determine dietary intake the preceding 12 months.
The women were genotyped, with the most common genotype the CAT C (CC), present in a little more than 60 percent of the cases and the controls. A CT polymorphism exists in the (CAT) gene in about 33 percent of participants, and all others - some four percent - have the TT genotype.
Women with the CC genotype and a diet rich in fruits and vegetables had a 30 percent reduced risk of breast cancer. There was only a five percent lower risk in women with the CC genotype who ate very few fruits and vegetables.
"With so many women having the CC genotype," said Ahn, "our study potentially has a very important public health impact. Of course, none of us knows our exact genetic make-up, but since eating a diet high in fruits and vegetables is known to contribute to a healthy lifestyle anyway, women can consider it a viable means of reducing their breast cancer risk, as well."
Founded in 1907, the American Association for Cancer Research is a professional society of more than 22,000 laboratory, translational, and clinical scientists engaged in all areas of cancer research in the United States and in more than 60 other countries. AACR's mission is to accelerate the prevention and cure of cancer through research, education, communication, and advocacy. Its principal activities include the publication of five major peer-reviewed scientific journals: Cancer Research; Clinical Cancer Research; Molecular Cancer Therapeutics; Molecular Cancer Research; and Cancer Epidemiology, Biomarkers & Prevention. AACR's Annual Meetings attract more than 15,000 participants who share new and significant discoveries in the cancer field. Specialty meetings, held throughout the year, focus on the latest developments in all areas of cancer research.