One form of vitamin E appears beneficial in reducing bladder cancer risk
ORLANDO -- One form of vitamin E appears to offer protection against development of bladder cancer, while a second form has no beneficial effect, say a team of researchers led by The University of Texas M. D. Anderson Cancer Center. These findings were presented at the annual meeting of the American Association for Cancer Research.
In a five-year study, which included 468 newly diagnosed bladder cancer patients and 534 cancer-free controls, the researchers found that high dietary intake of alpha-tocopherol, one form of vitamin E, significantly reduced the risk of developing bladder cancer.
But gamma-tocopherol, which is consumed in greater amounts than alpha-tocopherol in the United States, offered no protection, say the researchers, led by Xifeng Wu, M.D., Ph.D., associate professor in the Department of Epidemiology at M. D. Anderson, and including nutritionists from Texas Woman's University as well as epidemiologists from M. D. Anderson.
"High intake of vitamin E from dietary sources was associated with a 42 percent reduced risk of bladder cancer whereas a high intake of vitamin E from diet and supplements combined reduced the risk by 44 percent," says the study's first author, research dietician Ladia Hernandez, M.S., R.D. L.D., research dietitian in the Department of Epidemiology at M. D. Anderson.
"The study is not over, but my advice is that everyone should eat a healthy diet that includes fruit, vegetables and nuts," says co-investigator, John Radcliffe, Ph.D., R.D., of the Department of Nutrition and Food Sciences at Texas Woman's University. "Most people now do not meet the recommended dietary allowance of 15 milligrams of vitamin E from their diet; typical dietary intake is 8 milligrams per day."
Many vegetables, nuts, fruits and oils contain both forms of vitamin E, but those richest in alpha-tocopherol include almonds, red and green peppers, spinach, mustard greens, sunflower seeds and vegetable oils, including cottonseed and safflower oils, say the researchers based on their extensive food analysis. Those high in gamma-tocopherol include walnuts, pecans, garbanzo beans and soybean oil.
Previous research tentatively linked low intake of vitamin E to bladder cancer, but those studies did not distinguish between the different forms of vitamin E, which include four tocopherols. Only the alpha and gamma forms of tocopherol are predominate in food, and because they are metabolized differently, a recent Institute of Medicine report suggested they should be studied separately.
To do that meant that Radcliffe and Hernandez developed a database for the alpha- and gamma-tocopherol contents of 200 different foods, based on an extensive review of published values and their own analytical values for foods like cornbread and french fries. These values were used to estimate the intakes of the two tocopherols in an ongoing case-control study.
Participants answered a detailed food-frequency questionnaire that summed up their dietary habits the year before they were diagnosed with the bladder cancer or, in the cancer-free control group, the year before they agreed to participate in the study. The researchers then factored out other known risks for developing bladder cancer, such as smoking, age, ethnicity and gender, to determine the benefits of the two forms of vitamin E.
"Our long term goal is to identify risk factors that are important for bladder cancer development," says Wu.
Radcliffe says more studies are suggesting that different vitamins protect against different forms of cancer, and some point to a benefit from gamma-tocopherol in reducing the risk of developing prostate cancer. "There are theories as to how these vitamins work to protect against disease, but we need more research to elucidate the details of the mechanisms involved."