A diet rich in vitamin E appears to protect against both prostate cancer and bladder cancer, according to new research that lifts hopes for the vitamin after disappointing recent studies, writes Dominique Patton.
A case-control study found that diets high in alpha-tocopherol could more than halve the risk of bladder cancer compared to people with a low intake (abstract 3921). Other findings reported at the American Association for Cancer Research annual meeting this weekend suggest that vitamin E from both diet and supplements offers strong protection against prostate cancer.
Previous studies have found an association between higher intake of vitamin E and lower incidence of cancer of the prostate and breast. However, a recent investigation into the impact of diet on postmenopausal breast cancer in over 18,000 women failed to find evidence to support the vitamin's protective effect.
The vitamin has also been hailed as a safeguard against heart disease but the most recent trials have not confirmed the connection between the nutrient and reduced heart attacks or strokes.
The new findings will be welcomed by many in the supplements industry, seeing falling interest in vitamin E in recent years. Natural forms of the vitamin, said to be more potent than synthetic, are on the rise however with Cognis recently reporting a surge in the volume of its natural vitamin E sales of some 9 per cent last year.
Scientists from the University of Texas M.D. Anderson Cancer Center and Texas Woman's University are the first to report evidence for vitamin E's role against bladder cancer, the fourth leading cause of death in men in the US and high in other industrialized countries such as Canada, France, Denmark, Italy, and Spain.
"High intake of vitamin E from dietary sources alone was associated with a 42 per cent reduced risk of bladder cancer, whereas high intake of vitamin E from dietary sources and supplements combined reduced the risk by 44 per cent," said researcher Ladia M. Hernandez.
Hernandez and colleagues interviewed 468 bladder cancer patients and 534 healthy, cancer-free controls, for information on their diets and supplement use. A database with values assigned to the tocopherol content of foods, based on published values, was developed specifically for the study.
But while gamma-tocopherol is the most common tocopherol in the US diet, the researchers, the first to test the effects of this form of vitamin E on cancer risk, found it to have no protective effect against bladder cancer.
In the second study however (abstract 1096), researchers from the US National Cancer Institute, the Fred Hutchinson Cancer Research Center and the National Public Health Institute of Finland found that both alpha- and gamma-tocopherol lowered the risk of prostate cancer, by as much as 53 per cent and 39 per cent, respectively.
The scientists selected 100 men with prostate cancer and 200 without from the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study cohort of 29,133 Finnish men, aged between 50 and 69 years.
The ATBC study had previously demonstrated a 32 per cent reduction in the rate of prostate cancer among men who took 50 mg of alpha-tocopherol daily for a period of five to eight years.
The new study included those not taking supplements, to evaluate serum levels of alpha-tocopherol and gamma-tocopherol exclusively derived from dietary intake. But 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.
The studies appear to support an increase in dietary alpha-tocopherol, found in greater concentrations in the blood than the gamma form. This is in part because a protein in the liver called alpha-tocopherol transfer protein preferentially binds alpha-tocopherol and secretes it into the plasma.
The researchers noted that the higher consumption of rapeseed oil among Finns, compared to a preference for corn or soybean oils in the US, gave the Europeans higher intake of alpha-tocopherol.
Dietary vitamin E comes from nuts and seeds, wholegrain products, vegetable oils, salad dressings, margarine, beans and other vegetables. Spinach, green and red peppers and sunflower seeds were found to be excellent sources of alpha-tocopherol.