US researchers suggest, based on animal experiments, that dietary vitamin E in the form of gamma- and delta-tocopherol could be beneficial in reducing the risk of, and even treating, certain cancers. Experts criticized that animal models do not accurately reflect human metabolism and that cancer development depends on multiple factors.
The scientists reported that rodents exposed to cancer-causing substances and whose feed included two forms of vitamin E – gamma- and delta-tocopherol – had fewer and smaller tumors (1). When cancer cells were injected into mice, these tocopherols also slowed down the development of tumors.
The researchers speculated that gamma- and delta-tocopherol, which can be found in nuts and soybean, canola and corn oils, could help reduce the risk of different forms of cancer, such as cancer of the colon, lung, breast and prostate. They noted that supplements may not have these beneficial effects because they generally contain alpha-tocopherol, which failed to show a cancer risk reduction in several large-scale human trials. For people who need to take a vitamin E supplement, they recommended that taking a mixture of vitamin E resembling what is in our diet would be the most prudent supplement to take.
Experts commented that, among the tocopherol isomers, alpha-tocopherol is the most prevalent form of vitamin E that is intentionally retained in the human body. It is retained three times longer than, for example, gamma-tocopherol (2). Alpha-tocopherol is the only form that has a recommended dietary allowance ( RDA), which was set at 15 mg per day. A diet rich in fruits and vegetables and low in fat probably contains less than 15 mg of alpha-tocopherol. Moreover, dietary alpha-tocopherol intake has decreased over the past 50 years, not as a result of losses in food processing, but of changes in recipes of processed foods.
Alpha-tocopherol appears to have potent effects on cellular functions. It can, for example, modulate the inflammatory responses in white blood cells and regulate vascular tone, while maintaining artery wall flexibility. According to the experts, the identification of alpha-tocopherol function in humans would be key in establishing human vitamin E requirements. Only alpha-tocopherol has a protein that regulates its plasma concentrations. This observation argues for a unique and important physiological role for this vitamin E form.