The study – published in Cancer Prevention Research – assessed the cancer benefits of various vitamin E forms that have been suggested to have beneficial effects in epidemiologic studies.
However the authors, led by Chung Yang from Rutgers University and and the Cancer Institute of New Jersey, USA, noted that several recent large-scale human trials with alpha-tocopherol – the most commonly recognised and used form of vitamin E – have failed to show a cancer risk reduction.
"There are studies suggesting that vitamin E actually increases the risk of cancer and decreases bone density," said Yang. "Our message is that the vitamin E form of gamma-tocopherols …and delta-tocopherols … are beneficial in preventing cancers while the form of vitamin E, alpha- tocopherol, the most commonly used in vitamin E supplements, has no such benefit."
The vitamin E family
Overall, there are eight forms of vitamin E: four tocopherols (alpha, beta, gamma, delta) and four tocotrienols (alpha, beta, gamma, delta). Alpha-tocopherol (alpha-Toc) is the main source found in supplements and in the European diet, while gamma-tocopherol (gamma-Toc) is the most common form in the American diet.
Tocotrienols are only minor components in plants, although several sources with relatively high levels include palm oil, annatto, cereal grains and rice bran.
The authors said the two forms of vitamin E – gamma and delta-tocopherols – which can be found in soybean, canola, corn oils and nuts, could help to reduce the risk of cancers such as colon, lung, breast and prostate cancer. They noted that animal models have shown the two forms of vitamin E can block cancer formation and reduce growth in.
"When animals are exposed to cancer-causing substances, the group that was fed these tocopherols in their diet had fewer and smaller tumors," explained Yang. "When cancer cells were injected into mice these tocopherols also slowed down the development of tumors."
The lead researcher added that supplements may not have these beneficial effects because they generally contain alpha- tocopherol – which the data suggests has no benefit for cancers.
“On the basis of these results as well as information from the literature, we suggest that vitamin E, as ingested in the diet or in supplements that are rich in gamma- and delya-tocopherols, is cancer preventive; whereas supplementation with high doses of alpha-tocopherol is not,” warned the researchers.
Need for supplements?
Yang added that for people who need to take a vitamin E supplement, "taking a mixture of vitamin E that resembles what is in our diet would be the most prudent supplement to take."
The research director added that it is important to further to distinguish between the different forms of vitamin E, and conduct more research on the cancer preventive and other biological effects of each individual form.
Source: Cancer Prevention Research
Published online ahead of print, doi: 10.1158/1940-6207.CAPR-12-0045
“Does Vitamin E Prevent or Promote Cancer?”
Authors: C.S. Yang, N. Suh, A-N.T. Kong