Read the label on your vitamin E supplements; they're not all the same. Vitamin E is actually eight different compounds, four tocopherols and four tocotrienols. Each type is designated alpha, beta, gamma, or delta, to indicate details of the chemical structure. Gamma tocopherol is the most common form in plant seeds and oils, and is reported to be the most effective for many health benefits, including cancer prevention. However, many supplements offer only the alpha tocopherol. How did this happen?
A decade ago, a review article in American Journal of Clinical Nutrition reported that gamma tocopherol is an under-appreciated nutrient. The alpha form is found in higher concentrations in human and animal tissue, and is essential for reproductive health. Standard lab tests for the biological activity of vitamin E are based on survival of embryos in pregnant rats. Thus alpha tocopherol alone is often marketed as vitamin E. However, the gamma form is more abundant in human tissue than in rodent tissue, and has additional chemical functions. Both are anti-oxidants. Gamma tocopherol and its metabolic product also have anti-inflammatory properties similar to aspirin and other NSAIDs.
Natural sources of gamma tocopherol include vegetable oils (corn, soybean, sesame, etc.) and nuts (walnuts, pecans, peanuts, etc.). The authors of Reference 1 reported that approximately 70 percent of the vitamin E in the typical U.S. diet is gamma tocopherol. Reference 2 reported that two studies found a significant correlation between high dietary intake of vitamin E and a lower risk of lung cancer. However, studies of vitamin E supplements have shown little effect on cancer risk. The authors suggested this discrepancy occurs because the supplements used in the studies are mostly synthetic alpha tocopherol. In studies of animal models, gamma tocopherol successfully prevented lung and colon cancers.
Alpha tocopherol is important for our health, but it's not the cancer fighter in vitamin E, according to both references. Gamma tocopherol is the one we want to reduce inflammatory damage that can lead to cancer.