Questioning the Report that Vitamin E Causes Prostate Cancer
The Journal of the American Medical Association recently published a study suggesting that vitamin E may increase a man’s risk of developing prostate cancer. While the study findings are cause for concern, they support existing evidence that taking the isolated alpha-tocopheral form of vitamin E apart from the other tocopherols found in vitamin E’s natural form may be the problem. Natural vitamin E, in which its four forms are mixed together, has not been shown to increase prostate cancer risk, and might even offer some protection.
In the study, 35,533 men were randomly assigned to receive 400 IU per day of vitamin E (in the form of alpha-tocopherol) or a placebo for an average of five and a half years, and the men were then followed for a total of approximately seven years. During that time, 17% more men developed prostate cancer in the vitamin E group than in the placebo group, a statistically significant difference.
“E’s” not all equal
Although the study was well designed, it only examined one type of vitamin E, which is not how it occurs naturally. Vitamin E is found in food in four different forms: alpha-, beta-, gamma-, and delta-tocopherol. However, alpha-tocopherol is the form most commonly sold and studied, as early research suggested that most, if not all, of the biological activity of vitamin E is due to alpha-tocopherol. But it is now known that at least one of the other components—gamma-tocopherol—has important functions. Furthermore, large doses of alpha-tocopherol have been shown to deplete gamma-tocopherol, potentially upsetting the natural balance of the different forms of vitamin E in the body. “Mixed tocopherols,” on the other hand, a supplement that contains all four types of vitamin E, would not be expected to cause such an imbalance.
In a previous study, both alpha-tocopherol and gamma-tocopherol inhibited the growth of human prostate cancer cells in a test tube, but gamma-tocopherol was the more potent of the two. In another study, higher blood levels of alpha-tocopherol and gamma-tocopherol were each associated a lower risk of developing prostate cancer, but gamma-tocopherol’s protective effects were greater than that alpha-tocopherol’s.
These observations raise the possibility that alpha-tocopherol actually may protect against prostate cancer (contrary to the results of the new study) when given in amounts that do not negatively affect the body’s chemistry. When alpha-tocopherol is given by itself in large doses (such as 400 IU per day or more), it depletes gamma-tocopherol, which could more than negate any beneficial effect that alpha-tocopherol might have. Thus, taking vitamin E as mixed tocopherols would not be expected to increase prostate cancer risk, and might even help prevent prostate cancer. Further research is needed to examine that possibility.
By Alan Gaby, MD