What is vitamin E?
Vitamin E is a nutrient that may protect against chronic diseases such as cardiovascular disease. Vitamin E is being studied in the prevention of some types of cancer.
There are eight different forms of vitamin E: four tocopherols (alpha-, beta-, gamma-, and sigma-) and four tocotrienols (alpha-, beta-, gamma-, and sigma-). Compared with other tocopherols, alpha-tocopherol (the form of vitamin E commonly found in dietary supplements) is found in greater amounts in the body and is the most active. Most vitamin E in the diet comes from gamma-tocopherol. Food sources of vitamin E include vegetable oils, nuts, and egg yolks.
Many of the possible health benefits of Vitamin E may be from its antioxidant activity. Vitamin E is a powerful antioxidant that protects cell membranes from damage caused by free radicals. Vitamin E also has other functions involved in cell signaling pathways and gene expression.
How is vitamin E administered or consumed?
Vitamin E may be consumed in the diet or taken in dietary supplements.
Have any clinical trials (research studies with people) of vitamin E been conducted?
Population studies and clinical trials have been done to find out if vitamin E may be useful in preventing or treating prostate cancer.
Population studies look for risk factors and ways to control disease in large groups of people. Population studies of vitamin E in prostate cancer risk have shown the following:
- The NIH -AARP Diet and Healthy Study studied whether vitamin E in supplements and in the diet of volunteers may prevent prostate cancer. After 5 years, no link between vitamin E supplements and prostate cancer risk was found. However, a lower risk of advanced prostate cancer was found in those who had high intakes of one form of vitamin E (gamma-tocopherol).
- In a 2010 study that measured blood levels of trace elements and vitamin E, those who had prostate cancer had markedly lower blood levels of vitamin E than those who did not have prostate cancer. In addition, those who had higher PSA levels had lower levels of vitamin E in their blood.
- Blood levels of alpha-tocopherol and gamma-tocopherol and prostate cancer risk were studied in participants in the Prostate, Lung, Colorectal and Ovarian (PLCO) Screening Trial. Men with higher levels of alpha-tocopherol had lower rates of prostate cancer, but this was noted only in current smokers and those who had recently quit.
- In a review of many studies combined involving 370,000 men from several countries, higher blood levels of alpha-tocopherol were linked with a lower risk of prostate cancer in all patients, not just smokers.
Clinical trials of preventing or treating prostate cancer
- In the Physicians' Health Study II, men received either vitamin E supplements (400 IU synthetic alpha-tocopherol taken every other day) and/or vitamin C supplements (500 mg synthetic ascorbic acid taken daily) and were followed for an average of 8 years. The overall rates of prostate cancer were very similar in the men who received vitamin E supplements and in those who did not, suggesting that vitamin E may not prevent prostate cancer. Furthermore, vitamin E did not have an effect on total cancer or death rates in these participants.
- The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study (ATBC) trial measured blood levels of alpha-tocopherol and dietary intake of vitamin E in men who were followed for up to 19 years. Findings showed no link between vitamin E in the diet and prostate cancer risk, but showed that higher levels of alpha-tocopherol in the blood may be linked with a lower risk for developing advanced prostate cancer.
- Men in the ATBC trial who developed prostate cancer were studied to find out if serum alpha-tocopherol levels affected survival time. Higher serum alpha-tocopherol levels, at both time of diagnosis and at the 3-year time point, were linked with improved prostate cancer survival.
- A 2011 study of men who took part in The Carotene and Retinol Efficacy Trial (CARET) found that, among those who were current smokers, higher levels of serum alpha-tocopherols and gamma-tocopherols were linked with lower risk of aggressive prostate cancer.
The Selenium and Vitamin E Cancer Prevention Trial (SELECT)
The Selenium and Vitamin E Cancer Prevention Trial (SELECT) was a large clinical trial begun by the National Institutes of Health in 2001 to study the effects of selenium and/or vitamin E on the development of prostate cancer. Over 35,000 men, aged 50 years and older, were randomly assigned to receive one of the following combinations daily for 7-12 years:
- Vitamin E (alpha-tocopherol acetate, 400 IU/ day) and a placebo;
- Selenium (L-selenomethionine, 200 mcg/ day) and a placebo;
- Vitamin E and selenium; or
- Two placebos.
First SELECT results reported in 2009 found no meaningful differences in rates of prostate cancer among the 4 groups. In the Vitamin E alone group, there was a slight increase in the rate of prostate cancer and in the selenium alone group, there was a slight increase in the rate of diabetes. Based on those findings, the men in the study were advised to stop taking the study supplements.
Updated SELECT results in 2011 showed that selenium supplements had no meaningful effect on prostate cancer risk; however, men taking vitamin E alone had a 17% increase in prostate cancer risk compared to men in the placebo group.
In 2014, further SELECT results showed that vitamin E supplements alone had no effect on prostate cancer risk in men with high levels of selenium at the start of the trial; however, vitamin E supplements increased the risk of low-grade and high-grade prostate cancer in men with lower levels of selenium at the start of the trial.
Several factors may have affected study results, including the dose of vitamin E chosen and the form of selenium used.
Have any side effects or risks been reported from vitamin E?
Alpha-tocopherols are deemed Generally Recognized as Safe by the U.S. Food and Drug Administration.
In the Physicians' Health Study II, there were no marked differences in rates of gastrointestinal symptoms, fatigue, drowsiness, skin discoloration or rashes, or migraine between men who took vitamin E (400 IU every other day of alpha-tocopherol) and those who took a placebo. However, there was a higher number of hemorrhagic strokes in men who took vitamin E than in men who took a placebo. In the Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group, there was also an increase in hemorrhagic strokes among men in the group that took vitamin E (50 mg/ day of alpha-tocopherol).
Earlier results from the SELECT trial showed no marked differences in rates of less severe adverse effects (such as hair loss, inflamed skin, and nausea) in the groups that took vitamin E (400 IU/ day of all-rac-alpha-tocopherol) compared to the other treatment groups. Later follow-up of SELECT participants showed an increased risk of prostate cancer among men in the vitamin E alone group.
Is vitamin E approved by the U.S. Food and Drug Administration (FDA) for use as a cancer treatment in the United States?
The U.S. Food and Drug Administration has not approved the use of vitamin E as a treatment for cancer or any other medical condition.
Vitamin E is available in the United States in food products and dietary supplements. Because dietary supplements are regulated as foods, not as drugs, FDA approval is not required unless specific claims about disease prevention or treatment are made.