Have any studies of vitamin E been done in people?
Population studies and clinical trials have been done to find out if vitamin E may prevent or treat prostate cancer. Results have been mixed.
- The National Institutes of Health-American Association of Retired Persons (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 took high amounts of gamma-tocopherol.
- In a 2010 study that measured blood levels of trace elements and vitamin E, those who had prostate cancer had 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.
- In a review of combined studies with 370,000 men from several countries, higher blood levels of alpha-tocopherol were linked with a lower risk of prostate cancer in all patients.
Clinical trials to prevent or treat prostate cancer
- In the Physicians' Health Study II, men received either vitamin E supplements and/or vitamin C supplements and were followed for about 8 years. The overall rates of prostate cancer were similar in the men who received vitamin E supplements and in those who did not, suggesting that vitamin E may not prevent prostate cancer. Vitamin E did not affect total cancer or death rates.
- 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. Results 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 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 and a placebo.
- Selenium and a placebo.
- Vitamin E and selenium.
- Two placebos.
First SELECT results reported in 2009 found no differences in rates of prostate cancer among the 4 groups. In the Vitamin E alone group, there was an increase in the rate of prostate cancer and in the selenium alone group, there was an 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 effect on prostate cancer risk, but 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, but 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 and the form of selenium used.
A cohort study of 1,434 men in SELECT suggested that variations in certain genes which control the ways selenium and vitamin E are used by the body may have an effect on the risk of prostate cancer, including high-grade prostate cancer.