As background information, the researchers wrote:
"Lifetime risk of prostate cancer in the United States is currently estimated to be 16 percent. Although most cases are found at an early, curable stage, treatment is costly and urinary, sexual, and bowel-related adverse effects are common."
Epidemiological and preclinical evidence had so far pointed towards prostate cancer preventive benefits associated with vitamin E and selenium supplements.
The authors added:
"The initial report (December 2008) of the Selenium and Vitamin E Cancer Prevention Trial (SELECT) found no reduction in risk of prostate cancer with either selenium or vitamin E supplements but a statistically nonsignificant increase in prostate cancer risk with vitamin E. Longer follow-up and more prostate cancer events provide further insight into the relationship of vitamin E and prostate cancer."
Eric A. Klein, M.D. and team set out to determine what the long-term effects of vitamin E and selenium might be on prostate cancer risk among men of relatively good health. They gathered data on 35,533 males from 427 study centers in Puerto Rico, Canada and the USA, who were randomized between August 2001 and June 2004.
They only selected males with a PSA measure below a certain level, a digital rectal examination that did not point towards a suspicion of prostate cancer, aged 50 years or more for African-Americans and 55 for other males.
In the primary analysis, 34,887 men were randomly selected into one of the four following groups:
- Selenium group - 8,752 men received 200 micrograms of selenium per day
- Vitamin E group - 8,737 men received 400 IU per day
- Double group - 8,702 men received both selenium and vitamin E
- Placebo group - 8,696 men received supplement-looking dummy tablets
A total of 521 additional prostate cancers have been reported since the initial report - in the following groups:
- Placebo group - 113 cases
- Vitamin E group - 147 cases
- Selenium group - 143 cases
- Combination group - 118 cases
When looking at the total prostate cancer rate, not just the increase since the initial report, the numbers were as follows:
- Placebo group - 529
- Vitamin E group - 620
- Selenium group - 575
- Combined group - 555
The authors wrote:
"In this article, we report an observation of important public health concern that has emerged with continued follow-up of SELECT participants. Given that more than 50 percent of individuals 60 years or older are taking supplements containing vitamin E and that 23 percent of them are taking at least 400 IU/d despite a recommended daily dietary allowance of only 22.4 IU for adult men, the implications of our observations are substantial."
The greater prostate cancer risk among those in the vitamin E group was only detectable after extended follow-up. This means that the effects of vitamin E can linger, even after the individual stops taking the supplement. For any study to be meaningful and relevant, the authors say the follow-up period needs to be long.
The researchers also added that when assessing the benefits and drawbacks of micronutrients as dietary supplements, studies need to be large-scale, population-based, and randomized.
"The observed 17 percent increase in prostate cancer incidence demonstrates the potential for seemingly innocuous yet biologically active substances such as vitamins to cause harm. The lack of benefit from dietary supplementation with vitamin E or other agents with respect to preventing common health conditions and cancers or improving overall survival, and their potential harm, underscore the need for consumers to be skeptical of health claims for unregulated over-the-counter products in the absence of strong evidence of benefit demonstrated in clinical trials."
Vitamin EVitamin E belongs to a group of fat-soluble compounds, including tocopherols and tocotrienols. Y- tocopherol is the most common type of vitamin E in the American diet, and can be found in margarine, soybean oil, corn oil and dressings. α-Tocopherol is the second most common form of vitamin E in the North American diet, it is also the biologically most active, and can be found in sunflower oil, safflower oil, and wheat germ oil.
Vitamin E is a fat-soluble antioxidant that halts the production of reactive oxygen species that are formed when fat is oxidized.
α-tocopherol form of vitamin E
Reports have indicated that vitamin E may have benefits for:
- A vitamin E pre-cursor may protect against a kind of breast cancer
- Better diabetes control
- Certain skin conditions
- Improving the immune system in elderly people
- Lowering chronic obstructive pulmonary disease (COPD) in about 10% of both non-smokers and smokers
- Male fertility
- Parkinson's disease
- PMS (premenstrual syndrome)
- Protecting from Alzheimer's disease
- The prevention of heart disease