Vitamin E, a vitamin supplement that was once believed to reduce the risk of developing cancer, might end up increasing the risk of developing prostate cancer in men who have taken the supplement for 5 years or longer.
The study also found that the risk of developing prostate cancer remained higher in men even if they had stopped taking the vitamin supplement.
The findings were part of the Selenium and Vitamin E Cancer Prevention Trial (SELECT), which studied 35,533 men from 427 study sites in the United States, Canada, and Puerto Rico between August 22, 2001, and June 24, 2004.
"For the typical man, there appears to be no benefit in taking vitamin E, and in fact, there may be some harm," said Eric Klein, MD, chair of the Glickman Urological and Kidney Institute at the Cleveland Clinic and lead author of the study.
In the study, men were randomly assigned into 1 of 4 groups: 8752 patients received selenium; 8737 received vitamin E; 8702 received both selenium and vitamin E; and 8696 received a placebo. Patients had to have a prostate-specific antigen (PSA) of 4.0 ng/mL or less, a digital rectal examination not suspicious for prostate cancer, and they had to be aged ³55 years old (or ³50 years for black men, a demographic of patients that are at an increased risk for developing prostate cancer). Patients were followed for a minimum of 7 years and a maximum of 12 years.
In the placebo group, 529 men developed prostate cancer. However, in the group of patients taking only vitamin E, 620 men developed prostate cancer (hazard ratio, 1.17; 99% CI, 1.004-1.36, P
= .008), compared to 575 in the selenium only group and 555 in the selenium plus vitamin E group.
The men taking vitamin E took a 400-unit capsule of the vitamin every day for about 5 years. The recommended dose of vitamin E for an adult is 23 units daily. Other recent studies have linked higher intakes of vitamin E with a number of health issues, including an increased risk of developing heart disease. In this study, those taking the supplement were found to be 17% more likely to develop prostate cancer than those in the placebo group.
“The observed 17% increase in prostate cancer incidence demonstrates the potential for seemingly innocuous yet biologically active substances such as vitamins to cause harm,” the authors wrote. “The lack of benefit from dietary supplementation from 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.”
Prostate cancer is the most common non-skin cancer in American men, affecting approximately 16 out of every 100 men in their lifetime. An estimated 240,000 new cases will be identified in the United States in 2011, and approximately 33,000 prostate cancer-related deaths are projected this year.