Vitamin E Does Not Protect Women Against CancerKey Words
Vitamin E, dietary supplements, prevention. (Definitions of many terms related to cancer can be found in the Cancer.gov Dictionary.)
Summary
Vitamin E supplements do not protect healthy women age 45 or older against cancer, according to the 10-year, randomized Women’s Health Study. However, it remains unclear whether vitamin E might yet prove protective in other groups of people.
Source
Journal of the American Medical Association, July 6, 2005 (see the journal abstract).
Background
Vitamin E has been shown to have antioxidant properties. Antioxidants are substances that may protect cells from cancer-causing damage; indeed, considerable laboratory evidence indicates that antioxidants may slow or possibly prevent the development of cancer. However, information from clinical trials, which are studies designed to most reliably answer how well drugs and other interventions work in people, have reached inconsistent conclusions.
In 2003, researchers with a large, long-term trial involving male smokers reported that participants who took a daily vitamin E pill were less likely to develop or die from prostate cancer than those taking a placebo (dummy pill); however, vitamin E failed to protect against lung cancer (see the related press release about the ATBC trial). In 2005, researchers with another trial involving men and women with vascular disease or diabetes reported that long-term, daily use of vitamin E failed to reduce the risk of cancer or cancer death (see related press release about the HOPE-TOO trial).
The study described here examined whether regular doses of vitamin E decrease the risk of cancer and cardiovascular disease among healthy women.
The Study
Between 1992 and 2004, researchers with the Women’s Health Study (WHS) enrolled over 39,000 women health professionals at least 45 years of age; the
mean age at the start of the trial was about 54 years. The goal of the study was to investigate the protective effects of low-dose aspirin (100 mg), vitamin E, and beta-carotene on cardiovascular disease and cancer. (The beta-carotene part of the study was stopped early, in 1996, when other studies showed no protection and even a possible risk of cancer.)
Women were randomly assigned to receive aspirin, vitamin E, both, or placebos. Neither they or their doctors knew which group they were in (meaning the study was double-blinded) and all participants were free of disease at the start of the trial. The aspirin and vitamin E aspects of the study were conducted together but analyzed and reported independently. Only the cancer-related vitamin E analysis is described here (see the related Low-Dose Aspirin Fails to Protect Women Against Cancer). A total of 19,937 women took 600 IU of alpha-tocopherol (a form of vitamin E) and 19,939 women took a placebo every other day. The participants were followed for an average of about 10 years.
The lead author for the vitamin E analysis was I-Min Lee, MBBS, ScD of Brigham and Women’s Hospital in Boston, Mass. The study was supported by the National Cancer Institute (NCI) and the National Heart, Lung, and Blood Institute. Medications were provided by Bayer HealthCare and the Natural Source Vitamin E Association.
Results
During the trial, 2,865 women in the vitamin E part of the study developed invasive cancer; that is, cancer that spread beyond the layer of tissue in which it first developed. Of those, 1,437 were in the vitamin E group and 1,428 were in the placebo group. The findings demonstrate no significant difference in cancer rates.
The researchers also analyzed the incidence of certain types of cancer in both the vitamin E and placebo groups: breast cancer (616 cases in the vitamin E group vs. 614 in the placebo group); lung cancer (107 vs. 98); and colon cancer (107 vs. 107). Once again, there was no statistically significant difference: women taking vitamin E were just as likely to develop these cancers as the placebo group.
Findings also showed that cancer death rates were not significantly influenced by the vitamin E supplements. Among the women taking vitamin E, there were 308 cancer deaths, and among those taking a placebo, there were 275.
Comments
According to the authors, “The available data do not provide strong evidence for a role of vitamin E in cancer prevention, particularly in well-nourished women.”
In an accompanying editorial, Eric J. Jacobs, Ph.D., and Michael J. Thun, M.D., of the American Cancer Society, emphasized how strong the study results were. They noted that because of the relatively large size of the trial and the decade-long intervention period, the effects of vitamin E supplementation could be effectively evaluated.
Lori Minasian, M.D., of NCI’s Division of Cancer Prevention, agreed. “This is a very large and well-designed study. The findings demonstrate no benefit of vitamin E supplementation for the prevention of overall cancer or cancer mortality, ” she said. Vitamin E appeared not to cause any significant harm to women taking it, she said. Nonetheless, “there is no compelling reason for healthy women 45 years of age or older to take vitamin E supplements to prevent cancer.
“That is not to say,” she added, “that there isn’t a role for vitamin E supplementation, just that it doesn’t appear to be effective for this population.”
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