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Vitamin E and Colon Cancer - National Institute of
NIH NEWS & FEATURES
High Vitamin E Intake May Help Thwart Colon Cancer
By Jan Ehrman
Adding to the growing body of evidence on the beneficial
effects of vitamin E, scientists supported by NIH's National
Cancer Institute (NCI) have recently determined that large,
supplemental amounts of the antioxidant may help prevent colon
cancer, especially in women under age 65.
Colon cancer is the second leading cause of cancer death in
the United States. It is not known, specifically, what causes the
disease, but dietary factors have been implicated.
The recent findings were gleaned from a comprehensive study
of thousands of women participating in the Iowa Women's Health
Study Cohort, part of a larger NCI-funded prospective study of
breast cancer.
"Surprisingly, perhaps, ours is one of the few
investigations to assess the independent effects of vitamin E on
the development of colon cancer," says Dr. Roberd M. Bostick, the
lead researcher from the University of Minnesota in Minneapolis.
Vitamin E, or alpha-tocopherol, is an antioxidant
(protective substance) found in foods such as sunflower seeds,
nuts, leafy green vegetables, and some vegetable oils. Since many
individuals consume very little dietary vitamin E, in some cases
less than the recommended daily allowance (RDA) of 30
international units (IU), some people believe that supplements
may be useful. Anticipating its benefits, consumers have begun
augmenting their diets with the vitamin for its potential
protective edge against cancer and heart disease.
Besides vitamin E, vitamin C, beta-carotene (a vitamin A
derivative), and some minerals are also antioxidants. These
nutrients help protect the body against destructive substances
such as free radicals, which may transform a cell from normal to
cancerous. Vitamin E and the other antioxidants appear to trap or
neutralize the activity of free radicals, and thus may be useful
in cancer prevention. In an earlier study, NCI scientists
reported a link between vitamin E consumption and lowered oral
cancer risk (Gridley, et al., American Journal of Epidemiology,
May 15, 1992).
Can vitamin E also thwart or at least delay the onset of
colon cancer, a disease that took the lives of more than 48,000
Americans in 1991? The answer appears to be yes, according to the
University of Minnesota researchers.
Bostick and his colleagues investigated whether large
amounts of antioxidants, including vitamin E, had an impact on
the development of colon cancer among 35,000 women, aged 55-69.
The scientists reviewed the subjects' dietary questionnaires
which provided information on food intake, and vitamin and
mineral use. In a retrospective review of the participant?s
health records, they cited 212 cases of colon cancer that had
developed during the 5-year follow-up period. The researchers
discovered that those who had developed colon cancer reported
significantly lower intakes of vitamin E (dietary and
supplemental E combined) than women who remained free of the
disease.
"After adjusting for age, we found a strong link between
vitamin E and the incidence of colon cancer," says Bostick. "Most
notably, we saw a big jump in the decrease of colon cancer at a
daily intake of just 30 IUs." "Further," he added, "the risk
decreased progressively as the amount of vitamin E intake
increased." The effects were most apparent in women younger than
65.
How does vitamin E suppress colon cancer? There are several
intriguing theories, according to the researcher. As noted,
antioxidant micronutrients such as vitamin E may shield against
cell-damaging free radicals, but the vitamin may also stimulate
and enhance the immune system to attack budding cancer cells.
Finally, says Bostick, vitamin E may inhibit the production of
nitrosamines, byproducts of nitrites which are used as common
food preservatives. Nitrosamines have been shown to cause tumors
in lab animals and, in large amounts, may do the same in humans,
experts believe.
Despite the research team's findings, Bostick stops short of
saying that everyone, even persons with risk factors for colon
cancer (e.g., a family history of the disease) should be
consuming supplemental vitamin E. "It would be nice to make that
recommendation. And although we now have animal as well as some
epidemiological evidence to support it, it's still a little
early," he contends.
In the meantime, however, the researcher/physician strongly
encourages individuals to bolster their intake of vitamin E-rich
foods, and also to follow a low-fat, high-fiber,
high-vegetable-and-fruit diet, and get regular physical activity,
measures which themselves may minimize the risk for developing
colon cancer.
This study was published in the September 15, 1993 issue of
Cancer Research.
For more information on cancer, contact: Information Office,
National Cancer Institute, NIH, 9000 Rockville Pike, Building 31,
Room 10A-18, Bethesda, MD, 20892, phone: (301) 496-5583.
Jan Ehrman is editor of NIH News and Features.
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