Selenium May Reduce Colon Cancer Risk
High levels of selenium in the blood
may reduce the risk of colorectal cancer, according to a new study
that suggests but doesn't prove the mineral's role as a preventive.
Selenium is a trace mineral found
in meats, grains, seafood and some nuts. However, how much you
get varies according to where you live, because different areas
have different concentrations of selenium in the soil. Those who
live in areas where selenium intake is low have higher rates of
colorectal and other cancers.
"Your risk of colorectal cancer
can vary by the amount of selenium you consume," said lead
researcher Elizabeth T. Jacobs, from the Arizona Cancer Center.
"People with higher blood selenium levels tended to have
a decreased risk of a recurrence of colon cancer."
Selenium may protect against not
only colon cancer but also prostate cancer and lung cancer, Jacobs
Jacobs and her colleagues collected
data from three randomized trials of colon cancer patients: the
Wheat Bran Fiber Trial, the Polyp Prevention Trial and the Polyp
Prevention Study. Looking at the data from these trials, they
were able to determine the effect of selenium in the development
of new cancerous colon polyps in patients.
The researchers found that those
with the highest selenium levels had a 34 percent lower risk of
developing a new colon cancer, compared with those who had the
lowest selenium levels. Their report appears in the Nov. 17 issue
of the Journal of the National Cancer Institute.
Whether increasing your selenium
intake will actually be beneficial is not clear. Jacobs said that
increasing selenium consumption will help people who have low
levels of the element. "It will benefit those whose intake
of selenium is low," she said. "However, it may not
benefit those who already have adequate selenium levels."
The risks of having too much selenium
are not known but are being studied, Jacobs said. In addition,
studies are under way to determine the optimum selenium levels
needed to prevent colon cancer and prostate cancer.
Jacobs also said there are ongoing
studies to see if selenium can help treat patients with prostate
"Selenium is a promising preventive
agent for colorectal cancer, but we are hopefully going to confirm
this," Jacobs said.
"This study is not definitive,"
said Dr. Scott M. Lippman, chairman of the department of clinical
cancer prevention at the University of Texas M.D. Anderson Cancer
Center, "because it is not from a large randomized control
trial of selenium."
Based on this study, Lippman believes
that such trials should be done to test the benefit of selenium
in preventing colon cancer. Data from ongoing trials may provide
an answer, he said: "I believe that over the next five to
10 years, we will have some very compelling data one way or the
other regarding selenium's ability to suppress colorectal cancer."
Lippman, who co-wrote an accompanying
journal editorial, said there are biological reasons that may
make selenium effective in preventing colon cancer. "There
is laboratory information that suggests that selenium might prevent
colorectal cancer," he said.
One of these mechanisms is selenium's
role in turning on genes that prevent cancer. Another is the mineral's
effect in altering the metabolism of polyunsaturated fatty acids
found in red meats, which are involved in the development of colorectal
cancer, Lippman said.
"Not only are the epidemiological
data very consistent and supportive, but there are actually fairly
strong biologic plausibility for selenium's ability to protect
against colorectal cancer," he said.
However, Lippman cautioned that
the results of this study do not mean that people should start
taking selenium supplements in the hope of preventing cancers.
"The epidemiological and biological data strongly support
going to the next step of a definitive randomized trial to find
out if in fact it does work," he said.
information on Selenium
Reference Source 101
November 17, 2004