Selenium supplements can reduce cancer rates, new study shows
FOR RELEASE: Jan. 7, 1997
Contact: Susan Lang
Office: (607) 255-3613
E-Mail: SSL4@cornell.edu
ITHACA, N.Y. -- Men and women taking selenium supplements for 10 years had
41 percent less total cancer than those taking a placebo, a new study by
Cornell University and the University of Arizona shows. "Although
more than a hundred of animal and dozens of epidemiological studies have
linked high selenium status and cancer risk, this is the first
double-blind, placebo-controlled cancer prevention study with humans that
directly supports the thesis that a nutritional supplement of selenium, as
a single agent, can reduce the risk of cancer," said Gerald F. Combs
Jr., a nutritional biochemist and Cornell professor of nutritional
sciences.
Combs and a group of co-authors reported their findings in the Jan. 1,
1997 issue of The Journal of the American Medical Association. The senior
author is epidemiologist Larry Clark, who was at Cornell at the onset of
the study and is now at the Department of Family and Community Medicine at
the University of Arizona School of Medicine.
The other primary authors are Cornell biostatisticians Bruce W.
Turnbull and Elizabeth Slate, professor and assistant professor,
respectively, in the School of Operations Research and Industrial
Engineering, and David S. Alberts, M.D., of the College of Medicine,
Arizona Cancer Center.
In 1983, the researchers recruited 1,312 randomized patients with
histories of skin cancer at seven dermatology clinics located in
low-selenium areas of the United States (Augusta and Macon, Ga., Columbia,
S.C., Wilson and Greenville, S.C., Miami, and Newington, Conn., where
consumers ingest an average of about 100 micrograms of selenium a day).
The patients were given either a placebo or a 200-microgram daily
supplement of selenium (twice the average amount these Americans consume
in their diet, thereby tripling their selenium intake).
Skin cancer patients were chosen because they have a 25 percent annual
chance of a recurrence, and skin cancer is easy to diagnose and can be
quickly treated. The researchers set out to determine whether they could
reduce the average recurrence rate with selenium supplements.
Ironically, 10 years later, the results were not significant for skin
cancer. However, they were "compelling" for overall cancer
incidence and mortality rates, Combs stressed. Of the selenium group, 69
developed some type of cancer compared with 116 of the placebo group; 28
of the selenium patients died of cancer compared with 58 from the placebo
group.
"Overall, the selenium group experienced 18 percent less mortality
than the placebo group, and almost all of that difference was due to some
form of cancer," said Combs, who credits Cornell with having the
longest history of research in selenium nutrition research in the world.
"This is the first time anyone has shown that any single nutrient can
result in such a reduction in cancer risk. The fact that we saw a pattern
in lower incidence and mortality rates across all the clinics gives us
even greater confidence in these findings."
Prostate, esophageal, colorectal and lung cancer rates were among the
most dramatic: patients in the selenium group had 71 percent, 67 percent,
62 and 46 percent reductions in cancer rates, respectively, than the
placebo group.
The current Dietary Guidelines now recommend that men consume 70
micrograms of selenium a day and women 55 micrograms; Americans typically
get between 100 to 160 micrograms a day in their diets, Combs said.
Selenium blood levels vary widely in populations. Even Americans with
the lowest selenium intake of 60 to 80 micrograms per day -- those living
along the Southeastern seaboard and in the Pacific Northwest -- ingest two
to five times more than citizens of New Zealand and 10 to 20 times more
than people living in some areas of China. Selenium blood levels vary
among populations largely because of wide differences in soil, agronomic
practices, food availability and preferences and methods of food
preparation.
Although a 1995 Harvard University study of more than 62,000 nurses
reported no anti-cancer benefits of selenium, Combs said that the
researchers measured selenium in the toenail clippings of the nurses.
"This method presumes that the concentration of selenium in nails
accurately correlates with metabolic selenium status in the body,"
Combs pointed out. "There is no evidence for that."
The University of Arizona-Cornell research team reported in 1991 that
low selenium levels in the blood were linked to increased risk of
neoplastic polyps in the colon, a precursor to colorectal cancer. And in
other studies at Cornell, colleagues of Combs' reported in 1995 that
animals fed diets high in selenium had 50 percent fewer tumors than those
fed diets of average selenium content.
Combs is not recommending the use of oral supplements of selenium;
however, he does emphasize the importance of consuming low-fat diets that
are adequate in selenium and are balanced with respect to other essential
nutrients. The most important dietary sources of selenium are meats, fish
and cereals; dairy products and eggs contribute significant amounts. Some
nuts can also be high in selenium if they were grown in high-selenium
areas.
Of the 40 nutrients currently recognized as essential for human
nutrition, selenium was the last to be recognized in 1957. A key component
for at least two essential enzymes, selenium provides the body with
antioxidant protection in concert with vitamin E and is required for
normal thyroid hormone metabolism.
The study was funded in part by grants from the American Institute of
Cancer Research, the American Cancer Society and the National Institutes
of Health.
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