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De:
"Luiz Meira" <luizmeira@yahoo.com>
Data: Sex Jun 22, 2001 1:06
am
Assunto: Selenio, selênio
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-----Mensagem Original-----
De: "Gabriela" <puertadelsol@telpin.com.ar>
Para: <ALT_HEP_C@yahoogroups.com>
Enviada em: quinta-feira, 21 de junho de 2001 21:43
Assunto: [ALT_HEP_C] Deficiencia de selenio y mutacion viral
Wednesday June 20 10:38 PM ET
Selenium Research Points to Curative Powers
By Carole Vaporean
NEW YORK (Reuters) - Once thought to be a deadly carcinogen, selenium is now
seen as a new wonder mineral that lists cancer prevention, AIDS (news - web
sites) suppression, and anti-aging among its numerous benefits to humans and
animals.
Selenium has been recognized as an essential micro-nutrient for over 40
years, but only since the 1990s has research broadened awareness of its
curative powers in areas as diverse as immune system enhancement, virology,
arthritis and coronary disease, according to the Selenium-Tellurium
Development Association, an international trade group.
Although selenium's future seems bright, many confirmation studies are still
needed to prove its potential benefits, some of which remain in the
theoretical stage. There is also contention over correct dosages, and
uncertainties over which compounds are most effective for its various
applications.
Medical and agricultural uses account for only five percent of annual
selenium demand, but is a major area of research on the mineral that has
been growing that sector's share.
About 5,000 research papers on this metalloid are produced each year, and
the U.S. National Institute of Health (NIH) has taken their findings
seriously enough to fund new research that expands on the positive results
achieved so far.
The basic element selenium, named for the Greek moon goddess, is not useful
to the body. However, as part of an organic molecule, like a selenoprotein,
it can save lives.
Discovered in 1817 by a Swedish chemistry professor Berzelius, selenium is
widely dispersed in the earth's crust and is derived as a by-product of
copper refinery. About 200 tons of copper ore typically yield one pound of
selenium.
As a food source, selenium is abundant in meats, fish, grains, and Brazil
nuts, but amounts vary with the local soil.
CANCER PREVENTION
Cornell University professor Gerald Combs Jr. said there has often been a
``fairy dust dimension'' attached to selenium, in being touted as a
cure-all.
But, in the last 20 years, research has ``overwhelmingly'' demonstrated its
cancer prevention abilities, and in some cases that it can even result in
the disappearance of the existing disease, said Texas Tech University
researcher Julian Spallholz.
Several recent patent applications for selenium compounds demonstrated their
therapeutic abilities when injected into a tumor, or their ability to
inhibit cancer cell growth, which offers promise of targeting specific
cancers, he said.
Prior to the last 20 years, however, many scientists thought selenium a
deadly carcinogen. Experiments to prove it so with rats were inconclusive
and sometimes unsuccessful.
In 1996, the work published by Cornell's Combs with the late Dr. Larry Clark
now serves as the landmark study that establishes selenium as an
anti-carcinogen in humans.
Their 10-year study of 1,312 participants found selenium takers had 37
percent fewer instances of new cancers, and less than half the cancer deaths
as placebo takers.
Specifically, Clark found the incidence of prostate cancer was halved with
selenium supplements of just 200 micrograms a day. Lung and colon cancer
rates fell 38 percent.
CRITICS
Critics contest the results on the formal grounds that they have not yet
been confirmed, and that the researchers had not set out originally to test
for prostate and lung cancers.
Furthermore, selenium proved ineffective against skin cancers, for which the
subjects had been selected.
At a minimum, the study sparked a surge of interest in selenium that
generated funding for follow-up research.
The National Cancer Institute (news - web sites) is funding a 32,000 man,
12-year study of prostate cancer. That program is still in the recruiting
stage, which began last October. The NIH has also put up the money for a
colon cancer study.
Both tests will use 200 microgram supplements. One reason is the cost of
paying for 32,000 daily doses. Another is to comply with official
Recommended Daily Allowances, even though many experts find a 200 microgram
dose to be conservative.
For example, Inuit Eskimos in Greenland were tested for selenium
concentrations in their blood. Their diets, rich in selenium from the marine
animals they eat, had levels as high as 4,400 micrograms. Yet, only mild
signs of selenosis, or selenium toxicity, appeared as striated fingernails.
Despite dosage being one of the hotly debated areas surrounding selenium,
Combs, who has investigated the topic, said no one is currently proposing a
multiple dose study.
Over exposure to selenium is more poisonous than either mercury or arsenic,
and can cause gastrointestinal problems, hair loss, and mild nerve damage.
Testing for levels of toxicity could be problematic, said Combs.
By knowing minimum dosages, he added, you can give dietary advice, put it in
food, and have the food industry be a participant in disseminating it to the
public.
Experts say no one would overdose from the revised official upper limit of
400 micrograms a day. Even with selenium in a normal diet, they said, there
is no risk of overdosing.
Results of deficiency are clear in places like China and New Zealand where
soil levels are low in the trace mineral. Deficient populations develop
muscle disease, infertility, heart disease, thyroid problems, and other
negative symptoms.
University of North Carolina professor Melinda Beck found that Chinese
children who lacked the mineral had a far higher incidence of a heart
ailment known as Keshan disease. Giving them dietary supplements largely
eradicated the illness.
Beck's latest research released last week goes a step further. She found
that the human influenza virus mutates into more virulent forms and that
mutation accelerates when selenium is deficient in mice.
Beck said she believes that a similar mutation process probably occurs in
humans. She also extrapolates her findings to other RNA viruses, including
hepatitis, Ebola (news - web sites), and human immunodeficiency virus (HIV
(news - web sites)). Her next step is to test her theories on the AIDS
virus, she said.
``We found that even mice with normal nutrition are more susceptible to the
newly virulent strains,'' said Beck.
That means that in a highly mobile population, a selenium deficient infected
person can spread more virulent forms of a disease even to those who are
currently healthy, she said.
These findings make determining dosage more urgent for wider dissemination.
Cancer researchers are also examining how much selenium is needed to act as
an anti-carcinogen.
Several population studies have shown that people with higher blood levels
of selenium have fewer incidents of cancer even among groups with adequate
amounts in their diet, wrote Dr. Richard Passwater, who has studied selenium
for 40 years, in the May 2001 edition of Whole Foods magazine.
HIV researchers are also exploring what levels of selenium are needed to
inhibit the replication of the HIV virus (news - web sites), and to
counteract the debilitating effects of AIDS.
Marianna Baum's oft-sited 1997 clinical study at the University of Miami
indicated that selenium deficiency is a predictor of survival for those with
HIV-1 infection.
Baum recently won NIH approval for a follow-up study to determine whether
selenium may actually slow the progress of AIDS. The NIH is currently
considering funding for the study.
While no one is sure of exactly how selenium inhibits HIV, its performance
as an antioxidant enzyme that protects cells against damage from free
radicals is well-known. It is also essential for normal immune system and
thyroid functioning.
AIDS-related malabsorption can deplete levels of many nutrients needed to
enhance the immune system. But, selenium may also be needed by HIV itself
for replication, which could deplete selenium levels in the host, according
to the NIH.
In an interview for Whole Foods magazine last year, Dr. Will Taylor at the
University of Georgia said his analysis of the HIV genetic code suggests
that the progression of AIDS could be slowed by providing adequate selenium
to the virus, so that it does not replicate in high numbers and invade other
cells when seeking its needed selenium.
``Until we verify the precise role of selenium in AIDS, I'd rather be
optimistic and hope that having HIV is not a death sentence to its
carriers,'' said Taylor.
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