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Vitamin
C Can Damage DNA
NEW
YORK (Reuters Health) - Although vitamin C is an essential defender
of body cells, the vitamin can also play a ''dual role'' and,
at times, actually damages cells' genetic material, new research
suggests. Investigators say their findings could help explain
why high-dose vitamin C has so far failed as an experimental cancer
therapy.
In the June
15th issue of Science, researchers at the University of Pennsylvania
in Philadelphia report on their test-tube experiments showing
that vitamin C is capable of giving rise to DNA-damaging substances
called genotoxins.
Previous research
has shown vitamin C can promote DNA damage, but the new research
demonstrates a different avenue the vitamin can take in doing
harm.
Moreover,
according to Ian A. Blair and his colleagues, the findings may
offer one reason why vitamin C has failed to meet the expectations
of some who believe it can help treat cancer.
In the average
person, Blair explained in an interview, vitamin C may regularly
act as both a cell's friend and foe, making a daily megadose of
vitamin C unlikely to fight illness. ''This could be an explanation
for why a good diet is better than taking a single vitamin,''
he said.
But one antioxidant
researcher said that while these are ''interesting'' findings
from an ``elegant'' study, it would be wrong to base dietary recommendations
on chemistry experiments.
``This is
quite consistent with what we know about the chemical nature of
vitamin C,'' Dr. Jeffrey Blumberg of Tufts University in Boston,
Massachusetts, told Reuters Health. But, he said, there is ``little
evidence'' that these harmful effects of vitamin C are actually
going on in the body.
What's more,
a significant number of studies have shown vitamin C to either
have no effect or a positive impact on DNA, according to Blumberg.
``You have
to be careful about using this study to make conclusions about
how much vitamin C a person should consume,'' he said in an interview.
As an antioxidant,
vitamin C helps neutralize cell-damaging free radicals, which
are byproducts of metabolism found throughout the body. Because
of this activity, some scientists have suggested that high doses
of vitamin C might help battle cancer by both protecting healthy
cells from the assaults of cancer treatment and by fighting tumor
cells.
But studies
have not yet borne out this belief, and some research shows that
vitamin C can actually be converted to a pro-oxidant in the body
and promote DNA damage. This new research, Blair told Reuters
Health, demonstrates a different, somewhat indirect, way the vitamin
may do ``bad things.''
The free radicals
that vitamin C normally combats can damage DNA directly or by
converting certain fatty acids into genotoxins. Blair's team found
that in the test tube, vitamin C can also give rise to genotoxins
by oxidizing these fats.
According
to the researchers, these findings suggest it will be particularly
important to be on guard for cell damage among participants in
trials using vitamin C as a cancer combatant.
For healthy
people, Blair said, the message echoes tried-and-true nutrition
advice: eat a balanced diet rich in fruits and vegetables rather
than popping a high-dose vitamin C pill, since the vitamin is
no ``magic bullet.''
``If you really
have a good diet...getting about 200 milligrams of vitamin C a
day...I agree,'' Blumberg said. ``But, unfortunately, most people
don't get that.''
The recommended
daily intake for vitamin C is 60 milligrams, but Blumberg said
up to about 250 milligrams can be safely absorbed and used by
the body. Beyond that point, excess amounts will likely be excreted.
SOURCE:
Science 2001;292:2083-2086.
Reference
Source 89
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