C and DNA Damage: Real Danger or False Alarm?
Wyn Snow, Managing Editor
again, headlines are suggesting that taking vitamin C supplements
could pose a health risk, but surprisingly, behind the headlines
is the fact that this "health risk" is based on the results of one
study (published in Science on 15 June 2001). Here's how
major media outlets played the story:
C Supplements May Be Harmful -- from ABCnews.com
C Can Damage DNA, Study Shows -- from Reuters Health (Yahoo
C Found to Promote Cancer-Causing Agents -- from Reuters (Yahoo
C May Be Two-Edged Sword -- from HealthSCOUT.com
even that source of all the news that's fit to print, The
New York Times, said:
C Pills Tied to DNA Risk -- from NYTimes.com
seems a safe bet that most Americans saw at least one of these reports.
But are the headlines right? Are we risking DNA damage by taking
vitamin C supplements?
looked at vitamin C in test tube
turns out that the Science study is of general interest,
if only for the way it shows how vitamin C behaves in a test tube
under unusual conditions. But that has almost no relevance to what
happens inside a living body.
study's lead author, Ian Blair PhD, tried to calm the media reports.
In an interview with Better Nutrition magazine, Blair said,
"The study is being over-interpreted. I've been trying to de-sensationalize
the paper by referring people to other studies that have not found
direct evidence of vitamin C supplementation preventing cancer."
Also, Reuters said that Blair told them, "Absolutely for God's sake
don't say vitamin C causes cancer."
answer concerns raised by these headlines, SupplementQuality.com
went to the world leaders in vitamin C research: the Linus Pauling
Institute at Oregon State University. They had already posted an
analysis of the Science article on their website. We summarize
their points here. (See also the link to their full analysis in
our list of Sources, below.)
tube results not always relevant to living cells
Science study created an environment in a test tube -- combining
vitamin C with rancid (oxidized) fat molecules. Any test tube situation
is relevant to human biochemistry only insofar as it mimics the
conditions inside a living cell. The test-tube setting of this study
varied significantly from in vivo conditions in several important
study used a concentration of fat molecules that is approximately
10,000 times more intense than has ever been found in a living
cells also contain enzymes that change rancid fat molecules into
harmless "alcohols" within a fraction of a second -- which means
that the fat molecules are no longer "there" to react with any
vitamin C that is also in the cell. (In the Science study,
the interaction between vitamin C and fat molecules was conducted
over a two-hour period.)
most telling of all, studies at the Linus Pauling Institute have
shown that fat molecules in blood serum don't become rancid until
vitamin C has been exhausted. In other words, vitamin C protects
fat molecules from becoming rancid in the first place -- so they
controversy emerged in 1998
1998, a team of British scientists at the University of Leicester
gave 500 mg of vitamin C to 30 healthy subjects every day for six
weeks. They then examined two markers of DNA damage in the blood
of their subjects -- finding that one went up while the other went
down -- and published this finding in the Correspondence section
of Nature on 9 April 1998. This report also made headlines
as "Vitamin C Can Cause Cancer" -- and was soon heavily critiqued
by other vitamin C researchers.
controversy exists because vitamin C -- like other antioxidants
-- becomes a weak free radical (or pro-oxidant) right after it neutralizes
a dangerous free radical. At this stage, vitamin C and other antioxidants
do have the capacity to damage DNA. However, antioxidants work together
to restore each other back into fully potent antioxidants, so this
weak free radical stage is very brief.
methodological problems were present in the research reported in
Nature. At the very least, there are roughly twenty markers
for DNA damage that are appropriate to examine. Of the two that
the British researchers looked at, the marker that went down is
some 10 times more dangerous than the one that went up. Also, the
methodology they used to extract DNA from the cells is known to
produce false results!
N. Ames, PhD, of the University of California, Berkeley, one of
the world's most distinguished scientists, bluntly characterized
the Nature research as "bad science." Ames also notes that
roughly half of all chemicals, both synthetic and natural, cause
DNA damage -- including compounds found in most fruits and vegetables.
However, the friendly chemicals in these substances far outweigh
the dangerous ones; the preponderance of research finds that eating
more fruits and vegetables is beneficial to our health.
leans toward vitamin C as cancer-fighter
to the Linus Pauling Institute, many animal and cell culture studies
have shown anti-cancer effects of vitamin C. The vitamin has also
been used therapeutically in human cancer patients with some apparent
rich in vitamin C lower the risk of cancer, heart disease, stroke
and other chronic degenerative diseases. Also, the body does not
distinguish between vitamin C from fruits and vegetables and the
synthetic form found in supplements. The bottom line? Evidence indicates
that you will do yourself a lot of good by taking vitamin C supplements,
and certainly no harm!
C is one of the safest supplements. How much to take, however, is
a controversial question. The RDA is set at 90 mg/day for men and
75 mg/day for women. According to the federal Institute of Medicine,
healthy adults can safely consume as much as 2,000 mg/day; some
experts believe the safe upper level is considerably higher.
year's study concerning vitamin C and DNA was published in Science,
Vol 292, pages 2083-2086, 15 June 2001. www.sciencemag.org.
about this study appeared in many publications and websites, as
summarized at the top of this article; the following ABCNEWS.com
story is typical: ABCNEWS.com. "Vitamin C Supplements May Be Harmful."
ABCNEWS.com website, 15 June 2001. [link to article has expired.]
criticizing this study was found in: Natural Products Insider.
"Vitamin C and DNA Damage Incorrectly Linked." Natural Products
Insider website, 15 June 2001. www.naturalproductsinsider.com/hotnews/16h151622.html.
Pauling Institute. "Does Vitamin C Cause Cancer - or Here We Go
Again!" Linus Pauling Institute website, 15 June 2001. osu.orst.edu/dept/lpi/new/vitamincancer2.html.
Stauth. "Indictment of Vitamin C Questionable, Expert Says." Linus
Pauling Institute, 6 July 2001. www.orst.edu/dept/lpi/new/atherosclerosis.html.
other study about vitamin C and DNA was Ian D. Podmore et al, "Vitamin
C exhibits pro-oxidant properties," Nature, Vol 392, page
559, 9 April 1998.
criticizing this study and describing details of how vitamin C performs
as an antioxidant was found in: Jack Challem. "Vitamin C? Gene damage?
How do you make sense of the research?" Commentary on his website,
12 April 1998. www.thenutritionreporter.com/vita-c.html.
Frei, PhD, in an interview with Richard A. Passwater. "New Research
Findings On Vitamin C Safety: An interview with Dr. Balz Frei. Part
1: The Pro-Oxidant Myth." Dr. Frei is one of the world's leading
researchers in vitamin C; this interview was published in Whole
Foods Magazine, 1998.
Extension Foundation. "Life Extension Foundation's Updated Vitamin
C Rebuttal." Life Extension Foundation website, 14 April 1998. www.lef.org/magazine/articles/vitc_damage2.html.