Quality survey Health benefits Safety Reading labels Ask the supplier Standards & regulations


Testing news
Ask the expert
Contact us
Privacy policy

Headline News

Vitamin C and DNA Damage: Real Danger or False Alarm?
24 July 2001
by Wyn Snow, Managing Editor

Once 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:

Vitamin C Supplements May Be Harmful -- from ABCnews.com

Vitamin C Can Damage DNA, Study Shows -- from Reuters Health (Yahoo news)

Vitamin C Found to Promote Cancer-Causing Agents -- from Reuters (Yahoo news)

Vitamin C May Be Two-Edged Sword -- from HealthSCOUT.com

and even that source of all the news that's fit to print, The New York Times, said:

Vitamin C Pills Tied to DNA Risk -- from NYTimes.com

It 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?

Study looked at vitamin C in test tube

It 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.

The 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."

To 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.)

Test tube results not always relevant to living cells

The 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 ways:

The study used a concentration of fat molecules that is approximately 10,000 times more intense than has ever been found in a living body.

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.)

Perhaps 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 never coexist!

Similar controversy emerged in 1998

In 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.

The 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.

Many 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!

Bruce 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.

Evidence leans toward vitamin C as cancer-fighter

According 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 benefit.

Diets 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!

Vitamin 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.


This year's study concerning vitamin C and DNA was published in Science, Vol 292, pages 2083-2086, 15 June 2001. www.sciencemag.org.

News 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.]

Information 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.

Linus 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.

David Stauth. "Indictment of Vitamin C Questionable, Expert Says." Linus Pauling Institute, 6 July 2001. www.orst.edu/dept/lpi/new/atherosclerosis.html.

The 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.

Information 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.

Balz 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.

Life 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.end-of-story




Health benefits Safety Reading labels Ask the supplier Standards & regulations Contact us

(c) Copyright 1999-2003 Dietary Supplement Quality Initiative. For permission to reprint, please contact our editor.