Vitamin C exhibits pro-oxidant properties. Nature 1998; 392

This forum will focus on analyzing recent clinical studies of vitamin C.

Moderator: ofonorow

davidshields

Vitamin C exhibits pro-oxidant properties. Nature 1998; 392

Post Number:#1  Post by davidshields » Sun Jul 30, 2006 5:01 pm

This is a fairly old study, but in light of the more recent findings about pro-oxidant properties (and unexpectedly bad effects on health) of various antioxidant supplements, I wanted to investigate further. However, a search on this forum does not return much for "pro-oxidant". What are the vitamin C experts saying about this pro-oxidant activity and DNA damage?

Here is a summary from one article:
Intakes of vitamin C below the recommended daily allowance are associated with increased free-radical damage to DNA4,11 but, paradoxically, so is supplementation with high-dose vitamin C.

Here are the references for that statement:

* Podmore ID, Griffiths HR, Herbert KE, Mistry N, Mistry P, Lunec J.
Vitamin C exhibits pro-oxidant properties. Nature 1998; 392: 559.

* Rehman A, Collis CS, Yang M, et al. The effects of iron and vitamin C
co-supplementation on oxidative damage to DNA in healthy volunteers.
Biochem Biophys Res Commun 1998; 246: 293–98.

* Beatty ER, England TG, Geissler CA, Aruoma OI, Halliwell B. Effects
of antioxidant vitamin supplementation on markers of DNA damage and
plasma antioxidants. Proc Nutr Soc 1999; 58 (abstr): 44.

davidshields

Post Number:#2  Post by davidshields » Sun Jul 30, 2006 5:20 pm

Interesting reading on this topic:
http://lpi.oregonstate.edu/news/beckman.html

(However, I would still appreciate informed opinions from readers of Vitamin C Foundation forum. Thanks.)

From the link:
It appears, therefore, that the oxidative DNA adducts measured by Podmore et al.1 do not accurately reflect DNA damage in vivo. It is likely that >90% of the DNA adducts were formed ex vivo. The elucidation of ascorbate's in vivo effects on oxidative DNA damage has to rely on more definitive methodologies and more thorough experimentation. In addition, the value of ascorbate as an antioxidant and for human health does not rest on a few measurements of oxidative DNA damage, but rather is supported by hundreds of biochemical, cellular, physiological, nutritional and epidemiological studies18. It would be as unwise to recommend vitamin C supplementation based on a single measurement of decreased oxidative DNA damage as it is to discourage its use based upon this study1.

In conclusion, we believe that the results presented are an ex vivo artifact, given the high values obtained. In the context of the huge literature supporting the health benefits of vitamin C, the conclusions of the study are unwarranted.

davidshields

Post Number:#3  Post by davidshields » Sun Jul 30, 2006 5:25 pm

Here is another good link on this topic:

http://www.thorne.com/pdf/journal/3-3/editorial3-3b.pdf


Jeffrey S. Bland, Ph.D.

The paper entitled, "Vitamin C Exhibits Pro-oxidant Properties," which appeared recently in the journal Nature has attracted considerable attention. Authors Podmore, Griffiths, Herbert, et al describe the potential pro-oxidant effects of daily supplementation with 500 mg of vitamin C on DNA base oxidation in vivo. 1 Their conclusion raises concern because a vast number of individuals regularly supplement their diets with vitamin C in the belief that it has antioxidant effects.

The results of the study are paradoxical. The authors found that the oxidation of guanine (a purine) in DNA was significantly reduced after vitamin C supplementation, but the oxidation of adenine (also a purine) was significantly elevated. The oxidation of nucleic acids is indicative of oxidative stress being placed on DNA with the concomitant exposure to reactive oxygen species, such as hydroxyl radical. The oxidation of adenine suggests that vitamin C (supplemented at 500 mg) participated as a pro-oxidant, whereas the reduced level in the oxidation of guanine suggests it acted as an antioxidant.

Is vitamin C a pro-oxidant or an antioxidant? The answer to this question is not available from the data or its interpretation in the paper. The results are contradictory. The failure of the authors to point out this paradox in the conclusions drawn from their work is a significant oversight. They focus solely on the oxidation of adenine, and conclude that a supplement of 500 mg vitamin C acts as a pro-oxidant, while ignoring the observed antioxidant effects with regard to guanine. It is certainly well established that vitamin C can serve as a pro-oxidant through formation of ascorbyl radical. It is also known this radical is quenched by vitamin E to yield tocopheryl radical, which, in turn is reduced by the conversion of glutathione to oxidized glutathione. High doses of vitamin C could increase the concentration of ascorbyl radical that, if not quenched by vitamin E, could result in an increased oxidant burden. The observation in the Podmore et al study that guanine oxidation was reduced with supplementation of 500 mg vitamin C strongly suggests this was not the case. The presence of oxidized adenine remains a contradiction.

It has recently been pointed out that adenine is easily oxidized in the extraction procedure of lymphocytes for DNA. 2 Therefore, it is possible that the observed adenine oxidation was not a result of vitamin C intake, but rather a result of experimental techniques used in the extraction of the DNA. Although the study opens the door for more investigation, it should not lead to the conclusion that a supplement of 500 mg vitamin C is dangerous. Until the apparent contradiction in the data relative to the oxidation of adenine versus the antioxidation of guanine is resolved, this paper simply represents an interesting observation in the absence of replication or mechanistic understanding.

References

1. Podmore ID, Griffiths HR, Herbert KE, et al. Vitamin C exhibits pro-oxidant properties. Nature 1998;392:559.

2. Jenner A, England TG, Aruoma OI, Halliwell B. Measurement of oxidative DNA damage by gas chromatography­mass spectrometry: ethanethiol prevents artifactual generation of oxidized DNA bases. Biochem J 1998;331:365-369.

ofonorow
Ascorbate Wizard
Ascorbate Wizard
Posts: 15822
Joined: Tue Nov 22, 2005 3:16 pm
Location: Lisle, IL
Contact:

History

Post Number:#4  Post by ofonorow » Mon Jul 31, 2006 11:03 am

Thank you for bringing this up at the forum, as it has probably not been addressed here. The Foundation addressed this pseudo issue years ago, after the first publication in Nature cited above - which has since been retracted by the authros without publicity!

In review, a "bomb" was dropped that generated world-wide publicity. The bomb was based on a letter to Nature (not a peer revied study) regarding in vitro (test tube) experiments with an obscure indicator of oxidation. Later, the authors retracted their findings, with little or no publicity.

The fact is that vitamin C has both pro-oxidant and anti-oxidant effects in the body, as Pauling summarizes in HOW TO LIVE LONGER AND FEEL BETTER (1986, 2006)

The pro oxidant effects are utilized by our immune systems, for example.

But vitamin C is the primary water soluble antioxidant. If you are seriously worried about taking so-called "high" dose of vitamin C, then you have to ask your self why all other animals produce 3000 to 13000 mg (adjusted for body weight) 24/7.
Owen R. Fonorow
HeartCURE.Info
American Scientist's Invention Could Prevent 350,000 Heart Bypass Operations a year

Bobber
Enthusiast
Enthusiast
Posts: 140
Joined: Wed Nov 23, 2005 11:14 am
Location: Mid West
Contact:

More

Post Number:#5  Post by Bobber » Tue Aug 01, 2006 9:29 am

Cathcart also has This PDF document on his web site which deals with this topic.
Bobber

joiv
Vitamin C Master
Vitamin C Master
Posts: 367
Joined: Thu Jun 08, 2006 2:21 pm
Location: Norway
Contact:

Post Number:#6  Post by joiv » Mon Aug 21, 2006 1:33 pm

"Ascorbate does not act as a pro-oxidant towards lipids and proteins in human plasma exposed to redox-active transition metal ions and hydrogen peroxide."
http://www.ncbi.nlm.nih.gov/entrez/quer ... s=12726918 8)


Return to “Clinical Studies”

Who is online

Users browsing this forum: No registered users and 18 guests