Vitamin C

In the news: "Vitamin C causes damage to DNA." True? or not true?

Not true. In this test-tube experiment under artificial conditions, vitamin C combined with rancid fats to form a particular substance. It is possible, the experimenters said, that this substance might react with and damage vitamin C. The newspapers and television people then simplify for you, the public. "Vitamin C can damage your DNA"

How about some details? In the laboratory, they kept vitamin C in contact with the rancid fats for a period of two hours, but in a human, rancid fats are detoxified in less than a second. Vitamin C and rancid fats will never exist together in your body for two hours. In the laboratory under these artificial conditions, they were able to create this substance that they think "might" damage DNA. Did they test to see if this substance actually damaged DNA? Well, no. They "supposed" it.

The chemical environment in humans is much more complex than this simple system set up in a test-tube. Previous tests have shown that in humans, vitamin C prevents damage from rancid fats.

If these investigators are correct in their supposition that vitamin C damages DNA, then vitamin C users should get more cancer than non-users. The fact is, vitamin C users develop cancer less often than non-users.

More about DNA

If you want to understand the details of DNA, we can make it simple.

DNA, we know, is the blueprint, or cookbook, for our body. DNA, like any cookbook, is composed of letters, which are four chemical compounds named guanine, cytosine, adenine, and thymine. Depending on the sequence of these letters, your body knows how to create the proteins that lead to the uniqueness of you. If these compounds are damaged, they become oxidized compounds. For instance, hit guanine with a free radical and you get 8-oxo-2'-deoxyguanosine (8- oxodG). Now you've got an unreadable letter in your cookbook; your DNA is damaged. Since life is one great big free radical war (and we all eventually lose), we all have 8-oxodG in our bodies. Fortunately, we have DNA repair systems. Think of a proofreader, always going through the cookbook and correcting errors. (Too many errors, though, and the proofreader can get confused.)

Studies showing that vitamin C protects DNA

As it turns our, researchers at the Division of Chemical Pathology, Centre for Mechanisms of Human Toxicity, University of Leicester, England, examined levels of 8-oxodG in white blood cell DNA in people taking vitamin C. Guess what? Vitamin C reduced levels of this oxidized form of guanine. You can read it in FEBS Lett (1998 Nov 20;439(3):363-7. Novel repair action of vitamin C upon in vivo oxidative DNA damage.)

Another study, this time from Glasgow University, (published in Am J Clin Nutr 1998 Jun;67(6):1210-8) found that "pretreatment with all flavonoids and vitamin C produced dose-dependent reductions in oxidative DNA damage" caused by hydrogen peroxide.

Another study looked at DNA damage due to the anti-cancer drug doxorubicin. High doses of vitamin C did not increase the DNA damage from doxorubicin, and low doses of vitamin C protected from DNA damage. No dose caused increased damage.

Finally, a report from the journal Cancer Detection and Prevention (2000;24(6):508-23) entitled "New evidence for antioxidant properties of vitamin C" concluded that "doses up to 5,000 mg neither induce mutagenic lesions [did not cause any cell mutation] nor have negative effects on NK cell activity [NK, or Natural Killer, cells protect you from viruses and cancer], apoptosis [this is a built-in capacity for a cell to self-destruct if it is becoming cancerous], or cell cycle [normal cell reproduction was not harmed]."

The evidence against vitamin C

On the other side of the coin, the journal Nature on April 9, 1998, published an article claiming that vitamin C increased free-radical damage to the adenine portion of DNA (and, incidentally, reduced free-radical damage to the guanine portion of DNA). I am told the investigators later published a retraction, but have not been able to locate it. Certainly, a 1998 study (Biochem J 1998;331:365) showed that the techniques used to isolate DNA from cells can oxidize adenine, so the oxidized adenine in the first study could have been damaged by the experimental technique, not the vitamin C.

Finally, among those people with the genetic tendancy to store excessive iron (called hemochromatosis), it is clear that the condition is made worse vitamin C because vitamin C enhances absorption of iron. We often recommend vitamin C to iron-deficient women to help them replace lost iron. So, it is important to monitor for excess iron and treat it before it results in heart disease, liver disease, arthritis and other problems. Our standard blood panel screens for hemochromatosis.

Summary

The great weight of the evidence is that vitamin C reduces the risk of cancer in humans.

3/28/04