Media Overlooks Human Studies on Vitamin C

Media Overlooks Human Studies on Vitamin C

This section is compiled by Frank M. Painter, D.C.
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Thanks to the Nutrition Science News for this article!

by Bill Sardi

Researchers at the University of Pennsylvania Center for Cancer Pharmacology and the news media overlooked five current human studies that disprove the notion that high-dose vitamin C causes DNA damage. Instead, the media exploited one test-tube study, published in the June 15 issue of Science, whose researchers concluded that the daily equivalent of 200 mg vitamin C could potentially cause cancer.

Test-tube studies usually precede animal or human studies, and laboratory test results often do not match living systems. In this case, human studies do not confirm that vitamin C is toxic to living cells or DNA.

Even though researchers are uncertain why vitamin C supplements do not always reduce cancer risk, no studies confirm that vitamin C supplement users are at greater risk for cancer. One such report with curious results, the Second National Health and Nutrition Examination Survey (NHANES II), studied 8,453 Americans who were 30 years old at baseline. High serum ascorbic acid levels were protective against cancer death in men, but were unexpectedly associated with an increased cancer death risk in women. [1]

However, other studies do not confirm such an association, particularly supplementation studies. For example, a recent study conducted among 711,891 men and women in the U.S. revealed the use of vitamin C supplements was associated with more than a 50 percent drop in relative risk for colorectal cancer mortality. [2] Another survey taken among 1,363 males found that vitamin C supplements were associated with a reduced risk of prostate cancer. [3]


The Science test-tube study was submitted in early February and approved for publication in May 2001. Although the article cited published references dated as late as 2000, it omitted four of the five human studies that do not confirm that vitamin C causes DNA damage, all of which were published in 2000.

For example, researchers at Johns Hopkins University did not find evidence of a "significant main effect or interaction effect on oxidative DNA damage in non-smoking adults" with 500 mg/day vitamin C supplementation. [4]

In a German study, researchers found that 1,000 mg/day vitamin C consumed by smokers and non-smokers alike for seven days did not produce DNA damage as measured by the number of micronuclei in blood lymphocytes. [5]

In another study, conducted by Immunosciences Laboratory in California, 20 healthy volunteers were divided into four groups and given either placebo or daily doses of 500, 1,000, or 5,000 mg ascorbic acid for two weeks. Researchers concluded that "ascorbic acid is an antioxidant and that doses up to 5,000 mg neither induce mutagenic lesions nor have negative effects on natural killer cell activity, apoptosis, or cell cycle." [6]

In London, researchers measured the effects of 260 mg/day vitamin C and vitamin C plus iron in humans and concluded that there was "no compelling evidence for a pro-oxidant effect of ascorbate supplementation, in the presence or absence of iron, on DNA base damage." [7]

In Ireland, researchers gave 1,000 mg vitamin C to volunteers for 42 days and concluded that "supplementation with vitamin C decreased significantly hydrogen peroxide-induced DNA damage in peripheral blood lymphocytes." [8]


The news media did not investigate whether there was contrary data on this topic, nor did they interview other scientific sources, such as the Linus Pauling Institute, the Vitamin C Foundation, or the Council for Responsible Nutrition. A cub reporter could have uncovered the contrary human studies in a 30-minute Medline search.

Researchers have recently been exploring vitamin C's dual nature. Is vitamin C a pro-oxidant rusting agent, or is it an antioxidant cellular preservative? In 1998, Nature published a report similar to the University of Pennsylvania study.

Researchers then claimed that high-dose vitamin C had "rusting" properties in living cells and that 500 mg vitamin C daily oxidizes adenine, one of DNA's four components. But the researchers overlooked the fact that high-dose vitamin C also increases the level of guanine, another one of DNA's nucleic acids. The researchers failed to point out their paradoxical results and the news media made inaccurate headlines out of the story then, as they are doing now—that high-dose vitamin C is potentially dangerous.

One more thought about vitamin C: Most animals make their own vitamin C from an enzyme missing in humans and some primates. The concentration of vitamin C in animals is about what the researchers at the University of Pennsylvania allege would cause DNA breaks and promote cancer. However, this is clearly not observed in animals, and it makes the case again that what may be true in an isolated test tube does not always correlate to results found in living systems.

Bill Sardi is a health journalist in Diamond Bar, Calif., is author of The Iron Time Bomb (Bill Sardi, 1999).


1. Simon, JA, et al.
Relation of serum ascorbic acid to mortality among US adults.
J Am Coll Nutr 2001 June;   20 (3):   255-63

2. Jacobs EJ, et al.
Vitamin C and vitmain E supplement use and colorectal cancer mortality in a large American Cancer Society cohort.
Can Epid Biomarker Prev 2001;   10:   17-23

3. Kristal AR, et al.
Vitamin and mineral supplement use is associated with reduced risk of prostate cancer.
Can Epid Biomarker Prev 1999;   8:   887-92

4. Huang HY, et al.
The effects of vitamin C and vitamin E on oxidative DNA damage: results from a randomized controlled trial.
Cancer Epidemiol Biomarkers Prev. 2000 Jul;   9 (7):   647-52

5. Schneider M, et al.
Protective effects of vitamins C and E on the number of micronuclei in lymphocytes in smokers and their role in ascorbate free radical formation in plasma.
Free Radic Res 2001 Mar;   34 (3):   209-19

6. Vojdani A, et al.
New evidence for antioxidant properties of vitamin C.
Cancer Detect Prev 2000;   24 (6):   508-23

7. Proteggente AR, et al.
Potential problems of ascorbate and iron supplementation: pro-oxidant effect in vivo?
Biochem Biophys Res Commun 2000 Nov 2;   277 (3):   535-40

8. Brennan LA, et al.
The effect of vitamin C or vitamin E supplementation on basal and H2O2-induced DNA damage in human lymphocytes.
Br J Nutr 2000 Aug;   84 (2):   195-202

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