CORVALLIS, Ore. - A study just published in the journal Nature which suggests moderate vitamin C supplementation may actually be harmful should be viewed against the larger body of research which has generally come to quite the opposite conclusion, says one expert at Oregon State University.
This new research, which was done by scientists at the University of Leicester in the United Kingdom, found evidence that daily 500 milligram supplements of vitamin C might actually increase DNA damage and potentially the risk of cancer, as gauged by one biological "marker" of such cellular damage.
But Balz Frei, a professor and director of the Linus Pauling Institute at OSU, says the new finding is contrary to many others, directly contradicts at least one other recent study, and focuses too narrowly on a single biological "marker" that has yet to be proven as a good indicator of oxidative stress and cellular damage.
"The findings of this new study should not be overemphasized," said Frei, who is one of the world's leaders in the study of vitamins and other micronutrients in disease prevention and therapy.
"Looking at a single biological marker of oxidative stress, the researchers made conclusions that may not have an adequate scientific basis," Frei said. "The value of vitamin C in lowering the risk of cancer, heart disease and other serious health problems must be considered in its totality, not just in a focus on one single aspect of its biological effect."
Based on the larger body of research done on vitamin C, including his own, Frei said that he still believes a 200 milligram supplement of the vitamin each day would be appropriate for any healthy person. Larger levels could have value for people with actual disease problems, and "I have little or no doubt that any level of supplementation up to one full gram per day would not be harmful," he said.
In the study done in the United Kingdom, scientists looked at two biological markers of oxidative DNA damage - 8-oxoguanine and 8-oxoadenine. According to the study, both are indicators of cellular damage being done in the human body, and higher levels of either compound would be considered bad.
Their research found that with supplementation of vitamin C the levels of one marker decreased - which is good and what one might expect from an antioxidant vitamin - but levels of the other supposed indicator of cell damage rose.
According to Frei, there are several problems with the scientific conclusions of the study. They include:
- The biological marker of DNA damage which increased, 8-oxoadenine, has not been clearly established as a marker of damaging oxidative stress nearly so much as the other marker studied;
- One fact established by other research is that the other marker which decreased, 8-oxoguanine, has 10 times or more the mutagenic potential as 8-oxoadenine; the two "markers" may not be equal in their potential to indicate cellular damage, increase the chance of a mutation and thus, cancer;
- Research announced recently at a professional conference in California, but not yet published, directly contradicts the finding that 8-oxoadenine levels increase with vitamin C supplementation.
"Frankly, I question whether these data and the findings of this new study will hold up as we analyze this further," Frei said. "And even if it's true that the level of this one biological marker, which supposedly shows cellular damage, is increasing with vitamin C supplementation, you have to view that in a larger context."
Dietary supplementation with anti-oxidants such as vitamin C clearly have a wide range of biological effects, Frei said, and numerous studies over a period of years have shown the overall impact of them to be favorable for some of the most serious disease problems in the world, including cancer.
"You can't look at a single suggestion of an increase in a single oxidative DNA damage product and conclude that vitamin C supplementation is a bad thing," Frei said. "One has to consider the totality of scientific evidence based on measurements of many different DNA damage products and damage to other important biological targets relevant to human disease."
"Our own research, for instance, is now looking at the impact of vitamin C on damage to lipids, which is an important factor related to heart disease. And it appears to be showing supplementation can be of significant value.
"You have to look at the big picture, not one little part or one single study," he said.