The study, which was just published in a professional journal, Proceedings of the National Academy of Sciences, also contradicts the conclusions of some research that was widely publicized three years ago. It had suggested that this essential nutrient might actually have toxic effects.
The new OSU study confirmed the results of that earlier laboratory study, which had found vitamin C to be involved in the formation of compounds potentially damaging to DNA.
But that research, the scientists say, only provided part of the story about what actually happens in the human body. The newest findings explain for the first time how vitamin C can react with and neutralize the toxic byproducts of human fat metabolism.
"This is a previously unrecognized function for vitamin C in the human body," said Fred Stevens, an assistant professor in the Linus Pauling Institute. "We knew that vitamin C is an antioxidant that can help neutralize free radicals. But the new discovery indicates it has a complex protective role against toxic compounds formed from oxidized lipids, preventing the genetic damage or inflammation they can cause."
Some earlier studies done in another laboratory had exposed oxidized lipids – which essentially are rancid fats – to vitamin C, and found some reaction products that can cause DNA damage. These test tube studies suggested that vitamin C could actually form "genotoxins" which damage genes and DNA, the types of biological mutations that can precede cancer.
But that study, while valid, does not tell the whole story, the OSU researchers say.
"It's true that vitamin C does react with oxidized lipids to form potential genotoxins," said Balz Frei, professor and director of the Linus Pauling Institute, and co-author on this study. "But the process does not stop there. We found in human studies that the remaining vitamin C in the body continues to react with these toxins to form conjugates - different types of molecules with a covalent bond - that appear to be harmless."
In human tests, the OSU scientists found in blood plasma extraordinarily high levels of these conjugates, which show this protective effect of vitamin C against toxic lipids.
"Prior to this, we never knew what indicators to look for that would demonstrate the protective role of vitamin C against oxidized lipids," Stevens said. "Now that we see them, it becomes very clear how vitamin C can provide a protective role against these oxidized lipids and the toxins derived from them. And this isn't just test tube chemistry, this is the way our bodies work.
"This discovery of a new class of lipid metabolites could be very important in our understanding of this vitamin and the metabolic role it plays," Stevens said. "This appears to be a major pathway by which the body can get rid of the toxic byproducts of fat metabolism, and it clearly could relate to cancer prevention."
Oxidation of lipids has been the focus of considerable research in recent years, the scientists say, not just for the role it may play in cancer but also in other chronic diseases such as heart disease, Alzheimer's disease, and autoimmune disorders.
The toxic products produced by fat oxidation may not only be relevant to genetic damage and cancer, researchers believe, but are also very reactive compounds that damage proteins. For instance, there's a protein in LDL, the "bad" cholesterol in your blood, which if damaged by toxic lipids can increase the chance of atherosclerotic lesions.
In continuing research, the OSU team plans to study the role of this newly understood reaction between vitamin C and toxic lipids in atherosclerosis. In clinical studies they plan to examine the blood chemistry of patients who have been diagnosed with coronary artery disease, compared to a healthy control group.
"In the early stages of atherosclerosis, it appears that some of these toxic lipids make white blood cells stick to the arterial wall, and start an inflammatory process that ultimately can lead to heart disease or stroke," Frei said. "When we better understand that process and the role that micronutrients such as vitamin C play in it, there may be strategies we can suggest to prevent this from happening."
The new findings, the OSU scientists say, also points to new biomarkers that can be useful in identifying oxidative stress in the human body. They may provide an indicator of people who may be at special risk of chronic disease.
By David Stauth, 541-737-0787
SOURCE: Fred Stevens, 541-737-9534
Balz Frei, 541-737-5078
Journal
Proceedings of the National Academy of Sciences