Vitamin C is often touted as a wonder - an antioxidant found in high amounts in citrus fruits, it is generally accepted as a cure-all for everything from the common cold to helping to fight off cancer.
Vitamin C supplements dominate sales of supplements in the US, accounting for more than $200 million in sales annually.
But are high doses of antioxidants actually good for us? New research making the headlines suggest that these antioxidants may actually contribute to the spread of cancer.
The study, published online in Science Translational Medicine is titled Antioxidants Accelerate Lung Cancer Progression in Mice (link to the primary article, which is, sadly, likely firewalled).
In this study, the researchers worked with mouse lung cancer models - genetically modified mice that can be induced to express a tumor-causing oncogene; several weeks after the researchers "turn on" this oncogene, the mice develop lung cancer. They then added either Vitamin E or NAC to the mice's food.
The results clearly demonstrated that addition of the antioxidants to these mice's diets led to a dramatic increase in cancer death. The mean survival time of the antioxidant mice is reduced to roughly 9 weeks from 22 weeks for mice not fed antioxidants. The mice additionally had more tumors, and the tumors were more aggressive.
The work goes on to provide the basis of a molecular mechanism for this observation. The antioxidants appear to do their job in the tumor cells very well; that is they reduce the amount of oxidative damage these cells experience. The low levels of oxidation experienced by these cells leads them to downregulate the genes the cells normally use to protect themselves from oxidative damage.
Somehow, and this is where there is a gap in the pathway these researchers have elucidated, the reduction in oxidative damage in these cells led to the down-regulation of one of the most important tumor supressor genes, p53. They suggest that it is likely this down-regulation of p53 that allows the tumors in these mice to progress so rapidly.
Finally, they demonstrate that supplying human lung cancer cells grown in tissue culture with antioxidants also leads to an increase in the growth of these cells.
Importantly, the antioxidants in this study increased the growth of tumors; the researchers can't draw conclusions on whether they might help prevent the initiation of tumors.
It is nearly impossible to extrapolate these results to human health; however, previous work in large clinical trials has suggested that Vitamin E and beta-carotene may promote tumor growth or formation in humans. The work discussed here may provide a molecular mechanism for this effect, and certainly suggest that anti-oxidants may not always have the effect that we want.