About 50% of the American public loads up on nutritional supplements, including those containing high doses of antioxidants – especially vitamin A (or beta-carotene, which is known as “pro-vitamin A”), vitamin C and vitamin E. These antioxidants fight notorious free radicals that are capable of damaging proteins, cell membranes, and our DNA, potentially leading to inflammation and an increased risk of cancer and many chronic diseases.
But there has been a recent scare in the antioxidant world – with headlines reading “Antioxidants CAUSE Cancer!” After decades of research examining the potential benefits of consuming antioxidants, what brings about this scary news story? Especially when we all thought that loading up on antioxidant foods and supplements was a good thing?
Here’s the scoop. To date there have been nine clinical trials worldwide on antioxidant supplementation and cancer prevention and the results have been surprisingly mixed. In most cases, supplementation had no impact on the risk for a variety of cancers. However, in some studies antioxidant supplementation actually increased cancer risk. The most notable of these studies were the CARET trial and the ATBC Study in which daily supplementation with beta-carotene or a combination of beta-carotene and vitamin A increased lung cancer incidence and all-cause mortality in smokers. There was also the SELECT Trial in which daily vitamin E supplementation increased prostate cancer in older men. We have known about these trial results for a while now, but why all the attention on the negative impact of antioxidants on cancer now?
In a compelling study released in January, researchers bred mice to be prone to lung cancer and treated them with either vitamin E or another antioxidant called N-acetyl-cysteine. Surprisingly, animals given either antioxidant had much more aggressive tumor development and more likely to die from the cancer. Upon closer examination, it appeared that the antioxidants actually inhibited the activity of a gene called p53 – whose job it is to destroy cancer cells! So what this study suggests, is that in high doses, antioxidants may actually help protect the cancer cells by turning off the p53 cancer sweeper, which then enables the cancer to continue to grow.