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Antioxidants have long been under the public eye for their alleged role in the prevention or treatment of cancer. Before we get to the details of how antioxidants might influence the effects of anticancer therapy, let us understand first the theoretical relationship between antioxidants and cancer.
Free radicals are chemical species with high reactivity that exist normally in our body. In fact, they are crucial for certain biological processes. However, like many things in life, an excessive amount of free radicals can be harmful, as it damages important components of cells. The damage caused to DNA is particularly worrying, as it may lead to the development of cancer.
Antioxidants, cancer development, and cancer prevention
Antioxidants are also naturally occurring chemicals, which aroused the interest of scientists because of their ability to combine with and neutralize free radicals. By exerting this action over free radicals, antioxidants preclude their damaging effects over cells. Antioxidants come from two sources: some are produced by our body (the endogenous antioxidants), but the great majority is obtained from our diet (the exogenous antioxidants).
Among the most relevant dietary antioxidants are beta-carotene and vitamins A, C and E.
The chemical relation between free radicals and antioxidants obviously sparked the question of whether antioxidants could have a role in preventing the cancerous consequences of free radical-induced cellular damages. Several large scale randomized controlled clinical trials, which constitute the hallmark of medical research because of their ability to provide reliable evidence, were then conducted worldwide. Overall, these trials were trying to find if antioxidant supplementation would in fact decrease the incidence or risk of certain types of cancer. After following thousands of patients over a large period of time, researchers came to the perhaps discouraging conclusion that dietary antioxidant supplements have no beneficial effect in primary cancer prevention.
Antioxidants and cancer treatment
But what about those who already have cancer? Could antioxidants be an important adjuvant to treatment, for instances?
However, evidence that antioxidants play any one of these roles is scarce and mixed.
In 2004, a group of researchers published in the Journal of Clinical Oncology a systematic review of the published clinical trials and observational studies investigating the effects of antioxidant supplementation in combination with conventional chemotherapy with or without radiation. It is important to note that systematic reviews are highly significant scientific tools, as they examine simultaneously all the information that exists about a given subject at a given point in time.
So, after accounting for all evidence, this team concluded that there is no proof that antioxidant supplements reduce the toxicity associated with anticancer therapy. This might be because the doses are inadequate, the potency is insufficient or these compounds simply do not exert such action. Timing of supplement intake might also be a factor to take into account. The authors suggest that supplementation might need to be introduced early in therapy, before the cumulative doses of chemotherapy and their associated adverse effects take over.