July 11, 2014
Foods Rich In Antioxidants May Promote Cancer Growth
Rebekah Eliason for redOrbit.com – Your Universe Online
Around the globe, health conscious people have sought out antioxidant supplements and eaten diets rich in antioxidants for decades in an attempt to live healthy lives for a long time. Surprisingly, recent clinical trials have dashed the hopes of people taking antioxidant supplements to reduce the risk of cancer.
In almost all antioxidant trials, there have been no protective effects against cancer. Among several of the trials, researchers found a link between the supplements and an increased risk of certain types of cancer. One specific trial found that smokers who take extra beta-carotene increased their risk of lung cancer instead of lowering the risk.
The authors proposed in a brief paper why antioxidant supplements might not reduce the development of cancer and why they actually seem to be harmful.
The team’s discoveries are based on recent information about the understanding of the system in our cells that works to naturally balance between oxidizing and anti-oxidizing compounds. These chemical compounds are involved in a reaction known as redox, which are essential to cellular chemistry.
Within cells, essential oxidants such as hydrogen peroxide are manufactured. It is understood that in large quantities oxidants are toxic, but cells naturally create their own antioxidants to neutralize them and keep the balance. Many people decided to give the body a boost in this process by taking lots of antioxidants to counter the toxic effects of hydrogen peroxide and other "reactive oxygen species," or ROS, as they are called by scientists. Since cancer cells are known to generate higher ROS levels to feed their growth, people were all the more anxious to help the body neutralize the toxic species.
Study leaders David Tuveson, MD, PhD, Cold Spring Harbor Laboratory Professor and Director of Research for the Lustgarten Foundation, and Navdeep S. Chandel, PhD, suggest that taking pills or eating antioxidant foods are ineffective because they do not reach the critical site in cells where the tumor-promoting ROS are produced. Instead, supplements and dietary antioxidants will accumulate in other areas of the cell, “leaving tumor-promoting ROS relatively unperturbed," the researchers say.
In cancer cells, quantities of both ROS and natural antioxidants are higher. Higher levels of antioxidants are a natural defense by cancer cells to keep high oxidant levels in check to enable continued growth. In fact, say Tuveson and Chandel, therapies that raise the levels of oxidants in cells may be beneficial, whereas those that act as antioxidants may further stimulate the cancer cells. Radiating actually kills cancer cells by dramatically raising oxidant levels. Chemotherapeutic drugs actually work the same way by killing tumor cells from oxidation.
The authors then suggest in an interesting paradox that, "genetic or pharmacologic inhibition of antioxidant proteins,” which is a concept that has been successfully tested in models of rodent lung and pancreatic cancers, might be a helpful therapeutic approach in humans. The authors say the key is to identify the antioxidant proteins and pathways used only by cancer cells and not healthy cells. If antioxidant production is impeded in healthy cells, the delicate redox balance of normal cellular function will be destroyed.
In further research, the authors propose to profile antioxidant pathways in tumor and adjacent normal cells in hopes of identifying possible therapeutic targets.
This study was published July 10, 2014 in The New England Journal of Medicine.