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Excess Antioxidants May Increase Risk for Cancer and Diabetes

North Americans spend several million dollars each year on antioxidant pills even though they may increase risk for cancer and diabetes. One of the largest trials on antioxidants was halted because it showed that the antioxidant vitamin E offered no prevention of cancer and that it was associated with increased risk for prostate cancer (JAMA, October 12, 2011;306(14):1549-1556). Clinical trials also show that antioxidants do not prevent heart attacks or strokes (British Medical Journal, June 17, 2014).

The following discussion of antioxidants and oxidants is drawn from an article by James Watson that appeared in the March 19, 2013 issue of New Scientist. Watson won the Nobel Prize in 1962 for discovering the structure of the genetic material called DNA. He established the Human Genome Project and was director of the Cold Spring Harbor Laboratory in New York, focusing on the study of cancer.

Oxidants, Not Antioxidants, Help to Prevent Cancer
The chemical reactions in your body that turn food into energy release huge amounts of chemicals called oxidants that can damage the cells in your body. To protect you, your cells are supposed to produce chemicals called antioxidants that neutralize the oxidants. However, if your body produces too many antioxidants, they can destroy the genetic material called DNA and proteins in cells to cause cancer (Open Biology, published online January 9, 2013). Research has shown that vegetables such as Brussels sprouts and broccoli protect a person from developing cancer by increasing production of oxidants (JAMA, February 28, 2007;297(8).

Doctors treat cancers with ionizing radiation that kills cancer cells by generating oxidants. Chemotherapy drugs, such as paclitaxel, kill cancer cells by generating very powerful oxidants: superoxide, hydrogen and hydrogen peroxide (Cancer Res, September 15, 2005;65(8455)).

How Antioxidants Promote Cancer
Pancreatic cancer has no effective treatment, and most people with this cancer die in fewer than five years. Pancreatic cancer cells produce large amounts of antioxidants that prevent oxidants from killing the cancer cells, so pancreatic cancer is almost always fatal. Several research papers show that antioxidants block apoptosis (programmed cell death) to keep cancer cells alive so that they can invade other tissues in the body and kill the patient. Every cell in your body lives only so long and then dies. This is normal and called apoptosis. However cancer means that the cells lose apoptosis and forget to die. They multiply so fast that they accumulate in the body and invade other tissues. For example, pancreatic cancer never kills anyone as long as the pancreatic cancer cells are only in the pancreas. When pancreatic cancer cells invade other organs such as the liver, stomach, intestines and other tissues in the belly, and even the lungs and brain, they destroy the invaded tissues and kill the patient.

Drugs That Block Antioxidants May Cure Some Cancers
Since we now know that antioxidants protect cancer cells from chemotherapy, we may be able to treat some cancers with drugs that block antioxidants. Kevin Struhl at Harvard Medical School screened more than 1000 drugs to see which drugs kill cancer cells (Cancer Res, Oct 1, 2009;69(19):7507-11). He found that metformin (Glucophage), used to treat diabetes, reduces antioxidants and increases oxidants to reduce the incidence of cancer of the pancreas, lung and colon by 20 to 40 per cent. It is widely prescribed and appears to be safe (Gastroenterology, August 2009;137(2):482–488).

Excess Antioxidants May Lead to Diabetes
In Type 2 diabetes, antioxidants block oxidants from lowering high blood sugar levels and telling the liver to respond to insulin to drive high blood levels of sugar from the bloodstream into the liver (Proceedings of the National Academy of Sciences, published online May 11, 2009) So diabetes appears to be caused, at least in part, by antioxidants in the liver.

Exercise helps to prevent type 2 diabetes by increasing production of oxidants by the mitochondria in muscle cells. However, when a person takes antioxidants, such as vitamin C and E pills, exercise does not prevent diabetes because the antioxidants neutralize the oxidants produced by the mitochondria (The Journal of Physiology, July 22, 2013). Another study showed that exercise helps to prevent colon cancer by causing mitochondria to generate large amounts of oxidants (Am J Epidemiol, 2003 Aug 1;158(3):214-24).

My Recommendation
No good data show that heart attacks, cancers or diabetes are prevented by taking antioxidant pills such a vitamins A, C, and E, the mineral selenium or other fancy-named antioxidant pills. Some data show that antioxidant pills may increase risk for cancer and reduce benefits of chemotherapy. Instead of taking pills, eat a varied diet that contains plenty of plants.

Checked 6/24/15

June 22nd, 2014
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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