July 10, 2014
Scientists Question Antioxidant Supplements’ Effect on Cancer
Featuring: Sharon Zarabi, RD, Nutritionist, Lenox Hill Hospital
Dietary supplements rich in antioxidants may do more harm than good when it comes to cancer prevention, a Cold Spring Harbor Laboratory scientist and a Chicago colleague suggest in a newly published report.
Dr. David Tuveson and Navdeep Chandel of Northwestern University's Feinberg School of Medicine, in a contrarian hypothesis certain to stoke controversy, wrote in Thursday's New England Journal of Medicine that dietary antioxidants "have consistently failed to reduce the incidence of carcinoma." They referred to conclusions drawn in numerous clinical trials.
Tuveson, an expert in pancreatic cancer, directs the Lustgarten Foundation's pancreatic research lab at Cold Spring Harbor Laboratory and heads research for the Lustgarten Foundation in Bethpage. Chandel, of Northwestern, specializes in the study of oxidative damage to cells. Both are widely known for their expertise in the fight against cancer. The scientists primarily examined the effects of antioxidants in the form of dietary supplements and studied how well the nutrients taken in pill form reduced the risk or presence of cancer.
Many studies over the years have shown that antioxidants taken by participants in major clinical trials that focused on cancer prevention did not thwart the disease. In some cases, antioxidants accelerated cancer development. Participants in these trials took dietary supplements. Foods were not studied.
Antioxidants include well-known nutrients -- vitamins A, C and E, as well as the mineral selenium. All are inhibitors of damaging forms of reactive oxygen in the body's tissues.
Reactive oxygen molecules include peroxide, which is produced in small amounts by certain healthy cells, particularly white cells involved in destroying invasive microbes. Reactive oxygen also increases when unhealthy fats, such as trans fats, are consumed.
Some of these reactive forms of oxygen are commonly known as free radicals, which are capable of destroying human tissue and, theoretically, promoting cancer development. Antioxidants are believed to stop reactive oxygen in its tracks.
But antioxidants may fail to show a beneficial effect against cancer, the two doctors reported, because these nutrients do not act in the mitochondria -- critical sites in cells where rogue tumor-promoting forms of oxygen are produced.
Nutritionist Mindy Haar, director of the Department of Interdisciplinary Health Sciences at New York Institute of Technology in Old Westbury, said while Tuveson and Chandel have proposed a provocative hypothesis, she still recommends consumption of foods rich in antioxidants.
"This is an interesting paper, but I still think it's a good idea to base your diet on a variety of fruits and vegetables," she said, underscoring the importance of dark, leafy greens and other whole foods rich in antioxidants.
Haar, who has written extensively on nutrition, said she has been criticized for failing to promote the consumption of dietary supplements. But, she noted, supplements do not have the same properties as foods. "Foods contain a variety of phytonutrients," she said, referring to plant-based compounds that can prevent the development of a wide range of disorders, not only cancer.
Sharon Zarabi, a nutritionist at Lenox Hill Hospital in Manhattan, said there is a synergistic effect between nutrients in foods. Supplements do not have the same composition.
"I think that it's difficult to test supplements compared to foods that are whole," Zarabi said. "All vitamins and minerals act together in foods to prevent free radicals."
However, Zarabi noted that antioxidants are complex compounds with the capacity to transform themselves inside cells -- sometimes changing into free radicals.