A new study calls into question one of the most widely accepted beliefs about cancer prevention: Eating foods that are rich in antioxidants can help decrease cancer risk. Not necessarily, say researchers at the University of Gothenburg Sahlgrenska Cancer Center in Sweden. Antioxidants may actually increase lung cancer risk for smokers and people with chronic obstructive pulmonary disease (COPD).

Antioxidants are supposed to protect the body from cancer by preventing free radicals from damaging cells. “These radicals can damage almost anything inside the cell, including DNA, and DNA damage can lead to cancer,” explained study leader Dr. Martin Bergo. By neutralizing free radicals, antioxidants should decrease the possibility of DNA damage and cancer risk.

However, Swedish researchers found that in people with cancerous or precancerous cells, the body’s response to antioxidants appears to backfire. Instead protecting, antioxidants short-circuit a key immune response to cancerous cells, accelerating cancer progression, according to a HealthDay report posted on WebMD.

The study tested response to vitamin E and acetylcysteine, an antioxidant supplement, in mice with early lung cancer. “We found that antioxidants caused a threefold increase in the number of tumors and caused tumors to become more aggressive,” Dr. Bergo said. “Antioxidants caused the mice to die twice as fast, and the effect was dose-dependent.”

The findings are of concern not only because they fly in the face of current cancer prevention recommendations, but also because acetylcysteine is commonly used to improve breathing in COPD patients. Until further testing can be done, researchers recommend that people at risk of lung cancer avoid taking antioxidant supplements. Issels cancer experts point out that study findings were limited to lung cancer and that antioxidants received through food were not implicated.