Antioxidants - the dark side
Per Lindahl1,*, Martin O. Bergo2, Volkan Sayin1
1Molecular and Clinical Medicine, 2Sahlgrenska Cancer Center, University of Gothenburg, Gothenburg, Sweden
Antioxidants are widely held to protect against cancer but clinical trials have reported inconsistent results; some studies even show adverse effects on lung cancer development. Our recent finding that antioxidants accelerate lung cancer progression in mice and the growth of human lung cancer cell lines, can explain those results.
Antioxidants are compounds that neutralize reactive oxygen species or ROS for short. ROS are byproducts of cellular metabolism that cause damage to DNA, proteins and other cellular components. Because DNA damage leads to cancer, dietary supplements containing high concentrations of antioxidants such as vitamins or minerals are held to protect against cancer, an idea that is fueled by the health industry.
We showed that mice with early lung cancers that were treated with dietary antioxidants developed larger and more advanced tumors compared to untreated controls, and died twice as fast. Similarly, antioxidants accelerated the growth of human lung cancer cell lines suggesting the results are clinically relevant. The most important defense mechanism against cancer is activation of the tumor suppressor p53. Our study revealed how antioxidant supplementation impairs this defense mechanism. By reducing the levels of ROS and DNA damage, antioxidants inactivate the p53-protein and help cancer cells to evade growth arrest or apoptosis.
Thus, antioxidant supplements could be dangerous for people at high risk for lung cancer, such as smokers or patients with chronic obstructive pulmonary disease (COPD), who may already have pre-cancerous lesions. Since COPD patients are treated with the antioxidant acetylcysteine to help break down mucus, there is an urgent need to determine whether this treatment increases the risk for lung cancer.