Free radicals are highly reactive molecules that are produced in the body naturally as a byproduct of metabolism (oxidation), and by exposure to toxins in the environment such as tobacco smoke and ultraviolet light.
Free radicals contain an unpaired electron. Simply put, they are in a constant search to bound with another electron to stabilize themselves-- a process that can cause damage to DNA and other parts of human cells. This damage may play a role in the development of cancer and other diseases, and accelerate the aging process.
It is thought that antioxidants, such as vitamin C, vitamin E and beta-carotene, may reduce the damage caused by free radicals in our bodies by inhibiting their formation.
While dietary sources of antioxidants have been correlated with a lower risk of developing the lung cancer, it is important to note that taking supplements of some of these (such as beta-carotene and vitamin E) may actually increase risk.
For those who are going through treatment for cancer, it is very important to discuss any antioxidant supplements -- or any supplements, for that matter -- with your oncologist. Some treatments for cancer, such as radiation, create free radicals in an effort to kill cancer cells. In this setting, the use of antioxidants could in theory decrease the effectiveness of treatment.