- What are free radicals and do they have any role in the formation of cancer?
- What are antioxidants?
- Can antioxidant supplements help prevent cancer?
- Should people who have already been diagnosed with cancer take antioxidant supplements?
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What are free radicals and do they have any role in the formation of cancer?
Free radicals are highly reactive chemical compounds that can damage cells. They are created when an atom or molecule (a chemical compound that has two or more atoms) gains or loses an electron (a small, negatively charged particle found in atoms). Free radicals are naturally formed in the body and play an important role in many normal cell processes ( 1 , 2 ). However, in high concentrations, free radicals can be dangerous to the body and can damage all the major components of cells, including DNA, proteins and cell membranes. Damage to cells caused by free radicals, especially DNA damage, may play a role in the formation of cancer and other health conditions ( 1 , 2 ).
Abnormally high concentrations of free radicals in the body can be caused by exposure to ionizing radiation and other toxins from the environment. When ionizing radiation hits an atom or a molecule in a cell, an electron can be lost, resulting in the formation of a free radical. The production of abnormally high concentrations of free radicals is the mechanism by which ionizing radiation destroys cells. In addition, some environmental toxins, such as cigarette smoke, some metals and atmospheres with high oxygen concentration, may contain large amounts of free radicals or may stimulate body cells to produce more free radicals.
Free radicals that contain the oxygen element are the most common type of free radicals produced in living tissues. They are also called " reactive oxygen species ", or "ROS" ( 1 , 2 ).
What are antioxidants?
Antioxidants are chemical compounds that interact with free radicals and neutralize them, preventing them from causing harm. Antioxidants are also known as "free radical scavengers".
The body produces some of the antioxidants it uses to neutralize free radicals. These antioxidants are called endogenous antioxidants. However, the body depends on external (exogenous) sources, the diet mainly, to obtain the rest of the antioxidants it needs. These exogenous antioxidants are commonly called food antioxidants. Fruits, vegetables and cereals are rich sources of food antioxidants. Some food antioxidants are also available as a dietary supplement ( 1 , 3 ).
Examples of food antioxidants are beta-carotene , lycopene and vitamins A, C and E ( alpha-tocopherol ). It is often thought that the mineral element selenium is a food antioxidant, but the antioxidant effects of selenium are most likely due to the antioxidant activity of proteins in which selenium is an essential compound (ie, proteins containing selenium) and not of the selenium itself ( 4 ).
Can antioxidant supplements help prevent cancer?
In animal studies and laboratory studies, it has been indicated that the presence of higher concentrations of exogenous antioxidants prevents the type of free radical damage that has been associated with the presence of cancer. For this reason, researchers have studied whether the use of food antioxidant supplements can help lower the risk of suffering or dying from cancer in humans.
Many observational studies , including case-control studies and cohort studies have been carried out to investigate whether the use of dietary antioxidant supplements is associated with lower risks of cancer in humans. In general, these studies have offered mixed results ( 5 ). Since observational studies can not adequately control for biases that may influence the results of the studies, it is necessary to look with caution at the results of any individual observational study.
Randomized controlled trials, however, do not have most of the biases that limit the reliability of observational studies. For this reason, randomized studies are considered to provide the strongest and most reliable verification of the benefit and harms of a health-related intervention. To date, nine randomized controlled studies of dietary antioxidant supplements for cancer prevention have been carried out in the world. Many of the studies were sponsored by the National Cancer Institute. The results of these nine studies are summarized below.