Highly reactive chemicals that often contain oxygen and are produced when molecules are split to give products that have unpaired electrons. This process is called oxidation.
Free radicals can damage important cellular molecules such as DNA or lipids or other parts of the cell. They are constantly attacking body proteins, carbohydrates, fats and DNA, causing potentially serious damage unless checked.
How Are Oxygen Free Radicals Produced in the Body?
Free radicals can originate in body cells in various ways. External radiation, including ultraviolet light, X-rays and gamma rays from radioactive material, is a potent source. Such radiation acts by breaking linkages between atoms, leaving the radicals with their unpaired electrons to wreak their damage. Free radicals occur in the course of various disease processes. In a heart attack, for instance, when the supply of oxygen and glucose to the heart muscle is cut off, the real damage to the muscle is caused by the vast numbers of free radicals that are produced.
Chemical poisoning of many kinds promotes free radicals, as does excessive oxygen intake from inhaling pure oxygen. The body's necessity to break down a wide range of drugs to safer substances (detoxification) also involves free radical production. The poisonousness (toxicity) of many chemicals and drugs is actually due either to their conversion to free radicals or to their effect in forming free radicals.
Inflammation—one of the commonest kinds of bodily disorder—is associated with free radical production, but the free radicals are probably the cause of the inflammation rather than the effect. However, the body actually uses free radicals to kill bacteria within the scavenging cells of the immune system—the phagocytes—and when excessive numbers of these are present in an inflamed area the free radical load almost certainly adds to the tissue damage, making everything worse. This is probably what happens in rheumatoid arthritis, for instance.
Three Magical Enzymes
The breakthrough that caused medical scientists really to begin to look seriously at free radicals was the astonishing discovery that the body actually produces large quantities of a substance (an enzyme) whose only function is to break down the dangerous superoxide free radical. This enzyme is SuperOxide Dismutase (commonly called SOD by the scientists). There is no reason to be rude about this marvelous enzyme, for we really need it. This enzyme converts dangerous superoxide free radicals to the less dangerous hydrogen peroxide. This is still fairly powerful stuff, capable of turning us all blonde, and is quite damaging to tissues. Happily, the body produces another enzyme, called Catalase, which immediately breaks down the hydrogen peroxide to water and oxygen, and all is well. There is a third natural antioxidant enzyme called, Glutathione peroxidase which also reduces hydrogen peroxide to water.
Each of these enzymes is made in cells under the instructions of a length of genetic code in DNA. Every cell in our bodies contains the instructions for making these three enzymes.