Free radicals are made in our bodies all the time and, if not destroyed, can lead to the development of cancer. By definition, free radicals are chemical substances that contain an odd number of electrons. Every atom has a nucleus and a certain number of electrons that orbit around the nucleus. This setup is very much like our solar system, with the sun in the middle and all the planets orbiting around the sun. The nucleus has a positive charge, and the electrons have a negative charge. The negative charges of electrons balance out the positive charge of the nucleus to give an overall charge of zero. Hence, the energy of a single atom is very stable at zero.
When high energy in any form (light, radiation, smog, tobacco, alcohol, polyunsaturated fats, etc.) hits an atom, an electron is kicked out of orbit. All of the energy that forced the electron out of orbit is transferred directly to the electron, making it highly energetic and unstable. Because it is so unstable, this electron quickly seeks another atom to reside in. This excited high-energy electron transfers very high energy to the new atom, which then becomes extremely unstable because of the newly acquired high energy. (An analogy to this state is a nine-month-old child who has a great deal of energy but is extremely unstable if left unattended.) This excited high-energy atom with its extra electron is called a free radical.
A free radical is unstable and must get rid of all the extra energy for the atom to become stable once again; hence the radical transfers its energy to nearby substances. (All these reactions take place within a fraction of a second.) When free radicals are made in the body, the high energy is transferred to body tissues, particularly to the polyunsaturated fats found in the cell membranes. The more unsaturated fats you eat, the more of them will be absorbed by the cell membranes and the higher the risk will be for membrane disruption by free radicals. If not counteracted, this process can lead to the development of cancer of the tissue affected by the radical.
FORMATION OF RADICALS
There are many processes in the body that initiate destructive radical reactions. Oxygen is crucial to us because it is required for all animal life. In certain instances, however, oxygen can be activated or split with high energy into very potent damaging radicals (superoxide) or a high-energy, unstable non-radical called singlet oxygen. Singlet oxygen has extremely high energy and is very unstable, and thus is very destructive to normal body tissues and cells.
Oxygen radicals can be both beneficial and harmful to us at different times under different circumstances. It is a beneficial reaction when a phagocyte kills an invading bacteria. This destruction is accomplished by oxygen radicals, which are made by the phagocyte when a foreign substance like a bacterium is ingested and taken inside the phagocyte. On the other hand, oxygen radicals can produce hydroperoxides, which are chemicals that form more radicals and damage cell membranes, thereby altering the cell's function. This can lead to the development of cancer. Singlet oxygen, a very-high-energy form of oxygen, has a shorter life than an oxygen radical but damages cells and tissues much more quickly. Not only does singlet oxygen have the potential of causing cancer by itself but it also activates carcinogens.
Another group of substances that encourage the formation of destructive free radicals is the polyunsaturated fatty acids. As you recall, saturated fats are to be avoided, and polyunsaturated fats are to be consumed only moderately. The reason for recommending minimal intake of polyunsaturated fats is that when oxygen or enzymes react with polyunsaturated fats to release their energy, a free radical is made. This free radical reacts with another polyunsaturated fat to produce a lot of hydroperoxide. The more unsaturated the fat is, the more hydroperoxides are made. And hydroperoxides produce more radicals, damage cell membranes, and can lead to the development of cancer.
Certain metal accumulations in the body can also initiate free radical formation by activating oxygen. Iron is one example of a metal that can form extremely potent hydroxyl radicals if found in excessive amounts in the body.
Ionizing radiation produces radicals and electrons that react to yield many different kinds of free radicals. Background radiation in the atmosphere at sea level probably does not produce free radicals in the body, however. Radicals produced in the body and by pollutants are much more important than those caused by radiation unless, of course, a person is receiving large doses of radiation for the treatment of a disease. At high levels of radiation, hydroperoxides are produced in addition to all the other free radicals.
It has been shown by R.E. Zelac et al. that the amount of ozone in smoggy air causes more tissue damage than does background radiation. Ozone reacts with almost every type of molecule in the body to form free radicals, which then damage cells. Ozone in normal amounts in the air can even form radicals with polyunsaturated fatty acids. One other component of smog, peroxyacetyl nitrate, can break down and produce singlet oxygen. Again, free radical scavengers or antioxidants will neutralize and inhibit ozone-induced radicals. These include vitamin E, vitamin C, selenium, and carotene.
Smog also contains nitrogen dioxides, which, like ozone, can form free radicals but to a lesser extent. These nitrogen oxides react with unsaturated fats of human cell membranes to form radicals that can damage the membranes. Antioxidants or radical scavengers like vitamin E can protect the membrane against radicals.
The components of smog, tobacco smoke, and other air pollutants can form radicals, especially in the lungs. Lung cancer is the leading cause of cancer deaths and is most common in the heavily industrialized areas of the country.
Alcohol and Carbon Tetrachloride
It is now known that excess alcohol and certain chloride-containing compounds (vinyl chloride, chloroprene, carbon tetrachloride) react with some enzymes (specifically microsomal mixed function oxidase system) in the liver to produce free radicals. These radicals can then locally damage liver cells and potentiate liver cancer or other deadly liver diseases.