With age comes increasing and sometimes cumulative exposure to both natural and synthetic environmental toxins, from heavy metals and pesticides to tobacco smoke and radiation--even life-giving oxygen can be harmful. Much of the damage from these exposures results from the generation of free radicals. These extremely reactive molecules or fragments of molecules have unpaired, or "free," electrons that in the normal course of metabolism are channeled into energy production. In some cells they may be used to kill viruses and bacteria. But because of their extremely high energy and inexorable search for another electron, they can also damage normal tissues if too many are produced or are not adequately controlled. The prematurely aged, wrinkled skin of smokers is caused by the free radical-induced damage that smoking engenders. In fact, smoking is probably the greatest source of voluntary exposure to free radicals.
Free radicals disrupt the normal production of DNA and RNA and alter the lipids, or fats, in cell membranes. They also damage cells lining blood vessels and interfere with the production of prostaglandins, which are derived from essential fatty acids and regulate many physiological functions. Partly as a result of free radical damage, aging leads to alteration of proteins (cross-linking). Proteins are complex chains of amino acids that bend into three-dimensional structures. Cross-linking takes place when attachments are formed along the chain in abnormal places, disrupting the protein's function. This leads to poor cell membrane performance in molecular transport, decreased enzyme activity, and inhibition of immune function.1 The total effect is a variable rate of decline depending on the level of exposure to free radicals.
Oxygen derivatives are involved in most free radical reactions. In a sense, the aging process could be viewed as one of gradual oxidation, or in physical chemistry terms--rusting. Although free radicals are usually associated with excessive oxygen and oxidation, in the right concentrations oxygen can reduce free radical damage.2 Oxygen free radicals include hydroxyl and superoxide, while activated oxygen species (those that react readily and trigger free radical production) include singlet oxygen and peroxide.