One fascinating thing about science is that you are sometimes confronted with surprises—data that don't fit earlier thinking or that even appear to contradict what you think you already know. Consider, for example, these recent findings about radiation and pollution:
• The average lifespans of rats were increased when they were continually exposed to levels of radiation about three times normal background. (At higher levels, average lifespans are decreased.)
• There was no detectable increase in genetic defects or cancer levels in multigeneration studies of rats exposed to radiation at levels about three times normal background.
• In one region of China (as recently reported in Science), the population lives at a level of natural background radiation three times that of populations in surrounding areas. No significant difference in cancer rates or birth defects has been found in this large-scale study.
• Which city do you think has the highest cancer rate? Birmingham, Alabama; Pittsburgh, Pennsylvania; Newark, New Jersey; Los Angeles, California; or San Francisco, California? Curiously, the city with the lowest level of air pollution by far—San Francisco—has the highest cancer incidence, adjusted for the population's age distribution. Newark, New Jersey, which 20 miles downwind still smells like an oil refinery, has the same incidence of cancer as the United States as a whole.
These are data that do not fit the popular media theories of radiation and pollution effects—namely, that every level of radiation is unsafe and causes cancer and that we have to control air pollution because it causes cancer. But these seemingly confusing results do fit into an emerging understanding of the interaction between living organisms and radiation and other pollutants.
Damage from ionizing radiation such as x-rays is an example of a free-radical disease. Radiation kills by creating free radicals—molecules or atoms with an unpaired electron, which are extremely chemically reactive and dangerous. These free radicals are mutagens (cause mutations) and carcinogens (cause cancer) when they damage DNA. They attack fats in the body, causing them to become peroxidized (rancid) fat. Besides being mutagens, carcinogens, atherogens (atherosclerosis-causing), thrombogens (clot-promoting), and immune suppressants, peroxidized fats can break down to form more free radicals, causing a chain reaction of further damage.
But external radiation is not usually an important source of free-radical damage to organisms. Free-radical reactions are a necessary part of normal metabolism. For example, the manufacture of ATP (the universal energy storage molecule) requires free-radical reactions. Thus, free radicals are constantly created in the body and, as suggested by Dr. Denham Harman (the originator of the free-radical theory of aging), can be considered internal radiation. In fact, all air-breathing organisms on this planet have elaborate defense and control systems for free radicals.
The body's free-radical control systems are not perfect, however, and damage occurs throughout life. Free radicals are now considered by scientists studying them to be major causative factors in aging, cardiovascular disease, cancer, arthritis, immune-system incompetence, and other less serious conditions including bruises and even dandruff. Our sophisticated free-radical control system includes special antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase, catalase, compounds such as reduced glutathione, and antioxidant nutrients such as vitamins A, C, E, B-1, B-3, B-5, B-6, PABA, the amino acid cysteine, and the minerals zinc and selenium.
One important feature of the antioxidant enzymes is that they are substrate-inducible. That means that when there are more free radicals in your body, these enzymes are manufactured in greater quantities. Thus, when radiation levels are increased (up to the limit of inducibility), more protective enzymes are produced. The maximum lifespan of individuals of several mammalian species is directly proportional to their concentrations of SOD and glutathione peroxidase divided by the level of metabolic free-radical-generating activity. The research findings mentioned above probably reflect a lifespan-increasing effect of that increase in the levels of protective enzymes. In other words, zero radiation may not be optimal from the point of view of longevity.
The principal eye irritants in the type of photochemical smog found in Los Angeles are organic peroxides called PAN (peroxyacetylnitrile and peroxyacetylnitrate). Again, the increase in pollutants increases production of protective enzymes. You've probably noticed that when you are first exposed to a heavy smog, your eyes burn and your lungs feel uncomfortable. But after you've been in heavy smog for a few days or so, the smog no longer produces these physical symptoms. This is not a result of your "getting used" to the smog or becoming insensitive to the discomfort. It is caused by an increased production of glutathione peroxidase (detectable in one's tears) which destroys the PAN. Other protective enzymes may be involved as well. Ozone, a principal damaging chemical found in air pollution, also causes the creation of free radicals as its primary method of damaging lungs. This probably leads to the increased production of protective enzymes in the lungs.
In addition, it was reported very recently in Science that ozone in the concentration range of ordinary to severe smog (0.3 to 0.8 ppm) is more toxic to cancer cells than it is to normal cells. It may be protecting some people against the development of lung cancer. This remarkable finding brings up the question whether, aside from aesthetic considerations, it is truly advisable to eliminate all air pollution!
In our opinion, studies of pollution should consider the relative biological effects of (1) potentially "desirable" pollutants that have relatively low damage potential but are inducers of protective enzymes, (2) pollutants that have a relatively high damage potential but induce protective enzymes, and (3) particularly dangerous damaging pollutants that are relatively ineffective at inducing protective enzymes. All pollutants are not equally undesirable.
A list of scientific literature on this topic is available through REASON. Send a stamped, self-addressed envelope and ask for H&W references, January.
Durk Pearson and Sandy Shaw are consulting scientists and authors of Life Extension.