Medicine, science, and public policy are driven by competing theories about how our bodies react to various substances.
The U.S. Environmental Protection Agency (EPA) bases its decisions on a linear no-threshold (LNT) model, which assumes if a lot of something is bad for us, a little is bad as well. When laboratory rats die of chemical megadoses and EPA concludes humans will be hurt by minuscule doses of the chemical, that is the LNT model at work.
A competing theory is “hormesis,” which holds that when a subject is exposed to small doses of something, one often observes the entirely opposite effect than when large doses are applied.
Hormesis is the principle behind vaccination. When someone is vaccinated with a small amount of an inactive virus, he is protected from the disease itself. Similarly, exposing laboratory mice to small doses of gamma ray radiation shortly before exposing them to large doses makes it less likely the mice will develop cancer.
The biological mechanisms for hormesis are not well understood, but it appears likely that a low-dose application of a toxin may trigger certain repair mechanisms in the body.
Hundreds of experiments document the hormesis effect. Many of the most important experiments were compiled by Walter Heiby in his 1,200-page book, The Reverse Effect (Mediscience, 1988). The popularization of the term hormesis was brought about by T. R. Luckey in his 1982 paper on this subject in the Journal of Health Physics.
Much of Luckey’s work focused on radiation. A clear understanding of this field followed the recorded health history of Japanese citizens living in proximity to the war-ending atomic bomb drops on Nagasaki and Hiroshima.
People in close proximity to the blasts died quickly, and for those a short distance away, cancer rates skyrocketed. But citizens at the outer ring of measured radiation, where exposure was present but very small, experienced lower cancer rates than those experienced by unexposed Japanese.
In her 1984 book, The Dose Makes the Poison (Wiley), Alice Ottoboni noted, “every toxicologist who has been engaged for any period of time in research into chronic toxic effects of chemicals has observed that animals in the group with the lowest exposure to the test chemical grew more rapidly, had better general appearance and coat quality, had fewer tumors and lived longer than the control animals.”
It is common for most inexperienced scientists to consider such observations as aberrations in their data or flaws in their experimental design. They rarely draw attention to these findings, for fear of having their competence questioned when they can’t explain them.
With the confidence that comes with experience, however, this becomes a common point of discussion among toxicologists. Nevertheless, it rarely finds its way into the text of their published articles in science journals, though it is frequently evident in their data tables.
Most laboratory scientists now recognize high-dose exposures cannot predict low-dose results. But EPA continues to make public policy based on the flawed LNT model, setting standards for such things as arsenic in drinking water and particulate matter in the air by assuming every last molecule is dangerous to human health and must be removed.
With respect to radiation exposure, the LNT model would appear not only incorrect but in fact counterproductive. Many women avoid important mammograms because they fear low-level radiation exposure. Some people avoid dental X-rays for the same reason.
Similarly, the important contributions nuclear power could make around the world are impeded by fear of low-level radiation that may exist in the vicinity of the power plants. Ironically, nuclear power plants produce less radiation in their surrounding areas than do plants fired by coal, which is mined from beds that have naturally radioactive material.
Unlike the LNT model employed by EPA, the hormesis theory “rings true” for most of us. We know, for example, that many vitamins that are of great value in small quantities are hazardous in large doses. Most of us are familiar with the common saying “too much of a good thing.”
A rather amusing but instructive way of looking at the reality of hormesis is described by Ed Hiserodt in his 2005 book, Underexposed: What If Radiation Is Actually Good for Us? (Laissez Faire Books).
Hiserodt asks us to recognize that if 100 percent of people who fall 100 feet to a concrete floor are killed, and 50 percent of people who fall 50 feet to that same floor are killed, we might logically think that 25 percent of those falling 25 feet would meet their end.
But going further in the linear relationship we begin to see the absurdity of the LNT model. Would we expect 1 percent of those falling one foot to die? And if 10,000 people stepped off a six-inch curb, would we expect 50 to die?
Everyone sees the absurdity of this linear relationship, yet we are convinced it is true for so many other risks, such as exposure to secondhand smoke.
Consider some common examples of hormesis in human experience.
- Vitamins and trace minerals clearly show the difference a dose makes. Arsenic and selenium are deadly poisons, but in trace amounts they are necessary to human life.
- Some sunlight is necessary for the production of vitamin D in the body, but too much can lead to skin cancers.
- Some noise can be soothing and healthful, while long exposure to loud noises can cause mental confusion and loss of hearing.
- Most athletes are well aware that in training, some pain may be required to make gains, but too much pain indicates ruptured muscles and torn ligaments.
- Lack of stress makes people lethargic, while too much stress can cause permanent physical and mental harm.
Clearly, hormesis is quite real. By contrast, the linear no-threshold model utilized by EPA is unrealistic, inaccurate, and at times, downright dangerous.
Jay Lehr, Ph.D. ([email protected]) is science director for The Heartland Institute.