Could a little poison be a good thing? discusses hormesis, the notion that “moderate doses of bad things like radiation and toxins can improve health”:
Evidence is building for hormesis, the theory that suggests that moderate doses of bad things like radiation and toxins can improve health. Interestingly, much of the evidence has been around for a long time but it has been ignored because the focus was on proving the harm that toxins can cause and because low-dose effects are, by their nature, harder to identify so positive effects at low doses were typically discounted.
The Scientific American article he cites, Nietzsche’s Toxicology, explains:
The stress triggers cellular repair and maintenance systems. A modest amount of overcompensation then produces the low-dose effect, which is often beneficial.
This idea may sound bizarre, but such adaptation to stress is common, says physiologist Suresh Rattan of Aarhus University in Denmark. Exercise, for instance, plays biochemical havoc with the body: starving some cells of oxygen and glucose, flooding others with oxidants, and depressing immune functions. “At first glance, there is nothing good for the body about exercise,” he notes. But even couch potatoes know that moderate exercise is worthwhile. Rattan says that the cellular insults from exercise prompt the defense system to work more efficiently.
Some fascinating examples:
For example, the prevailing theory is that any increase in radiation exposure increases the risk of cancer. But biologist Ronald Mitchel of Atomic Energy of Canada has shown that a single low dose of ionizing radiation stimulates DNA repair, delaying the onset of cancer in mice; high doses produced the opposite effect, as expected. Prolonged exposure to extreme temperatures is also harmful, but Rattan has found that heating up human skin cells to 41 degrees Celsius (106 degrees Fahrenheit) twice a week for an hour slows aging in the cells.
Even well-established environmental headaches display some hormesis. The definitive rat study that linked high doses of dioxin to cancer, published in 1978 by Richard Kociba of Dow Chemical and his colleagues, also found that low doses reduced the incidence of tumors.
Here’s where it all gets controversial:
Calabrese suspects that in many cases, the benefits of hormesis may occur at levels higher than the recommended safe doses for humans.