Saturday, August 20, 2011
Hormesis - A little radiation may be a good thing
Last Thursday, my wife and I gave a presentation to the new students in the Honors College at WSU on the common reading book, Physics for Future Presidents. One large chunk of the book discusses nuclear power and its risks. When extrapolating to low dose, the author is careful to always state "assuming the linear hypothesis."
This got me thinking about an article in Scientific American that I read back in 2003 on the topic of Hormesis. The idea is that toxins might actually be beneficial when taken in low doses. As an example of Hormesis, exercise wreaks all sorts of havoc on the cellular level, but is healthy in moderation. The explanation is that the body's response in repairing the damage does some good that goes beyond the status quo. At higher levels of exposure, the body cannot keep up with the damage, and toxic effects become - well, toxic.
The red curve in the figure shows the linear hypothesis; the toxicity of a toxin, quantified in terms of the death rate, increases with dose. Hormesis, shown in green, yields a benefit at low exposure levels. Serious scientific studies are finding a hormesis response in many toxicological studies.
Hormesis may describe the effect of ionizing radiation on living creatures such as humans (see the references below). Karl Grossman furiously protests on the anti-Nuke website NuclearFREEPlanet.org. He sees these studies as an obvious ploy by nuclear scientists to pollute the planet, "These scientists don't just want to minimize or even flatly deny the deadly impacts of radioactivity - they want people to think it's healthy." What if it is actually healthy?
Our presentation to the students of the Honors college focused on the notion that decisions that are made based on the facts have better outcomes when not clouded by ideology. We should not bash science just because its conclusions weaken those arguments that support our beliefs.
My point in using this example is not to be an advocate for nuclear energy, nor is it to support the hormesis hypothesis. Rather, it is to illustrate the pitfalls of clinging to an ideology. If the best evidence shows that low levels of radiation is safe and potentially beneficial, then why not loosen standards to reflect the best science?
Some readers may find these arguments reminiscent of the homeopathy hypothesis, that ingesting toxins at levels of zero concentration can cure various ailments. There is absolutely no evidence for homeopathic effects. Wikipedia devotes a page to Jacques Benveniste, who purported to observe such effects (published in the prestigious journal Nature), but whose work has been discredited many times since (blue dot in the figure). A site visit by a team assembled by the editors of Nature at the time of the report in 1988 found serious procedural problems that explained the spurious result.
Sadly, homeopathic remedies are found on the shelves of my local pharmacy and are even covered by the health plans of many countries. I would venture a guess that there is a large overlap between people who use homeopathic remedies and those who deny hormesis based on their anti-nuke sentiments. If so, they may be wrong on two counts.
At the risk of accusations of being pro nuclear, I will post some interesting statistics on radiation, and a comparison of the dangers of various energy sources including nuclear power. Until then, I encourage you to read the informative links in this post. For someone with a more serious interest, I recommend the articles in the reference list, which appear in hard-core scientific journals. If you are left with a desire to dig deeper, there are several hundred more articles on the topic. But, stay away from ideological websites, unless your aim is to feed your ideology rather than learning the truth.
Title: Hormesis: The dose-response revolution
Author(s): Calabrese EJ; Baldwin LA
Source: ANNUAL REVIEW OF PHARMACOLOGY AND TOXICOLOGY Volume: 43 Pages: 175-197 DOI: 10.1146/annurev.pharmtox.43.100901.140223 Published: 2003
Title: The frequency of U-shaped dose responses in the toxicological literature
Author(s): Calabrese EJ; Baldwin LA
Source: TOXICOLOGICAL SCIENCES Volume: 62 Issue: 2 Pages: 330-338 DOI: 10.1093/toxsci/62.2.330 Published: AUG 2001
Title: Hormesis: A highly generalizable and reproducible phenomenon with important implications for risk assessment
Author(s): Calabrese EJ; Baldwin LA; Holland CD
Source: RISK ANALYSIS Volume: 19 Issue: 2 Pages: 261-281 DOI: 10.1111/j.1539-6924.1999.tb00404.x Published: APR 1999
Title: Evidence for beneficial low level radiation effects and radiation hormesis
Author(s): Feinendegen LE
Source: BRITISH JOURNAL OF RADIOLOGY Volume: 78 Issue: 925 Pages: 3-7 DOI: 10.1259/bjr/63353075 Published: JAN 2005
Title: Multiple stressors in Caenorhabditis elegans induce stress hormesis and extended longevity
Author(s): Cypser JR; Johnson TE
Source: JOURNALS OF GERONTOLOGY SERIES A-BIOLOGICAL SCIENCES AND MEDICAL SCIENCES Volume: 57 Issue: 3 Pages: B109-B114 Published: MAR 200
Title: RADIATION HORMESIS - ITS EXPRESSION IN THE IMMUNE-SYSTEM
Author(s): SHU ZL; LIU WH; SUN JB
Source: HEALTH PHYSICS Volume: 52 Issue: 5 Pages: 579-583 Published: MAY 1987
Title: Exercise and hormesis: oxidative stress-related adaptation for successful aging
Author(s): Radak Z; Chung HY; Goto S
Source: BIOGERONTOLOGY Volume: 6 Issue: 1 Pages: 71-75 DOI: 10.1007/s10522-004-7386-7 Published: JAN 2005
Title: Effect of a continuous gamma irradiation at a very low dose on the life span of mice
Author(s): Caratero A; Courtade M; Bonnet L; et al.
Source: GERONTOLOGY Volume: 44 Issue: 5 Pages: 272-276 DOI: 10.1159/000022024 Published: SEP-OCT 1998