Well, I am impressed how conservative columnist Ann Coulter finds ways to make headlines. The darling of the radical right ventured into science journalism the other day, when during an interview with Fox News's Bill O'Reilly, she said that radiation above the government cutoff is good for you.
She was promoting her latest column on her Web site, "A Glowing Report on Radiation". She was trying to explain the concept of hormesis without fully understanding it.*
Developed by Edward Calabrese of the University of Massachusetts Amherst, hormesis is a kind of Nietzsche toxicology: what doesn't kill you makes you stronger. The idea is that low levels of toxin can stress your body like exercise does, stimulating immune and cell-repair systems.
The evidence, based on lab experiments done on mice, zebra fish and other non-humans, is intriguing. But the theory is incomplete, hard to study, often confusing, and impossible to generalize as a basic biological principle. For instance, dioxin shows hormetic effects but only when the data includes all cancers, not specific types of cancer.
Part of the trouble lies with measuring the effects of extremely low doses. As PZ Myers ably describes in his blog take-down of Coulter's column, separating signals from noise is difficult at that level.
As Myers puts it: "In the low-dosage regime, these responses get complicated at the same time the data gets harder to collect." He likened the situation to driving on a winter road: when you see an ice patch, you slow down, cutting your risk of an accident. But that doesn't mean that a little ice prevents accidents.
No good evidence exists for hormesis in human epidemiology, either. In her column, Coulter mentions that Japan's atom bomb survivors lived longer than average. But that longevity has an easy explanation: the survivors received greater medical care over the course of their lives after the bombing.
And although she correctly points out that identifying Chernobyl radiation deaths is tough, her analysis on the excess thyroid cancer cases is strange: she concludes that they resulted from iodine deficiency. I presume she means that more iodine (like what you might get in potassium iodide pills) would have prevented the radioactive isotopes created by the Chernobyl meltdown from getting into the thyroid. So yeah, it's the diet's fault--riiiiight.
Most researchers remain skeptical of hormesis, and no safety agency can in good conscience change dose safety levels based on controversial animal data. Besides, controlling doses near fallout zones would be impossible.
You can read more about how radiation threatens health here.