Is exposure to small amounts of radiation beneficial?

March 12, 2010

Dear Cecil:

What's the Straight Dope on radiation hormesis? From what I understand, this hypothesis rejects the current wisdom that if a lot of radiation is very bad, a little bit of radiation is at least somewhat bad. On the contrary, these folks claim a little bit of radiation might actually be good. What's up — sound science or voodoo?

Cecil replies:

You know me. I think it's voodoo. But this is one wacky-sounding theory we can't completely rule out.

Hormesis is when limited exposure to something that's generally harmful produces beneficial effects. Scientists have found many examples of this. One of the better known is fluoride: high doses are toxic, minute amounts prevent tooth decay. Other reported cases: mice exposed to dioxins show fewer cancers than normal at small doses, peppermint plants do better with a touch of herbicide, and fleas produce more offspring after exposure to the toxic heavy metal cadmium.

High doses of radiation cause cancer, of course, but some research does suggest low doses may prevent it. The idea is that low-level ionizing radiation stimulates the body's natural defense mechanisms, triggering protective processes that kill off precancerous cells and prevent cancers of all sorts. That's the reverse of the conventional wisdom, known as the linear no-threshold model, which holds that any exposure to radiation is potentially harmful — there's no threshold dose below which it's safe, much less beneficial.

Radium water tonics and such were sold in the 1920s as cures for all manner of ailments but were dismissed as quackery. A few researchers began to take another look in the 1970s, but only in the last decade or so has the idea of radiation hormesis begun to attract wide attention. For example, a 2004 study claimed more than 10,000 Taiwanese accidentally exposed for a decade or more to radioactive recycled steel used in building construction showed much lower than expected rates of cancer and congenital heart defects. The cancer rate, for example, was 3.5 cases per 100,000, compared to a normal 116 — this despite the fact that they'd gotten a pretty stiff dose of radiation, more than 1,000 times normal. A follow-up study clarified that while cancer risk declined overall, incidence of leukemia, non-Hodgkin's lymphoma, and thyroid cancer went up.

The radioactive gas radon has also attracted attention for its possible low-level benefits. A decay product of radium, radon can accumulate in buildings and in sufficiently high concentration is one of the leading causes of lung cancer. However, a 2008 study of residential radon in Massachusetts found that people who'd experienced modest radon exposure had noticeably less cancer than those with little or no exposure. Looking at a different angle, a 2000 German study found that spa therapy involving natural radon baths produced lasting pain relief in people with rheumatism.

Due to the obvious risks, most hormesis research has been conducted on animals. Some researchers claim perhaps 40 percent of animal studies show some radiation hormesis, typically conferring protection against cancer. Critics claim these studies typically focus on a narrow range of possible cancers using short-lived animals over a brief period of time, and thus don't tell you much.

Though laboratory studies of low-level radiation on humans are rare, some work has been done with human tissue samples. One study found human tissue exposed to low-level radiation and then given a high dose of X-rays showed less DNA damage than would be expected after the X-rays alone. On the other hand, a study comparing two groups of people in China, one receiving three to four times as much background radiation as the other, found no differences in cancer rates. Then again, the radiation levels were so low that the expected difference was only around 1 to 2 percent.

In short, research to date has been inconclusive — perhaps par for the course on cutting-edge topics. For now, research bodies such as the UN Scientific Committee on the Effects of Atomic Radiation and the National Academy of Sciences are sticking with the assumption that there's no minimum safe level of radiation. My guess is that even if radiation hormesis turns out to be real, you'll solve some problems at the expense of making others worse. Suppose you're the surgeon general and a blue-ribbon panel tells you a modest dose of goboomium in the water supply will drastically reduce most cancers while increasing leukemia, non-Hodgkin's lymphoma and thyroid cancer. What do you recommend we do?

Medical questions we're still thinking about

Dear Cecil:

Assume one can take one's eyeball out of its socket and hold it a couple of inches away while still connected to the brain by the optic nerve. Now, if you turn this eye around so it is looking straight into your other eye, what would you see?

Dear Cecil:

Do you know if anyone has ever performed emergency back surgery on themselves?

Dear Cecil:

Is there a "cure" for the dumb ass?

Cecil replies:

One can only hope.

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Aurengo, Andre et al. Dose-effect relationships and estimation of the carcinogenic effects of low doses of ionizing radiation Académie des Sciences and Académie Nationale de Médecine, France, 2005.

Cardis, E. et al. “The 15-Country Collaborative Study of Cancer Risk among Radiation Workers in the Nuclear Industry: Estimates of Radiation-Related Cancer Risks” Radiation Research 167 (2007): 396-416.

Chen, W.L. et al. “Is Chronic Radiation an Effective Prophylaxis Against Cancer?” Journal of American Physicians and Surgeons 9.1 (2004): 6-10.

Elliott, K.C. “Respect for lay perceptions of risk in the hormesis case” Human and Experimental Toxicology 28 (2009): 21-26.

Feinendegen, L. E. “Evidence for beneficial low level radiation effects and radiation hormesis” The British Journal of Radiology 78 (2005): 3-7.

Hwang, S-L et al. “Cancer risks in a population with prolonged low dose-rate g-radiation exposure in radiocontaminated buildings, 1983 – 2002” International Journal of Radiation Biology 82 (2006): 849-858.

Kaiser, Jocelyn “Sipping from a Poisoned Chalice” Science 376 (2003): 376-378.

Monson, Richard R. et al. Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 Washington, D.C.: National Academy of Sciences, 2006.

Parsons, Peter A. “Hormesis: an Adaptive Expectation with Emphasis on Ionizing Radiation” Journal of Applied Toxicology 20 (2000): 103-112.

Scott, Bobby R. “It’s time for a new low-dose-radiation risk assessment paradigm – one that acknowledges hormesis” Dose-Response 6 (2008): 333-351.

The Straight Dope: What poisons can I safely take to build immunity to toxic substances.

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR): UNSCEAR 2000 REPORT Vol. II: Sources and Effects of Ionizing Radiation: Annex G: Biological effects at low radiation doses.

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