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Is radiation beneficial?

Everything in moderation — even radioactivity.
bob_berman_2009
If we’re ever to colonize other planets, we’ll have to deal with increased radiation environments. Starting in 1969, 24 astronauts ventured beyond Earth’s atmosphere and magnetosphere, leaving behind all layers of cosmic ray protection. U.S. astronaut Shannon Lucid cites this hazard as the biggest challenge for manned space exploration.
  

It may already have cost some astronauts their lives. Five of the original space pioneers have died of cancer. Alan Shepard publicly wondered if his Apollo radiation exposure had given him the leukemia that ultimately killed him. And studies show that radiation is particularly bad for the heart.

Many of us have a personal stake in this issue. Some of us have undergone whole-body CT scans, each of which could have delivered as much radiation as Hiroshima survivors received a mile away from ground zero.

Should we worry? Maybe, but maybe not. Nuclear safety experts have long known about lethal radiation doses, after unfortunate accidents involving workers assembling nuclear weapons and several instances when uranium-235 in power plants went supercritical. There have even been several suicides and suicide attempts (a radiological worker in Moscow, a radiographer in the U.K.), as well as murders (Alexander Litvinenko, Roman Tsepov, Vladimir Kaplun) using radioactive materials. All this has confirmed that exposure to 1,000 rems (a common but now antiquated classification; 1 rem equals 0.01 sievert, the modern SI unit) is usually fatal. For comparison, astronauts landing on Europa’s icy surface would receive 540 rems (5.4 Sv), which is lethal in just a couple of hours.

Accidents such as Chernobyl, plus studies of the Nagasaki and Hiroshima survivors, show that sublethal doses can result in cancer 20 years later. So early on, health physicists created a paradigm now known as the LNT — the linear no-threshold model — by graphing fatalities and cancers caused by various radiation doses, working backward to assess the consequences of very small exposures. 

They guessed that there is no safe threshold for radiation: No matter how small the dose, some DNA will be damaged, and some percentage of people will eventually get cancer. If this is true, then we should be careful about getting CT scans. We might even watch how many bananas we eat, since each gives us more radiation from potassium-40 than we’d get by living next to a nuclear power plant for a year (though still just 1/100th the daily dose we get simply by living on Earth).

BobBerman0418
Water surrounding the core of the Advanced Test Reactor glows bright blue because of an effect called Cherenkov radiation.
Argonne National Laboratory
To test their hypothesis, epidemiologists studied large groups of people exposed to small amounts of radiation. For example, there is a decade-long medical survey of 70,000 residents living near a radioactive thorium-contaminated black sand beach in Kerala, India.

They got a surprise. Cancer rates in Kerala residents, and in Hiroshima, Nagasaki, and Chernobyl survivors, are far below the rates predicted by the LNT model. In some cases, the cancer rate was less than in control groups. Their radiation exposure had apparently protected them from cancer!

Taken aback, researchers revisited animal studies that had indeed showed a protective, beneficial effect from low radiation doses. Could small radiation doses actually be good for you? This possibility, called radiation hormesis, has a sound biological basis. All animals are exposed to continuous low-dose radiation from cosmic rays and such. The body is accustomed to repairing such genetic damage. When rats are exposed to low-dose radiation, it seems to prime, harden, and shield them from the results of getting a later, much larger radiation zap. They’re even protected from other carcinogens.

If true, radiation hormesis means that, even should Europa remain off-limits, astronauts might do fine on the Moon or Mars. Back home, there’s no reason to decline dental X-rays.

The idea that it’s healthful to get small doses of something that would harm you in higher amounts is not new. It’s the founding principle of homeopathy. It certainly applies to things like fasting, stress, and iron or iodine supplements.

In 2005, the British Journal of Radiology published an article by Ludwig E. Feinendegen, M.D., a member of the Medical Advisory Board at Advanced Medical Isotope Corp., concluding, “The linear-no-threshold hypothesis for cancer risk is scientifically unfounded and appears to be invalid in favour of a threshold or hormesis. This is consistent with data both from animal studies and human epidemiological observations on low-dose induced cancer. The LNT hypothesis should be abandoned and be replaced by a hypothesis that is scientifically justified.”

More studies are underway. One involves putting animals in a zero-radiation environment shielded even from the normal earthly background of 360 microsieverts per year. Will they die sooner when they’re deprived of all radiation?

It’s too soon to know. The biggest health organizations continue to advise avoiding unnecessary radiation, and hormesis remains controversial. But even at this early stage, it’s amazing enough to deserve our attention, since it may affect the planetary destinies of the human race.

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