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A new study from MIT scientists suggests that long-term exposure to low-radiation poses no risk of DNA damage for mice (it is also important to note that mice are unusually susceptible to cancer). So apparently there may be a threshold for radiation damage to DNA.

But is this study conclusive? What are some other studies that show the biological effects of long-term low-dose radiation on DNA?

There are some studies that do show increased rates of cancer in frequent flyers. So are are we going to reconcile this finding with the finding above?

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Can you say that anything in science is conclusive? –  kmm May 16 '12 at 18:55
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@Kevin Yes of course. Why not? “conclusive” doesn’t mean 100% sure – otherwise nothing would be conclusive, thanks to Gödel’s incompleteness theorem. It just means “reasonably sure” given some fitting threshold. –  Konrad Rudolph May 17 '12 at 13:59
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up vote 4 down vote accepted

I agree with @Kevin - there are no ultimate statements in science. The answer is 'its all relative'.

With radiation and risk, more radiation means more risk of cancer or any number of other types of damage that can result. The question is is this significant? And this is a somewhat subjective question.

When someone says:

'there is no health risk from XYZ'

what they mean is..

"to the extent that we can determine, we can't see any more chance of adverse health if you are exposed to XYZ conditions than if you weren't"

DNA damage happens all the time. The frequent flier study you cite is trying to see if the additional exposure to cosmic radiation while flying, which is largely blocked by the atmosphere, causes a change in the rate of some cancers.

Radiation and cancer is like a lottery. If you buy just one ticket you might win. If you step outside, the thousands of extra gamma rays you get outside might start a cancer that will eventually take your life. If you buy 20 million tickets you will very likely win. If you hang out next to high levels of radiation, even for a short while, you will get so much damage you will not live long.

Its difficult to study the effect of low levels of radiation. The lower the levels of radiation we are asking about, the longer you will have to wait to see if there is an effect. If 10% more people get cancer, you have a very real concern that some of these folks might have done something else, like sunbathe or live in a poorly ventilated basement for too long.

The real question is, what is significant? I once saw a 60 minutes segment where a dermatologist said that she simply never directly exposes her skin to direct sunlight. I'm betting she never got a melanoma. She carried a parasol and wore light gloves outdoors. (sorry I can't find the link) She was at least in her 50s and she had the skin of a teenager. I still go out in the sun. I assume my risk of melanoma is 5-10 times more than hers was (this was a pretty old broadcast). (mine is 0.03% in the next 5 years btw). Its just not worth it to me.

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See my answer to Kevin’s comment. This is a red herring, “conclusive” isn’t the same as “ultimate statement”. –  Konrad Rudolph May 17 '12 at 14:00
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In the astrobiology community, radiation is a ubiquitous factor in the survival of life in space. It's the current understanding that, while high doses of radiation over a short period of time are lethal, an equivalent dose over a much longer time period (maybe 1000x longer) is much less harmful.

The basis for radiation lethality lies in the ability of high-energy particles (that's what radiation is) to damage DNA. When DNA gets damaged, there are some issues:

  1. The normal, regular structure of the molecule gets disturbed. The genetic code is a very delicate structure. The code is linearly sequence-dependent, and it is only singly redundant (there are two strands of DNA, so if one strand becomes damaged, it can be recopied from the other one).
  2. Our cells are under unrelenting barrage of oxidative stress, EM radiation, radioactive radiation and physiological stress--this is no exhaustive listing of the constant fight our bodies' cells put up all the time. There are repair mechanisms in place to automatically fix the damage done by high-energy radiation, and if it turns out that a particular cell has sustained too much damage--well, it commits suicide. This process is called apoptosis and its importance ranges from proper embryonic development to prevention of cancers.
  3. In short, there are two ways that excess radiation can cause an organism to die: a) DNA and cellular damage to an irreparable extent, and b) mutagenesis to cause cancers and other cell-cycle diseases.

We don't quite know the full extent to which we can expose our bodies to long-term high-energy radiation, but the answer is sure very complex. Different tissues, cell lines, and regions of the body receive and cope with radiation in very different ways.

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