I recently noticed that dying of old age is similar to a death by radiation - hair loss, weakened immune system etc. and I was wondering - Does background radiation limit our lifespan, or that of any other living creature?
There is some interesting data on the subject. People looked at the relationship between the prevalence of radon in counties in the US with the mortality due to lung cancer, and found a surprising relationship. Instead of the "more radon kills more people" correlation that was expected, there was an initial "dip" in the curve - as though "a little bit of radiation is good for you". This is phenomenological, so there is no guarantee of causality - but it does give food for thought. "What doesn't kill you makes you stronger." - could it be true in this case?
I refer you to this paper from which I will extract one quote:
and one plot:
Negative correlation. A little bit of radiation is good for you? Strange conclusion - but the data seems fairly persuasive.
Oh, I love this subject. The term here is radiation hormesis, and it's basically off-limits for nuclear regulators (If it's true, it horribly complicates the risk analysis for the use of any radiation source). The classic study comes from Taiwan http://www.jpands.org/vol9no1/chen.pdf where a number of apartment buildings were built using rebar that had been contaminated with cobalt-60 (accidental recycling). Figure 1 shows a quite remarkable decrease in cancer rates, with greater total dose and greater dose levels producing less cancer, with the effect lasting 20 years.
It's to be noted that the exposure in this case was external, rather than (for instance) ingestion of strontium-90 and caesium-137, which get concentrated in the thyroid and clearly increase the cancer risk.
As a matter of fact, I'm not at all sure I believe the results. They are too clean and the prophylactic response is both too prompt and too durable for me to accept easily. But they are certainly food for thought.
What Floris points to is not all that strange.
Living organisms exist in a state that is extremely far removed from thermal equilibrium, a lot of work is constantly being performed to maintain itself. So, even without any radiation, the body would fall apart on quite short time scales, were it not for the processes at work that do all the self repair work. Now, the capacity of the body to repair itself exceeds the minimum requirement to stay alive by quite some margin, so a little more or less radiation should not matter. However, when the damage that needs to be repaired is very low then the repair mechanisms may not work well. If the trigger for some mechanism to become active mis problem A but once it is at work it may also deal with problem B, then removing problem A may lead to problem B not being dealt with anymore.