Missing the point

Tyler Cowen, upon reading the latest blurb from the scientific community about DNA repair relative to X-ray dose, thinks that his "crank theory" that low level X-rays are worse for you than high level has been vindicated.

From the link provided in his post, the German researchers that performed the experiments found that cells repair DNA damage caused by X-rays at a high rate, but below a certain dosage (that is, the dosage normally given on routine x-rays), the cells put off the repairs for days, or not at all. Tyler believes that this means, quixotically and ironically, that low dose is worse for you than high dose, since DNA damage isn't repaired as fast (or at all) at low doses, and unrepaired damage can cause cancer.

Not so fast, Tyler. The blurb's authors go on to note, rather importantly, that DNA repair is not risk-free and can incorporate errors as well. DNA repair enzymes are notoriously more error-prone than ones used in replication (for obvious reasons- speed tradeoffs being the main one), and the authors quite correctly point out that the non-repair for slight damage may be evolutionarily favored as part of a long worked-out cost-benefit analysis. Sending your notoriously sloppy repair enzymes out to fix every nick and dent will, in the long run, mean more mutation, not less. That the cells exposed to high doses repair immediately is simply a recognition that the damage is extensive enough that there is more benefit to fixing it (sloppily) than to let large swathes of cells die (as would be the case if each individual cell did not repair).

Indeed, the non-repair allows the cells to figure out for themselves which ones need to just die and be replaced- using the radiation damage as a spur to evaluating the health of any given cell. If a few cells are disrupted enough by the damage that they must self-destruct, they are replaced via cell division- which involves DNA replication that has far greater fidelity than DNA repair. This could explain why, in some cases, low doses of radiation have shown to spur healthier growth among animals and plants (as have low doses of other normal environmental poisons)- not enough to kill, but enough to gently cull the substandard cells, forcing the organism to replace them with hardier cells.

Thus, Tyler has is somwhat backward. The news is that, more than ever, low-dose radiation is better for you than high-dose. Stop being cranky, Tyler! Get those x-rays.

To tie this in with the themes of the blog (too late?), I'd point out that biological systems are wonderful examples of individual entities working as parts of larger organisms via complex, indirect signalling mechanisms. That, and I used to be a molecular genetics grad student, so this is my old bag. (heh)

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Did you mean to comment on

Did you mean to comment on the post above? ^_^ Most biological systems aren't a democracy at all...

Sweet article. Great find.

Sweet article. Great find. Might I ask you to elaborate on "mass democracy", however, and what would be your alternative?