that radiation hormesis is real. for an explanation let’s consider the case of cancer in more detail. the reason that the incidence of cancer increases as people age is not because their cells lose the ability to repair dna, but rather because a whole set of mutations must accumulate over time for cancer to develop. for the purpose of this discussion, let’s say there are five necessary mutations: A, B, C, D and E, that must occur in the same cell to convert it from the healthy to malignant state;
over time, each of these mutations randomly accumulate in cells; again, for the purposes of this discussion, let’s assume that by age 65, mutation A has occurred in one out of every 1000 cells of your body. however, mutation A alone cannot cause cancer so you’re OK.
now let’s consider that mutation B is independently occurring at the same rate and slowly accumulating in your cells. so when you’re 65, one out of 1000 of your cells will also have this mutation, but (once again), that’s OK because mutation B, by itself, does not cause cancer. but, if 1/1000 cells has mutation A and 1/1000 cells has mutation B, that means that (1/1000) x (1/1000), or 1/1,000,000 (one in a million) cells will have both mutation A
and mutation B. such as cell, while still not cancerous, is nevertheless a step further along the pathway to becoming so.
we can repeat a similar analysis for mutations C, D, and E. at the end, we need to calculate what the chance is that all mutations will occur in a single cell. continuing the numbers from our example, that would be (1/1000) x (1/1000) x (1/1000) x (1/1000) x (1/1000), or 1 out of 10e15 cells (that’s one out of a quadrillion cells). a cell with all five mutations would be a cancer cell, grow into a tumor, etc. etc.
so what do the above numbers mean (part 1)? if you have 10e13 cells in your body (not an exact, but a reasonable estimate), your chance of getting the type of cancer in this example at the age 65 would be (1/10e15) x (10e13), or 1/100 (one in a hundred). (incidently, when you hear of cancer-causing genes, basically what that means is that one of the five cancer-causing mutations occurs in the germ line, and is therefore in all your cells. in this case, only four mutations need to arise in the same cell to give you cancer, thereby increasing the odds 1000-fold, or from one in a hundred to 10 to 1, that you'll get this type of cancer).
so what do the above numbers mean (part 2)? another implication is that if you can slow down the rate at which mutations occur, the older you will be before you get a particular type of cancer. ideally, you’ll be so old that you’ll die from some other cause. anyhow, the vast majority of dna damage (which leads to mutations if unrepaired) is caused by normal metabolism. also, the bulk of damaged dna is rapidly repaired by several dozen different types of dna repair enzymes found in each cell. now is where the helpful effects of radiation come in. at certain doses, radiation will transiently raise the level of dna damage (by a few percent over background, which is really no problem for a cell because it’s used to repairing dna and the radiation-induced damage will be repaired in a few hours). but, at the same time, the radiation stimulates the production of dna repair enzymes. generally these higher levels of repair enzymes persist in cells for several days or weeks (i.e., long after the dna damage caused by the radiation is repaired). consequently, the naturally-occurring dna damage is repaired more effectively during this time period, and the onset of cancer is slowed.
of course proving that radiation hormesis is effective is almost impossible. from the above discussion, it can be envisioned that a controlled “clinical” study would involve following cohorts of persons regularly exposed to hormetic doses of radiation with those who weren’t (variability in environmental levels of radiation makes controlled exposure to fairly low, hormetic doses, almost impossible however). further, such a study would have to be conducted for, say, 65 years. and then repeated in triplicate. clearly, although the cellular basis of hormesis is well established, the study of the effects of radiation hormesis in people is at a very elementary stage and not enough is known about the exact doses needed for beneficial effects, or when the amount crosses over to being harmful. therefore, it’s likely not a good idea to go and deliberately expose yourself to radiation at this point (and, in any event, you really don’t have to since all those coal-burning power plants do it for you)
if you wish to find out more, i urge you to check out the peer-reviewed literature by doing a search at the national institute of health’s PUBMED site:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=Search&DB=PubMed
(1000+ posts)
