How Does Low Level Radiation Provide Beneficial Effects?
In a recent ANS Nuclear Cafe post, I mentioned the radiation hormeis theory proposed more than three decades ago by Dr. Don Luckey, a biochemist and nutritionist who wrote a book in 1980 titled Hormesis With Ionizing Radiation. According to Dr. Luckey and a number of other researchers in the field, a small dose of radiation can provide beneficial effects.
As a former nuclear power plant operator, it was once a little difficult for me to accept that notion. After all, I had been taught – repeatedly – to keep radiation doses As Low As Reasonably Achievable. Early in my nuclear career, I was involved in planning work that resulted in a great deal of additional expenditures and manpower in order to reduce doses by a fraction of the amount that Dr. Luckey has said will not cause harm and may actually do some good.
About 15 years ago, I had the pleasure of meeting people like Jim Muckerheide, Jerry Cuttler and Ted Rockwell who introduced me to the study of the health effects of low level radiation and opened my eyes to the massive amount of peer reviewed and published information that is not widely shared or promoted. They have also helped me to find many unpublished studies – like the famous nuclear shipyard workers study that was completed but never released by the Department of Energy.
A few days ago, I asked Dr. Cuttler to help me explain just how the beneficial effects of radiation work. Here is his boiled down explanation – which I will follow with some links to far more detailed studies.
As Myron Pollycove and Ludwig Feinendegen have been explaining in their papers over the past ten years (also in my article Nuclear Energy and Health), there is a tremendous rate of endogenous DNA damage occurring in all organisms due to normal energy production, i.e., oxydation of glucose. Reactive oxygen species (ROS) attack the DNA continuously as we breathe, but each organism has powerful defences that prevent (via antioxidant production), repair and remove DNA damage. The net result is an average of one permanent mutation per cell per day.
The contribution of normal background ionizing radiation to this DNA damage rate is about ten million times less than the endogenous DNA damage rate. The effect of a small increase in the background radiation level is to produce a small increase in the DNA damage rate. This produces a low level of stress on the activity of the defences (damage-control biosystem), which stimulates this system to work harder, i.e., perform much better (producing a reduction in the DNA mutation rate). A large increase in radiation level inhibits this system (resulting in an increase in the DNA mutation rate). Harmful effects begin to surpass beneficial effects for an acute dose above 50 rad (0.5 Gy).
To summarize, the major effect of radiation on organisms (i.e., humans) is its effect on the damage-control biosystem, not its direct damage to the DNA molecules. This increase in the amount of DNA damage is relatively trivial—orders of magnitude less than the decrease in the amount of DNA damage due to the stimulation of defences (radiation hormesis).
Based upon human data, a single whole-body dose of 150 mSv (15 rem) is safe. The high natural radiation level of 700 mSv per year (70 rem/year), corresponding to a 70-year lifetime dose of 49 Sv in Ramsar, Iran, is also safe. Both these single and continuous doses are also beneficial (Cuttler and Pollycove 2009). This conclusion is applicable to humans of all ages and to sensitive, cancer-prone individuals.
Additional Reading
Observations on the Chernobyl Disaster and LNT, Zbigniew Jaworowski, Dose-Response. 2010
NCRP Report No. 136 – How to ignore data that contradict the LNT hypothesis, Dr. John Cameron, Radiation Science and Health, June 14, 2006
Setting Radiation Requirements on the Basis of Sound Science: The Role of Epidemiology, CNSC March 2011
This is important to realize that our cells are under constant stress from non-nuclear sources. Thanks Rod. That is a new insight. I updated my blog post The Time Is Right for Discussing Hormesis with this post and some of your other posts. I also added three excellent diagrams that help sort out the radiation levels and there effects on humans.
If you believe LNT, then you accept that US airlines exposing passengers to elevated ionizing radiation cause two cancer deaths per day.
The problem is that LNT cannot be falsified (or verified) due to the way it is stated, so arguing over it is a waste of time. What is needed is a solid mechanistic model that is not based of vague statistical foundations. The same is true of the radiation hormesis model, at the moment it too develops out of statistical evidence. While both sides can provide a plausible mechanism explaining what they think is happening on the cellular level, hard empirical proof is lacking.
The debate is becoming somewhat sterile at this point and something needs to be done to break the logjam. But guaranteed, no regulator is going to budge on the counter-evidence tabled to date against LNT.
Ionizing radiation might break a bond in a protein in a human cell, with no long lasting effect. Rarely, this might even cause cell death. Cell death and regrowth occurs naturally in humans, with a characteristic time of a few months, varying by organ. Even more rarely, the ionizing radiation might break a bond in a DNA strand. But DNA is the DOUBLE HELIX, with each protein paired to matching one in the other helix. This redundancy of information allows enzymes to repair broken DNA strands. DNA strand breaks are most commonly due to oxygen ions, not ionizing radiation. (This is the motivation for taking antioxidant vitamins.) The average DNA break and repair rate is about 1 per second PER CELL. There are about 100 trillion cells in the human body.
During cell division, which is more frequent during growth, the strands are separated, so the redundancy is lost and the repair rate is less. (This is the motivation for more caution for exposure of children and fetuses.)
The benefits of low-level radiation were strongly hinted at in a recently completed National Cancer Institute (NCI) study of 53,000 heavy smokers with high risk for lung cancer. http://www.fusione.altervista.org/low_dose_nuclear_radiation_may_reduce_lung_cancer_deaths.htm
A total refutation of the linear-no threshold theory (Prof. L.B. Cohen historical 2001document )
http://www.ajronline.org/cgi/content/full/179/5/1137
The LNT assumption has been falsified repeatedly from the time that it was created in the mid-1950s. What has been going on is “willful blindness” of the ever-mounting scientific evidence that contradicts it. The LNT assumption is politicized science designed to create/perpetuate the scare of even the smallest levels of (human-made) radiation. See the commentary, available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2939692/pdf/drp-08-378.pdf
@Rick
Radiation damages far more if it hits at the moment of cell division.
So stable organism’s (a.o. older persons) are far less vulnerable than organsim’s that are developing fast/
So Scherb at al showed with exceptional significance that even low level radiation below 0.5mSv/year already enhance the rate of stillbirth, congenital malformations, Down syndrome, peri-natal death, etc.
The stillbirth rate rising at a staggering ~60% per 1mSv/year rise!
Btw. this is in line with medical practise to avoid any radiation for pregnant women.