2013-08-14
How many linear relationships in biology persist over more than 6 orders of magnitude?
Whether a given dose is hormetic or deleterious should depend on the stress on the animal at the time of exposure. I conjecture that wartime stress could be responsible for deleterious effects in Japanese bomb survivors at ~ 100mSv, compared to other exposure cases that suggest hormetic effects at that dose.
The doubling dose for double-strand breaks is about 1.5 Gy per cell cycle.[^1] That is, ROS from normal metabolism are worth about 0.3 Gy/hour. DNA repair machinery is nearly at capacity at that level, so an additional 1.5 Gy can be deadly. Exercise seems to derive its benefits from stimulating the same systems [^2][^3] and whether it is good or bad also depends on one's existing stress level. Exercising a fatigued person is deleterious, but exercising a sedentary person is beneficial.
If oxidative stress is hormetic, antioxidant supplements may be harmful.[^4]