Friday, February 19, 2016

Effects of Radiation on the Life Span of Mice

Surely if ionizing radiation has beneficial effects on growth rate and the immune system competence of mice, as evidenced by a decreased susceptibility to cancer, it ought to have a positive effect on life span. As several studies demonstrate, this is indeed the case.

A 1983 investigation by J.B. Storer [Storer, J.B., et al. Life shortening [sic] in Balb/C mice following brief protracted, and fractionated exposures to neutrons. Radiation Research, 96, 396, 1983] was cited by Luckey as an example of how hormesis effects are often overlooked by researchers who are expected a bio-negative response from radiation. [Radiation Hormesis, 1981, pp 46, 50.]

The authors ignored a peaking of longevity between 5 and 10 cGy, hopefully not in any attempt to be fraudulent or unethical, but probably because it would have appeared anomalous in terms of the LNT.

It is an earlier study [Sacher, G.A. and Grahn, G. Survival of mice under duration-of-life exposure to gamma rays. Journal of the National Cancer Institute, 32, 277, 1964] - which most certainly gave unintended results - that is of considerable interest to hormesis researchers. Life spans of mice - 90 in a control group, and 90 to 120 in four exposed groups - are plotted in Figure 10 on the basis of daily exposures to cobalt-60 gamma radiation. Exposures, which began 100 days after birth, were continued until the death of the specimen.

Caption for Figure 10 Life Span for Irradiated Mice  Source: Sacher, G.A., and Grahn, G. Survival of mice under duration-of-life exposure to gamma rays. I. The dosage-survival relation and lethality function. Journal of the National Cancer Institute, 32, 277, 1964; also ANL Report 6971, 1964, p 94.

Anti-nuclear activists, "animal rightists," and "popular wisdom" would predict dire consequences for test animals subjected to such huge doses of radiation every day of their lives. But this study offers substantial evidence that mice receiving 1,000 times their normal background dose had the longest life spans. [It is my understanding that similar results were reported by a researcher named Searle in 1964, but I have not been able to obtain any more information.] You might recall that, in the earlier discussion of growth rate, the optimum was also 1,000 times normal background.