Revival: Biological Effects of Low Level Exposures to Chemical and Radiation (1992)

HYPOTHESES ON LONGEVITY HORMESIS 33

There are blossoms all around us with the

colors of our dawn,

And we live in borrowed sunshine when

the day-star is withdrawn.

Oliver Wendell Holmes, Sr.111

If it is assumed that the Napierian logarithm of the hazard function,
termed the Gompertzian, is proportional to the mean intensity of physio­
logic injury for homogeneous, laboratory populations of eutherian mam­
malian species housed under good, uniform laboratory conditions, a simple
and convenient method is afforded the investigator to explore the time
course of injury accrual and/or disposal. In animal populations, a phenom­
enon of unknown mechanism, termed longevity hormesis, has been demon­

strated to reversibly reduce Gompertzians to values below those of control
populations. Presumably, this is mediated through a temporarily lessening
in one or more types of injury, and is initiated by exposure of organisms to a
variety of different stimuli. This response of Gompertzians is distinctly
different from that achieved through caloric restriction. Exposures of pop­
ulations of eutherian mammals to external stimuli, in addition to enhancing
life span through longevity hormesis and/or caloric restriction, can also
decrease longevity by causing either reversible or irreversible toxicity.

Analyses of several data sets suggest that all these actions superimpose their
injury promoting or decreasing effects onto the hitherto state of the organ­
ism. Evidence for the existence of longevity hormesis in humans is fragmen­

tary and controversial at best.

ACKNOWLEDGMENTS

The author wishes to express his deep appreciation to Frank Hoke, Pat
Neafsey, and Gary A. Thompson for their helpful comments in reviewing
this chapter.

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