HYPOTHESES ON LONGEVITY HORMESIS 21curves in Figures 1.6 and 1.7, an equivalent method was used (Equations A-
2 and A-4 of Neafsey et al.24). In comparing Figures 1.6 and 1.7, note the
differences in the curves for calorically restricted animals relative to those
experiencing longevity hormesis; they are distinctly different in relationship
to the control group.
Figure 1.8 provides another example of a system (male LAF1 rats receiv
ing 0.11 rad/day 7 -radiation) in which longevity hormesis exists in the
absence of observable toxicity.25 This is in contrast to Figure 1.9, which
illustrates the effects of several doses of 7 -radiation on Gompertz plots.25 At
the 0 .11 rad/day dose, there is both minor longevity hormesis and toxicity;
however, in this study, data from both genders were pooled, whereas in
Figure 1.8 only data from male animals are illustrated. Note in Figure 1.9
how increased doses of radiation induce toxicity to the point that longevity
hormesis is obscured. This is a major problem in long-term toxicity studies,
which typically employ relatively high doses of toxicants (generally about
12.5 to 100% of the maximum tolerated dose per day) in an attempt to
assess risk at much lower doses.
Although both Boxenbaum et al.18 and Neafsey 27 have recently addressed
the problem of potentially overlooked longevity hormesis, the risk assess
ment community has failed to give it serious consideration. Previously,
Smyth 85 had taken notice of the fact that low doses of otherwise toxic
substances can be beneficial. His reward: the epithet “Dr. Smyth and his
fellow poisoners.”86 Although the scientific community envisages itself as
the epitome of institutionalized rationality,87 many researchers have noted
Figure 1.8. Gompertz plots for control and 7-radiation treated male LAF1 mice. The
treated group received 7-radiation at a dose of 0.11 rad/day (administered
over 8 hr), begun at 1 month of age and continued throughout life. Time on
the abscissa refers to the period following initiation of exposure. Note the
classic longevity hormesis pattern, with no apparent concomitant toxicity.
The theoretical lines were obtained by simultaneous fitting of Equations 3
and 11, employing weighted least-squares regression analysis. The original
data came from Lorenz et al.83 Reprinted from Neafsey et al.,25 p. 140, by
permission of Marcel Dekker, Inc.