16 BIOLOGICAL EFFECTS OF LOW LEVEL EXPOSURES
LONGEVITY HORMESIS: DISCUSSION OF THE
AUTHENTICATED DATA
Why then should I marvel or let myself be frightened because one part is
poison, and despise the other part too?... Now if the poison conquers not
but enters without harm when we use it according to nature’s ordered way,
why then should poison be despised? Who despises poison, knows not what is
in the poison. ... If you wish justly to explain each poison, what is there that
is not poison? All things are poison, and nothing is without poison: the Dosis
alone makes a thing not poison.
Paracelsus79
(1493-1541)Before discussing actual data, it would be helpful to examine simulations
based on an empirically useful Gompertz function, Equation 12. Superim
posed on a linear Gompertz function, this equation posits:
- a zero-order input of irreversible injury
- a zero-order input of longevity hormesis
- a first-order dissipation of retained longevity hormesis
To eliminate either toxicity or longevity hormesis, 7 or X is set equal to zero,
respectively. To account for dose-dependent effects, 7 and X may be
expressed as a function of dose (e.g., by utilizing the logarithmic-logistic
equation). Figure 1.2 illustrates a few of the possible curves that can be
Figure 1.2. Gompertz diagrams illustrating the effects of irreversible toxicity and/or
longevity hormesis on the linear Gompertz function. Curve C represents a
control population whose mortality experience is characterized by a linear
Gompertz function. Curve A assumes superimposition of only irreversible
toxicity; curve E assumes superimposition of only reversible longevity
hormesis; and curves B and D assume both irreversible toxicity and
reversible longevity hormesis simultaneously superimpose their effects on
the control function (toxicity is more dominant in B, i.e., a larger 7). Reprinted
from Neafsey et al.,24 p. 376, by permission of Marcel Dekker, Inc.