There is great interest in the seventy-five phenoxy acid compounds which constitute the group labeled
dioxins (polychlorinated dibenzo-p-dioxins). The most acutely toxic of the polychlorinated dibenzo-p-dioxin isomers is considered to be 2,3,7,8-
tetrachlorodibenzo-p-dioxin, hereafter TCDD. Since dioxin is found in trace amounts in some herbicides, autoexhaust, and the incineration
process, humans could be exposed to it just by eating meat, fish, eggs or diary products. While declared a human carcinogen by both the International Agency for Research on Cancer (IARC) and the United States Environmental Agency (EPA), a critical review of these declarations
has concluded that “the long-term accumulation of negative, weak, and inconsistent findings suggests that TCDD eventually will be recognized
as not carcinogenic for humans (italics mine)” (Cole et al. 2003).
Epidemiological and other studies
support the protective role of fruits and vegetables against cancer, including
prospective epidemiological studies of atomic bomb radiation survivors
(Hayes 2005). Hormesis has been suggested to explain the paradox
that plant foods containing carcinogens also protect against cancer with
the plant diet bringing together many different toxic chemicals that when
ingested at low doses stimulate the chemo-defense system and enhance
host resistance (Parsons 2000; Rico 2002). There is also evidence that
some synthetic chemical pesticides that enhance tumor formation at high
doses may affect a reduction in tumor incidence at lower doses. For example,
biphasic dose-responses have been reported in DDT laboratory rat
studies (Sukata et al. 2002; Kushida et al. 2005).
Evidence for nutritional hormesis arising from essential nutrients (vitamins and minerals), dietary pesticides (natural and synthetic), dioxin and other herbicides, and acrylamide have been reviewed and discussed. The evidence is an operational definition of Paracelsus’ dictum that the efficacy of toxic chemicals depends on dosage which in no ways negates the historic misuse and dangers of many of these things. Nutritional hormesis could very well be applicable as a pro-health intervention by extending human healthspan. An example of this arises from the hormetic agent vitamin D which has been posited to play a productive and positive role by reducing susceptibility in the elderly to various chronic degenerative diseases (Hayes 2009).