The nutrient-toxin dosage continuum in human evolution and modern health

Recent findings support the long-recognized Principle that nutritive and to xic effects of an an ingested material depend not only on its nature but ve ry much on its quantity. The well known observation that essential nutrient s can be toxic at high dosages suggests that the same reversal of effect ma y be true of many substances that could be beneficial but not essential at low dosages (the phenomenon of hormesis). This has been demonstrated for ma ny well known toxins. We suggest a mathematical model that describes these dosage effects as an expected result of the evolution of human metabolic an d dietary adaptations for maximizing benefits and minimizing costs of the i ngestion or other intake of any substance Evolved mechanisms for achieving benefits may be unrelated to those for reducing costs. These evolutionary c onsiderations suggest important consequences demonstrable by experimental o r epidemiological studies. They also suggest ways in which our evolved diet ary adaptations may be currently maladaptive, and individual development of taste preferences poorly calibrated by early experience in modern environm ents. The apparent reality of hormesis raises the possibility of counterpro ductive effects of current dosage recomendations and limits for nutrients a nd pollutants. We propose that some conceptual and factual problems are urg ently in need of resolution. Fundamental to evolutionary biology is the tendency for organisms to become increasingly adapted to those environments to which they are most commonly exposed (Parsons 1990). The theory of natural selection has always had a close affinity with econom ic principles (Frank 1999).