Broad trends in scientific findings about endocrine disruption

Endocrine disruption burst onto the public and policy scene in the mid-1990s, propelled by a growing body of science and then galvanized by the publication of Our Stolen Future. For a good history of this dynamic, read Sheldon Krimsky's 1999 book, Hormonal Chaos.

Since publication of Our Stolen Future, the emerging science has emphasized 6 broad trends:

1. Exposure is ubiquitous. All humans have been exposed, to varying amounts. Some have more exposure. Some have less. But no one has no exposure. No baby has been born for at least three decades without some exposure in the womb. Every person has several hundred novel chemicals in their body, chemicals not part of human body chemistry before the 20th century.
2. Laboratory experiments show that exposures have impacts at levels far lower than had been considered possible in traditional toxicology. The exquisite sensitivity of natural hormonal control to interference by endocrine disruptors will force many changes in regulations, as the current system is inadequate.
3. Many more hormone systems, perhaps all chemically-mediated message systems, are now known to be vulnerable to endocrine disruptors. The study of endocrine disruption began with a focus on compounds capable of mimicking or interfering with estrogen. Now science has revealed disruptors for almost every hormone system that has been studied. This includes other sex steroid hormones, like testosterone and progesterone, as well as thyroid and retinoids.
4. Many more compounds are now known to be powerful endocrine disruptors. This includes contemporary use pesticides and a range of chemicals in widespread use in consumer products. The biggest surprise (except, perhaps, to the polymer chemists who invented them) is that certain plastics show endocrine-disrupting effects.
5. Human health effects of concern now include adult impacts of fetal exposure. This means, for example, that studies attempting to prove an association between adult levels of exposure and adult risk to disease or dysfunction do not test the most important potential links between endocrine disruptors and human health. We need studies of developmental exposure (especially fetal) in relation to risk, examined for all relevant life stages. For example, one of the greatest gaps in breast cancer research is that while many studies examine adult exposure and adult risk, none examine fetal or pubertal exposure and adult risk.
6. Human epidemiology is biased toward false negatives in the search for health effects of endocrine disruption. It will be exceedingly difficult, if not impossible, to establish scientific certainty of causation of many health problems in human, even though based on laboratory data it is likely that endocrine disruption is involved in a range of human diseases. Because the animal data demonstrate plausible, serious risks to human healths, this bias toward false negatives (a statistical term that means finding no association when in fact there is one) requires the application of the precautionary principle, using animal data as the guide.

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