Based on a report by Michael A. Kamrin, Ph.D.
Executive Summary
- It has been claimed that low doses of hormonally active substances in the environment may cause health problems that do not occur in response to higher doses. This allegation is highly controversial.
- Between 2000 and 2002, expert panels in the United States and Europe critically evaluated the evidence available at that time for low dose effects of bisphenol A, the most studied compound. The panels concluded that a low dose effect on reproduction or development had not been conclusively established and noted that the findings of different studies had not been consistent.
- Substantial additional research has been completed since the expert panels evaluated the low dose hypothesis. However, the validity of the newer research on low dose effects is as uncertain as the validity of the earlier studies. The general conclusions reached in earlier evaluations remain valid. The studies that have been alleged to support the low dose hypothesis cannot be validly extrapolated to the human situation; the effects observed in these studies are inconsistent and not necessarily harmful; and the doses at which the studies have been performed are higher than the doses to which people are customarily exposed.
- Careful assessment of all of the available data, including both animal and human evidence, indicates that the low dose hypothesis remains unproven. There is no compelling evidence that people are being put at risk by current levels of exposure to bisphenol A or other substances alleged to be “endocrine disruptors.”
Concerns were raised during the late 1990s about the possibility that hormonally active substances in the environment may cause health problems when present in low doses. It has been alleged that these so-called “low dose” effects cannot be detected using traditional toxicology studies, which involve the administration of high doses of test substances to experimental animals. This idea, called the low dose hypothesis, is highly controversial. In this report, the American Council on Science and Health evaluates the scientific evidence pertaining to the low dose hypothesis, including recent studies that were completed after expert panels evaluated the evidence on this topic several years ago. The principal source for this report is a technical review by Michael A. Kamrin, Ph.D., of Michigan State University, which will be published in the International Journal of Toxicology.
Introduction
During the early 1990s, it was alleged that reproductive and developmental problems in wildlife might be linked to hormonally active synthetic compounds in the environment. Concerns were raised that similar effects might occur in people. However, formal scientific studies did not show any link between environmental agents and the suspected adverse effects.
By the late 1990s, the nature of the concerns had shifted. Claims were made that the hormonally active compounds were indeed causing harmful effects at low doses but that these effects had not been detected in earlier research because they occur only at low doses, not at high ones, and therefore would not be observed in conventional high dose toxicology studies. It was also asserted that the low doses at which effects occur in experimental animals are similar to the doses to which people are commonly exposed, indicating that the human population is at risk.
Much of the research on alleged low dose effects has focused on bisphenol A, a substance used in the manufacture of many consumer products, including some types of plastic bottles. Very small amounts of bisphenol A may migrate into foods and beverages from plastic containers, thereby exposing people to low doses of this substance. Critics of bisphenol A claim that it is an “endocrine disruptor,” meaning that low doses might interfere with the normal functioning of body hormones, with resulting adverse effects on reproduction and development.
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