Chemical Exposures and Our Endocrine System
View count: 1234 Views

The endocrine system is the collection of glands that produce hormones that help regulate our metabolism, growth, development, tissue function, sexual function, reproduction, sleep and mood, among other things. The endocrine system is made up of the pituitary, thyroid, parathyroid and adrenal glands, as well as the pancreas, ovaries (in females) and testicles (in males).

The endocrine system is at work virtually all the time – and for good reason. Our bodies rely on hormones to manage many daily bodily functions, as well as ongoing bodily changes throughout our lives.

Given the importance of endocrine activity to human health, it’s understandable that the public may become concerned by the many articles on popular social media sites that claim exposures to some chemicals may “cause” lasting health impacts on the human endocrine system. Sometimes, these chemicals are referred to as EDCs, or “endocrine disrupting chemicals.”

How do we look beyond the headlines to understand what the science tells us? Some chemicals, both natural and man-made, can and do interact with the endocrine system. There is confusion as to whether this interaction is itself harmful, or if the endocrine activity could lead to harm above certain doses or at certain levels and frequencies of exposure.

Potency & Exposure

The interaction between chemicals and the endocrine system depends on the type and duration of the exposure to the chemical, the frequency of exposure, the potency of the substance and the way the body absorbs and eliminates a substance. Potency is a very important consideration when discussing potential endocrine disruptors. A simple analogy is the degree of burning sensation in the mouth that comes from eating various types of hot peppers. Some types, such as jalapenos and Habaneros, produce a more potent response that others, such as hot wax peppers.

It’s the interplay of these factors — exposure and potency — that can determine whether the endocrine system’s response is positive, neutral or negative.

Scientists have extensive knowledge, from decades of research on both natural and synthetic chemicals, about how various exposure levels can cause different effects. It is well established in scientific communities that while a particular substance can benefit people at the right dose, the same substance could cause a different response, including harm, at higher doses. This principle– of dose and response — applies to all chemicals, natural and synthetic, used in a variety of applications, such as cosmetics, personal care products, pharmaceuticals, crop protection and industrial manufacturing, among others.

How chemicals actually interact with the endocrine system depends on a variety of factors, such as how the chemicals are used, whether someone is actually exposed to the chemical, at what level and for how long. It’s the interplay of all of these factors that can determine whether the endocrine system’s response is positive, neutral or negative.

What do we mean by this? The following examples may provide some clarity:

  • Positive effect: Oral contraceptives, when taken correctly as prescribed by a doctor, enable family planning.
  • Neutral effect: Plant-based, naturally-occurring soy phytoestrogens, which are in milk and drinks such as soy lattes, can interact with the estrogen receptor to cause an endocrine response. Phytoestrogens are much less potent than estrogen produced by the body. While typical consumption of soy lattes may temporarily affect the endocrine system, there is no clinical evidence that such exposure would cause harm or have lasting effects.
  • Negative effect: At relatively high concentrations, the pesticide DDT is believed to have caused thinning in birds’ egg shells. Banned in the U.S. and Canada in the early 1970’s, levels of DDT in the environment have declined. With those decreased exposures, bird populations have largely recovered, and DDT is now used in a controlled, beneficial manner to kill mosquitos in tropical areas to combat malaria.

Endocrine Activity vs. Endocrine Disruptors

Many substances can interact with components of the endocrine system. But just because a substance interacts with the endocrine system, does not mean a negative effect will result. Those substances that go beyond a simple interaction and result in adverse health effects are called endocrine disruptors. An endocrine disruptor is a substance that directly alters the function of the endocrine system and consequently causes negative health impacts.

It is important to note that not all chemicals that interact with the endocrine system present a risk of harm – in many instances, the body naturally adjusts and there is no health effect. Just because a substance is endocrine active does not mean that it is endocrine disruptive.

Public interest around EDCs first emerged after the publication of the book by Theo Colborn and two others, Our Stolen Future, nearly 20 years ago. Since that time, the topic has continued to garner public interest, for scientific study and for government chemical policy discussions. Below, we explore both the science and the public policy developments around EDCs.

Global Policies & Perspectives on EDCs

It can be alarming to hear that chemicals may affect our endocrine or “hormonal system.” While scientific studies behind these issues can be quite complex, it is important from a consumer perspective to know what is being studied and what scientific organizations are doing to guide us with facts.

Identification of EDCs is a complex scientific and technical undertaking. Governments around the globe are analyzing how best to study and test for endocrine effects and determine if certain exposures to specific chemicals are cause for concern. The United States and several other countries are applying a science-based approach that considers both potential hazards of a chemical, as well as exposure and potency. In Europe, there is a discussion underway about adopting a categorization or list-based approach that only considers hazards to identify endocrine active chemicals. No consideration is given to the actual risk the chemical may or may not present.

United States: Risk-based Approach

In the United States, the Environmental Protection Agency (EPA) has established a science-based endocrine screening program that is focused on protecting public health and the environment. EPA is using high quality, validated test methods to determine which substances have the potential to interact with the endocrine system. Substances with such potential will then be further evaluated by EPA to determine whether adverse effects occur and what exposures trigger such responses. This testing typically includes exposures at levels far greater than what people would ordinarily be exposed to.

After this testing, chemicals that cause adverse effects will be subjected by EPA to a comprehensive risk assessment, so researchers can understand the potential for exposure to the chemical and the likelihood of harm under real-life scenarios. This science-based risk assessment helps scientists determine the “margins of safety”—the difference between the levels of exposure that produce adverse effects, and the typical exposure levels experienced by humans and wildlife. EPA would then decide if this margin of safety is appropriate to protect public health and the environment, including groups that might be particularly sensitive, or if limiting certain uses of the chemical should be considered.

Europe: Categorization Proposal

Currently, the European Union is considering a “categorization” or list-based approach that would identify endocrine active chemicals solely by their “hazard” – the possibility the chemical could cause harm. The approach has been criticized by many scientists as departing from well-established scientific principles. Rather than evaluate potencies, exposures and risk, like the EPA and other science-based programs, the EU is proposing to define and create two large categories: Category 1: “Known” endocrine disruptors, and Category 2: “Suspected” endocrine disruptors. While scientists may recognize the important distinction between “known” and “suspected” endocrine disruptors— that is, a “suspected” endocrine disruptor refers to a substance that has the potential to interact with the endocrine system, but which has not been shown to cause any adverse effects—others may not see this difference as clearly. To the general public, this nuanced distinction could likely create unnecessary confusion and alarm.

The approach the European Union is considering also does not take into account science-based considerations of potency or exposure. Meaning that, irrespective of how weakly a substance interacts with the endocrine system, or how minimal an exposure might be, if a chemical is put on either list, consumers could be alarmed by the mere presence of the chemical in the product. Such undue alarm could be triggered even if the science shows that the amount of the chemical used in a material or product is so miniscule that it could not possibly cause a negative health effect. The EU’s proposed approach goes beyond “an abundance of precaution,” to what is effectively a culture of suspicion that the mere presence of a chemical would cause harm.

Summary

Science will continue to evolve and be refined, as scientific and regulatory experts continue to examine and improve validated test methods for identifying endocrine disruptors and better understanding safe exposure levels.

The goal is for the science to enable regulators to reasonably assess real-life risk – the possibility of harm arising from a particular exposure to a specific chemical, under realistic conditions. In doing so, people can have a true understanding of their exposure to chemicals and what the actual health and environmental impacts are, so that they can make informed and confident decisions about the products and chemicals that are a part of their everyday lives.