Endocrine disrupting chemicals (EDCs) are anything but simple. Hundreds of natural and synthetic substances are known to interfere with normal signaling that controls body processes. The direct or indirect meddling with hormone, brain, and energy signals produces a broad range of effects in organisms from bacteria to humans.

But, largely unknown are the precise actions of these substances that can have very different chemical shapes and structures than their natural signaling counterparts. A key to understanding the real health threats posed by EDCs is to untangle their mechanisms, or how they interfere with hormone production, function, and break down.

A Complex Reality

Normally, complex interactive systems of hormones, proteins, genes, and electronic signals relay messages within cells, between cells, and among organs and body systems. These intricate communication highways control every aspect of life: development, growth, behavior, maintenance, reproduction, and aging.

As few as one or as many as hundreds of steps, or interactions, convey these life-sustaining instructions. Interference at any juncture may alter the signal - and the message - and change the final outcome.

A growing body of research shows that EDCs can interfere in any number of places along the signaling routes, or pathways, that start and stop steroid and thyroid hormonal actions. They can act directly to initiate or block a signal or indirectly by influencing production, transport, and break down of hormones and other messengers.

More is known about how synthetic and plant chemicals interact with steroid hormone and thyroid hormone signals than with the other systems. Steroid hormones - including estrogens, androgens, progestins, glucocorticoids, and mineralocorticoids - control reproduction, metabolism, and ion balance in vertebrates. Thyroid hormones thyroxin and triiodothyronine are essential to lifetime growth, development, and tissue maintenance.

Less is understood about how EDCs may interfere with insulin and other peptide hormones, which help regulate metabolism, lactation, growth, and reproduction. Metals, such as cadmium and some organotin compounds, can affect peptide hormone levels resulting in abnormal signaling.

The most studied interactions involve the steroid hormones and thyroid hormones molecular “machinery” found in the bloodstream and in cells. EDCs influence many of these essential molecular components, including hormone receptors, hormone carrying proteins, signal relaying enzymes, and others.

One way EDCs interfere is by docking, or binding, to a hormone receptor and mimicking or blocking normal hormone responses.

Other ways are independent of the hormone receptor. Some compounds can alter hormone delivery by attaching to steroid or thyroid hormone transport proteins in the bloodstream and pushing off the natural hormone so that it never reaches its target.

Some EDCS change hormone production and disposal. Acting indirectly, they produce their effects by interrupting the elaborate enzyme relay systems inside cells. Or they can stimulate production of enzymes that change the natural balance of hormones, producing them too slowly or breaking them down too quickly.

Even though some EDC actions are known, factors such as age, gender, and hormone mixes make it difficult to predict human and animal health consequences. Understanding how disparate compounds interact with different parts of body signaling systems (dynamics) will be key to fully unlocking EDCs actions and effects.