The endocrine system
The endocrine system is made up of a dozen or so glands, including the thyroid, pituitary, adrenal, thymus, pancreas, ovaries and testes, as well as pockets of tissue throughout the body, all of which secrete calibrated amounts of hormones into the blood stream. Hormones are chemical messengers that orchestrate many of the body’s internal functions — including cell growth, development and division — and how organs behave. They also handle communication between organs.
Hormone molecules or compounds travel around in the bloodstream to other target body parts with certain receptors on them. To use the best analogy we have for this at present, this mechanism is akin to traveling a hallway of many doors with a ring of keys in hand; each hormone molecule or compound acts as a key that will fit only certain locks. Once it chances upon a corresponding door and the lock is turned, the molecule and receptor complex sends a signal inside the cell to take or halt a certain action, such as to produce a certain protein or to multiply. The endocrine system is one of the three major networking systems in the body — the others being the nervous system with its electrical signals and the immune system with its antibodies.
Estrogen, progesterone, testosterone, DHEA, melatonin, insulin, cortisol, and the thyroid hormones are just a few of the primary and secondary hormones circulating in our bodies. (Click here to view a list of female endocrine glands and hormones.)
We now realize that all these hormones interact much more than originally thought. Highly evolved release, stimulating, and feedback mechanisms operate between all these molecules and their target organs as they circulate. We are also discovering that the hormone–receptor complexes are more intricate than originally thought and come in alternate forms (alpha and beta). This means that more keys can turn the lock than once imagined. While this all serves a valuable purpose in our bodies, it also makes endocrine disruption more potentially hazardous.
What are endocrine disruptors?
An endocrine disruptor is a synthetic compound that mimics a natural hormone when it is absorbed by the body. It can turn on, turn off, or change normal signals. It can have the effect of altering normal hormone levels, triggering excessive action, or completely blocking a natural response. Any other bodily function controlled by hormones can also be affected.
We are often asked about plant estrogens, “Aren’t they endocrine disruptors? Don’t they mimic estrogen?” Much research has shown that phytoestrogens, such as those found in soy, are not disruptive to the natural workings of the endocrine system. The reason behind this is that the human body has co-evolved over time with plants and generally moderates the impact of phytoestrogens through an adaptogenic response. Some plant estrogens are naturally neutralized, others are easily excreted, and most do not accumulate in body tissue (unlike synthetic compounds and heavy metals). The half-life of a phytoestrogen is measured in minutes, while the half-life of various synthetic compounds, like DDT, may be years or even decades.
Manmade chemicals that are known or suspected to influence the endocrine system are everywhere. All the latest and greatest, next-best-things that we now accept as “however-did-we-live-without-them” inventions are made with these chemicals. They make our plastic products softer and easier to handle, our cosmetic creams and lotions smoother and longer-lasting, and our clothes and furnishings inflammable. They are used in clothing dye (especially denim!), cars and computer casings, Teflon coatings, and disinfectant bleaches. They are diffused throughout the atmosphere by the burning of industrial waste and leach into groundwater from landfills. Scientists are concerned because these chemicals biomagnify in the food chain.
In humans, the natural level of circulating hormones needed to orchestrate bodily functions is relatively low. Synthetic endocrine disruptors are now being found in living tissue at dramatically higher concentrations than natural hormones. A CDC report from July 2005 found that the bodies of Americans of all ages contain an average of 148 synthetic chemicals.
Do these chemicals really have any effect, or are they inert? Why can’t the body neutralize manmade chemicals? The good news is, we probably can, but the pace at which new chemicals are being introduced is outdistancing our body’s ability to adapt. We have a rigorous detoxification system in place in the form of our blood, lymph, liver, kidneys, intestines, lungs, and skin. But we are moving very quickly with manmade chemicals — experts estimate that 40 million pounds of hormonally active chemicals are produced in this country per annum, with 2000 new varieties introduced to market each year. Even the healthiest person may have trouble filtering this kind of load.
There are many unanswered questions regarding the long-term effects of endocrine disruptors. Because they are a recent phenomenon, studies are just beginning to show possible connections. Research into the link between pesticides and frog deformities, fish sex reversals, and bird infertilities is well-documented. How this plays out further with mammals seems to be highly individualized, relative to variables such as age at exposure, genetics, level and length of exposure, gender, and detox capability. Some humans seem to be better at dealing with these substances, but we suspect that the increase in chemical and medical sensitivities, childhood cancers, infertility rates, learning disabilities, autism and mood disorders may relate in some way to the sea of endocrine disruptors in which we all swim.
The hopeful aspect here is that these hormonally active contaminants do not seem to alter most people’s basic genetic blueprint — although our understanding of DNA and protein changes is expanding daily. We understand that what one inherits can be molded, and that while a person cannot change his/her eye color, certain genes directing metabolism can be changed — for good or bad. It is all too soon to tell just what the next generation will inherit, but in looking back, we now realize that DES affected not only daughters but sons as well, and in more ways than just genital abnormalities. New evidence points to epigenetic possibilities, meaning that we can pass along certain effects without actually changing our offspring’s DNA. In addition, not all genes will be expressed under all conditions — that is, some effects may only get turned on generations from now, or only under certain circumstances.