Estrogens are female sex hormones. Natural estrogens are responsible for female sexual development and play an essential role in fertility, pregnancy, and lactation. However, in both males and females excess estrogens can cause birth defects, abnormal sexual development, problems with the nervous system, the immune system, and cancer.
Many synthetic chemicals that also mimic estrogen are commercially manufactured for a specific purpose or produced as a byproduct, often as pharmaceuticals and contraceptives. The concern arises from the fact that, surprisingly, a number of synthetic chemicals (even some that do not closely resemble the structure of natural estrogens) have estrogen-like activity in animals, including humans. In some cases, these chemicals imitate estrogen in the body, but estrogen-like activity can also result from interference with the action or production of the natural hormones.
Environmental estrogens are the most studied of all the endocrine disruptors. The endocrine system is the network of glands and organs that maintain hormone balance. Natural compounds capable of producing estrogenic responses, such as the phytoestrogens, occur in a variety of plants and fungi, in addition to the synthetic chemicals that mimic estrogen.
Exposure to these substances occurs throughout our lives from food, air, water, soil, household products and probably through breast milk and during development in our mother's womb. The human health risks that may be associated with these low-level yet constant exposures are still largely unknown and highly controversial.
Some, called phytoestrogens, occur naturally in plants such as clover, soybeans and other legumes, whole grains and many fruits and vegetables. Others are synthetic chemicals made commercially for a specific purpose or produced as a byproduct of manufacturing processes.
Humans and other animals have a long history with phytoestrogens but a very short one with human-made environmental estrogens. Since the turn of the century, manufacture and use of synthetic chemicals has rapidly increased. So too has our exposure to them. These estrogenic chemicals, which differ from phytoestrogens in many ways, are found in:
Some scientists are concerned that average exposure to environmental levels of these kinds of chemicals may be sufficient to affect human health. However, some of these chemicals are used industrially. Workers in these industries are likely to have exposure to endocrine-disrupting chemicals at levels far greater than the average.
Several scientists at UC Davis' Center for Environmental Health Studies are currently examining the effects of environmental estrogens on reproduction, development, and overall health, since pesticide use is a major factor in the economy of California's central valley.
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