Xenoestrogen
From Wikipedia, the free encyclopedia
Xenoestrogens are novel, man-made compounds, that differ from archiestrogens (ancient, naturally occurring) produced by living organisms. They mimic the effect of other estrogens. Their potential ecological and human health impact is under study.[1]
Xenoestrogens are part of a heterogeneous group of chemicals that are hormonally active agents. They differ from phytoestrogens (estrogenic substances from plants), mycoestrogens (estrogenic substances from fungi, which can be considered as one type of mycotoxin), and pharmacological estrogens (estrogenic action is intended) in that they are man-made and their effects are unintended. Estrogens from a variety of sources may have a cumulative effect upon living organisms, and xenoestrogens may be part of a larger picture of a process of estrogenisation of the environment. Xenoestrogens have been introduced into the environment by industrial, agricultural and chemical companies in only the last 70 years or so, but similar compounds have existed in the environment since the beginnings of life itself. (see phytoestrogens)
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[edit] Effects
Xenoestrogens have been implicated in a variety of medical problems, but there is little hard evidence that they actually cause any adverse effects in humans[2]. Foremost is the concern that xenoestrogens as false messengers disrupt the process of reproduction. Xenoestrogens have an effect similar to that of naturally produced estrogen and can increase growth of the endometrium, so treatments for endometriosis include avoidance of products which contain them. Likewise, they are avoided in order to prevent the onset or aggravation of adenomyosis. Studies have implicated observations of disturbances in wildlife with estrogenic exposure. Reproductive issues which are of concerns in humans are fetal exposure (perhaps leading to hypospadias) and decreased reproductive ability in men (i.e. decrease in sperm numbers).
In a study by Sharpe and Shakkeback, published in the respected scientific journal, The Lancet in 1993, the researchers attributed the incidence of falling sperm counts in males to increased oestrogen exposure in utero.
Another issue is the potential effect of xenoestrogens on oncogenes, specifically in relation to breast cancer. Some scientists doubt that xenoestrogens have any significant biological effect, in the concentrations found in the environment.[3]
[edit] Presence
The ubiquitous presence of such estrogenic substances is a significant health concern, both individually and for a population. Life relies on the transmission of biochemical information to the next generation, and the presence of xenoestrogens may interfere with this transgenerational information process through "chemical confusion" (Vidaeff and Sever)[4], who state: "The results do not support with certainty the view that environmental estrogens contribute to an increase in male reproductive disorders". Agencies such as the United States Environmental Protection Agency and the World Health Organization International Programme on Chemical Safety are charged to address these issues.
[edit] Research
Believers that environmental estrogen disruption is a major health hazard are opposed by detractors who argue that observed effects are spurious and inconsistent, or that the quantities of the agents are too low to have any effect.[5]
A 2005 study by Belcher and coworkers demonstrated that even very low levels of a xenoestrogen, in this case Bisphenol A, could affect fetal neural signalling more than higher levels (PMID 16123166), indicating that classical models where dose equals response may not be applicable in susceptible tissue. As this study involved intra-cerebellar injections, its relevance to environmental exposures is unclear.
