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>From foodconsumer
http://www.foodconsumer.org/777/8/Pollutant_bisphenol-A_induces_insulin_resistance.shtml
Agri. & Environ.
Pollutant bisphenol-A induces insulin resistance
By David Liu Ph.D.
Sep 21, 2005, 00:46
Exposure to an extremely low dose of bisphenol-A (BPA) can disrupt the
pancreatic beta-cell function in vivo inducing insulin resistance,
according to a new study published in the Sept. 17-24 issue of
Environmental Health Perspectives.
BPA is a well known endocrine disruptor. Due to its cross-linking
properties, BPA was widely used by the chemical industry to produce
plastic polymers. These polymers were mainly polycarbonates, which are
often used to make transparent plastic bottles used to pack food and
beverages. BPA is also used to make barrier coasting for the inner
surface of food and beverage cans.
In previous studies, high concentrations of BPA have been detected in
food and water extracted from autoclaved cans. BPA is also found in 95
percent of the urine and blood samples from Americans.
Previous studies found that much lower doses of BPA than the lowest
adverse level (LOAEL) can affect sexual maturation, induce a decrease
in daily sperm count, fertility, disrupts chromosome alignment and
affects synaptogenesis.
In the study, researchers subcutaneously administered adult male mice
with an extremely low dose (10 ug/kg) of either 17beta-estradiol (E2)
or BPA, which was dissolved in tocopherol-stripped corn oil. The
concentration is over a thousand times lower than the minimal
concentration that the U.S. EPA believes has an adverse effect. E2 is a
natural hormone. Both BPA and E2 are similar in chemistry.
The researchers found that E2 or BPA induces a rapid decrease in
glycaemia that correlates with a rise of plasma insulin after two days
of treatment with 10 ug/kg/day of E2 or BPA. The pancreatic beta-cell
insulin content increased in an estrogen receptor-dependent manner.
After four days of treatment, the mice developed chronic
hyperinsulinaemia and their glucose and insulin tolerance were altered.
The researchers concluded that either abnormal levels of endogenous
estrogen or environmental estrogen enhance the risk of developing type
2 diabetes mellitus, hypertension and dyslipidaemia.
The toxicity of BPA has been officially recognized, but there is a
discrepancy among nations regarding the safe level of BPA. The European
Commission's Scientific Committee of Food reported a Tolerable Daily
Intake (TDI) of 10 ug/kg/day while the U.S. EPA considers 50 ug/kg/day
as the reference dose based on the LOAEL of 50 mg/kg/day.
The findings of the current study show that exposure to a concentration
of BPA 1000-times lower than the LOAEL used by the U.S. EPA can still
alter blood glucose homeostasis in vivo. It rapidly increases plasma
insulin altering blood glucose concentrations through a non-classical
estrogen pathway, according to the authors.
The study was funded by the Spanish Ministry of Education and Science
and Instituto de Salud Carlos III and conducted by Dr. Angel Nadal and
colleagues at Universidad Miguel Hernandez de Elche in Spain and
Instituto Nacional de Ciencias Medicas in Mexico.
© 2004-2005 by foodconsumer unless otherwise specified.
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