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Insulin Resistance & Estrogen
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Mar 31, 2011 | By Krithika Subramanian, Ph.D.
estradiole -
estrogen image by Cornelia Pithart from Fotolia.com
Insulin resistance is a condition in which the insulin produced
by the pancreas
becomes less effective at lowering blood sugar levels. It is a
defining feature ofmetabolic syndrome, along with obesity,
hypertension and dyslipidemia -- high
cholesterol and triglycerides. Insulin resistance is also a key
factor in the
development of type 2 diabetes and a risk factor for heart
disease. The female
hormone estrogen may play a role in protecting against insulin
resistance and
diabetes. Scientific studies are investigating the
estrogen-mediated regulation of
glucose levels.
Insulin Resistance Basics
Insulin is a hormone produced by beta-cells, a specialized kind
of cell in thepancreas. Insulin released from the beta-cells helps
other cells in the body take up
and utilize blood glucose, which is produced by the breakdown of
food by
digestion. In insulin resistance, muscle, liver and fat cells
fail to respond to the
insulin secreted by the beta-cells. The body needs higher
amounts of insulin in
order to take up and use glucose. Persistent insulin resistance,
marked by high
levels of glucose and insulin in the blood, eventually leads to
diabetes. Obesity,
high blood pressure and abnormal cholesterol levels often
coexist with insulin
resistance to result in a condition called metabolic
syndrome.
Risk factors for developing insulin resistance include obesity
-- a body mass index
above 25; excess weight, especially around the waist or an
"apple shape; having a
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parent or sibling with diabetes; physical inactivity; and in
women, having
polycystic ovarian syndrome or PCOS.
Treatment and Prevention
Extensive lifestyle modification -- by increasing physical
activity and maintaining
a healthy weight -- is the first recommendation for patients
with insulin resistance.
Many drugs are used to treat insulin resistance and type 2
diabetes, if present, and
other features of metabolic syndrome. However, according to the
American
Diabetes Association, Metformin is the only drug to be
considered for preventing
development of insulin resistance into diabetes.
Effects of Estrogen
Estrogen is a steroid hormone produced primarily in the ovaries,
and to a much
lesser extent in other cells, like fat tissue. Small amounts of
estrogen are also
produced in men. Estrogen production from the ovaries declines
around and after
menopause. The decrease in insulin sensitivity with menopause
suggests that
estrogen generally protects against insulin resistance in women.
Moreover, loss of
estrogen function, through changes in estrogen receptor, has
been shown to cause
insulin resistance and type 2 diabetes in a male patient.
Further evidence for the role of estrogen in glucose regulation
comes from studies
in lab-grown cells and animal models of human disease. Mice
deficient in
estrogen receptor -- a protein that binds estrogen within cells
-- become obese and
insulin resistant. Ablation of estrogen by removal of ovaries in
animal models
impairs insulin sensitivity. This effect, however, could be
reversed upon
supplementation with estrogen. Estrogen receptor also improves
the survival and
glucose-stimulated insulin synthesis of pancreatic
beta-cells.
Mechanism of action
Estrogen acts directly on beta-cells to make them resistant to
apoptosis -- a kind of
cell death-- and increase insulin production. This mechanism is
thought to assist
the pancreatic cells to adapt to higher insulin demands
associated with someconditions, like pregnancy and obesity. However
inappropriate estrogen function,
due to abnormal increases in estrogen or stimulation with
estrogen-mimics like
bisphenol-A, can actually provoke insulin resistance by
exhausting beta-cells
through overstimulation.
Estrogen has also been reported to have anti-inflammatory
properties. For
instance, a study published in 2002 in "Endocrine Reviews" found
that a decrease
in estrogen after menopause was associated with increased
pro-inflammatory
cytokines -- small proteins that amplify inflammatory response
of the immune
system. Increases in inflammatory molecules are associated with
obesity-induced
insulin resistance. These are some mechanisms by which estrogen
provides
