Insulin
resistance is a silent condition that increases the chances of developing
diabetes and heart disease. Learning about insulin resistance is the first
step you can take toward making lifestyle changes that will help you prevent
diabetes and other health problems.
After you
eat, the food is broken down into glucose, the simple sugar that is the main
source of energy for the body's cells. But your cells cannot use glucose
without insulin, a hormone produced by the pancreas. Insulin helps the cells
take in glucose and convert it to energy. When the pancreas does not make
enough insulin or the body is unable to use the insulin that is present, the
cells cannot use glucose. Excess glucose builds up in the bloodstream,
setting the stage for diabetes.
Being
obese or overweight affects the way insulin works in your body. Extra fat
tissue can make your body resistant to the action of insulin, but exercise
helps insulin work well.
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If you
have insulin resistance, your muscle, fat, and liver cells do not use
insulin properly. The pancreas tries to keep up with the demand for insulin
by producing more. Eventually, the pancreas cannot keep up with the body's
need for insulin, and excess glucose builds up in the bloodstream. Many
people with insulin resistance have high levels of blood glucose and high
levels of insulin circulating in their blood at the same time.
People
with blood glucose levels that are higher than normal but not yet in the
diabetic range have "pre-diabetes." Doctors sometimes call this condition
impaired fasting glucose (IFG) or impaired glucose tolerance (IGT),
depending on the test used to diagnose it. In a cross-section of U.S. adults
aged 40 to 74 tested during the period 1988 to 1994, 33.8 percent had IFG,
15.4 percent had IGT, and 40.1 percent had pre-diabetes (IGT or IFG or
both). Applying these percentages to the 2000 U.S. population, about 35
million adults aged 40 to 74 would have IFG, 16 million would have IGT, and
41 million would have pre-diabetes.
If you
have pre-diabetes, you have a higher risk of developing type 2 diabetes,
formerly called adult-onset diabetes or noninsulin-dependent diabetes.
Studies have shown that most people with pre-diabetes go on to develop type
2 diabetes within 10 years, unless they lose 5 to 7 percent of their body
weight--which is about 10 to 15 pounds for someone who weighs 200 pounds--by
making modest changes in their diet and level of physical activity. People
with pre-diabetes also have a higher risk of heart disease.
Type 2
diabetes is sometimes defined as the form of diabetes that develops when the
body does not respond properly to insulin, as opposed to type 1 diabetes, in
which the pancreas makes no insulin at all. At first, the pancreas keeps up
with the added demand by producing more insulin. In time, however, it loses
the ability to secrete enough insulin in response to meals.
Insulin
resistance can also occur in people who have type 1 diabetes, especially if
they are overweight.
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Because
insulin resistance tends to run in families, we know that genes are partly
responsible. Excess weight also contributes to insulin resistance because
too much fat interferes with muscles' ability to use insulin. Lack of
exercise further reduces muscles' ability to use insulin.
Many
people with insulin resistance and high blood glucose have excess weight
around the waist, high LDL (bad) blood cholesterol levels, low HDL (good)
cholesterol levels, high levels of triglycerides (another fat in the blood),
and high blood pressure, all conditions that also put the heart at risk.
This combination of problems is referred to as the metabolic syndrome, or
the insulin resistance syndrome (formerly called Syndrome X).
|
Metabolic syndrome is defined by the National Cholesterol Education
Program as the presence of any three of the following conditions:
-
excess weight around the waist (waist measurement of more than
40 inches for men and more than 35 inches for women)
-
high levels of triglycerides (150 mg/dL or higher)
-
low levels of HDL, or "good," cholesterol (below 40 mg/dL for
men and below 50 mg/dL for women)
-
high blood pressure (130/85 mm Hg or higher)
-
high fasting blood glucose levels (110 mg/dL or higher)
Source:
National Cholesterol Education Program, Third Report of the Expert
Panel on Detection, Evaluation, and Treatment of High Blood
Cholesterol in Adults (Adult Treatment Panel III), National Heart,
Lung, and Blood Institute, National Institutes of Health, May 2001.
Note: Other definitions of
similar conditions have been developed by the World Health
Organization and the Association of Clinical Endocrinologists. |
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Insulin
resistance and pre-diabetes usually have no symptoms. You may have one or
both conditions for several years without noticing anything. If you have a
severe form of insulin resistance, you may get dark patches of skin, usually
on the back of your neck. Sometimes people get a dark ring around their
neck. Other possible sites for these dark patches include elbows, knees,
knuckles, and armpits. This condition is called acanthosis nigricans.
If you
have a mild or moderate form of insulin resistance, blood tests may show
normal or high blood glucose and high levels of insulin at the same time.
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Anyone 45
years or older should consider getting tested for diabetes. If you are
overweight and aged 45 or older, it is strongly recommended that you get
tested. You should consider getting tested if you are younger than 45,
overweight, and have one or more of the following risk factors:
-
family
history of diabetes
-
low HDL
cholesterol and high triglycerides
-
high
blood pressure
-
history
of gestational diabetes (diabetes during pregnancy) or gave birth to a
baby weighing more than 9 pounds
-
minority
group background (African American, American Indian, Hispanic
American/Latino, or Asian American/Pacific Islander)
Diabetes
and pre-diabetes can be detected with one of the following tests:
A
fasting glucose test measures your blood glucose after you have gone
overnight without eating. This test is most reliable when done in the
morning. Fasting glucose levels of 100 to 125 mg/dL are above normal but not
high enough to be called diabetes. This condition is called pre-diabetes or
impaired fasting glucose, and it suggests that you have probably had insulin
resistance for some time. IFG is considered a pre-diabetic state, meaning
that you are more likely to develop diabetes but do not have it yet.
A
glucose tolerance test measures your blood glucose after an overnight
fast and 2 hours after you drink a sweet liquid provided by the doctor or
laboratory. If your blood glucose falls between 140 and 199 mg/dL 2 hours
after drinking the liquid, your glucose tolerance is above normal but not
high enough for diabetes. This condition, also a form of pre-diabetes, is
called impaired glucose tolerance and, like IFG, it points toward a history
of insulin resistance and a risk for developing diabetes.
These
tests give only indirect evidence of insulin resistance. The test that most
accurately measures insulin resistance is too complicated and expensive to
use as a screening tool in most doctors' offices. The test, called the
euglycemic clamp, is a research tool that helps scientists learn more about
sugar metabolism problems. Insulin resistance can also be assessed with
measurement of fasting insulin. If conventional tests show that you have IFG
or IGT, your doctor may suggest changes in diet and exercise to reduce your
risk of developing diabetes.
If your
blood glucose is higher than normal but lower than the diabetes range, have
your blood glucose checked in 1 to 2 years.
Lab Tests and What They Show
-
Blood glucose.
High blood glucose may be a sign that your body does not have
enough insulin or does not use it well. However, a fasting
measurement or oral glucose tolerance test gives more precise
information.
-
Insulin.
An insulin measurement helps determine whether a high blood
glucose reading is the result of insufficient insulin or poor
use of insulin.
-
Fasting glucose.
Your blood glucose level should be lower after several hours
without eating. After an overnight fast, the normal level is
below 100 mg/dL. If it is in the 100 to 125 mg/dL range, you
have impaired fasting glucose or pre-diabetes. A result of 126
or higher, if confirmed on a repeat test, indicates diabetes.
-
Glucose tolerance.
Your blood glucose level will be higher after drinking a sugar
solution, but it should still be below 140 mg/dL 2 hours after
the drink. If it is higher than normal (in the 140 to 199 mg/dL
range) 2 hours after drinking the solution, you have IGT or
pre-diabetes, which is another strong indication that your body
has trouble using glucose. A level of 200 or higher, if
confirmed, means diabetes is already present.
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Yes.
Physical activity and weight loss make the body respond better to insulin.
By losing weight and being more physically active, you may avoid developing
type 2 diabetes. In fact, a major study has verified the benefits of healthy
lifestyle changes and weight loss. In 2001, the National Institutes of
Health completed the Diabetes Prevention Program (DPP), a clinical trial
designed to find the most effective ways of preventing type 2 diabetes in
overweight people with pre-diabetes. The researchers found that lifestyle
changes reduced the risk of diabetes by 58 percent. Also, many people with
pre-diabetes returned to normal blood glucose levels.
The main
goal in treating insulin resistance and pre-diabetes is to help your body
relearn to use insulin normally. You can do several things to help reach
this goal.
Physical
activity helps your muscle cells use blood glucose because they need it for
energy. Exercise makes those cells more sensitive to insulin.
The DPP
confirmed that people who follow a low-fat, low-calorie diet and who
increase activities such as walking briskly or riding a bike for 30 minutes,
five times a week, have a far smaller risk of developing diabetes than
people who do not exercise regularly. The DPP also reinforced the importance
of a low-calorie, low-fat diet. Following a low-calorie, low-fat diet can
provide two benefits. If you are overweight, one benefit is that limiting
your calorie and fat intake can help you lose weight. DPP participants who
lost weight were far less likely to develop diabetes than others in the
study who remained at an unhealthy weight. Increasing your activity and
following a low-calorie, low-fat diet can also improve your blood pressure
and cholesterol levels and has many other health benefits.
Scientists
have established some numbers to help people set goals that will reduce
their risk of developing glucose metabolism problems.
If you have
metabolic syndrome, your doctor may recommend weight loss with diet and
exercise, as well as medication to lower your cholesterol and blood pressure
levels.
In
addition to increasing your risk of cancer and cardiovascular disease,
smoking contributes to insulin resistance. Quitting smoking is not easy, but
it could be the single smartest thing you can do to improve your health. You
will reduce your risk for respiratory problems, lung cancer, and diabetes.
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Two
classes of drugs can improve response to insulin and are used by
prescription for type 2 diabetes--biguanides and thiazolidinediones. Other
medicines used for diabetes act by other mechanisms. Alpha-glucosidase
inhibitors restrict or delay the absorption of carbohydrates after eating,
resulting in a slower rise of blood glucose levels. Sulfonylureas and
meglitinides increase insulin production.
The DPP
showed that the diabetes drug metformin, a biguanide, reduced the risk of
diabetes in those with pre-diabetes but was much less successful than losing
weight and increasing activity. In another study, treatment with
troglitazone, a thiazolidinedione later withdrawn from the market following
reports of liver toxicity, delayed or prevented type 2 diabetes in Hispanic
women with a history of gestational diabetes. Acarbose, an alpha-glucosidase
inhibitor, has been effective in delaying development of type 2 diabetes.
Additional studies using other diabetes medicines and some types of blood
pressure medicines to prevent diabetes are under way. No drug has been
approved by the Food and Drug Administration (FDA) specifically for insulin
resistance or pre-diabetes.
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Researchers sponsored by the National Institute of Diabetes and Digestive
and Kidney Diseases conducted the DPP to find the most effective ways to
prevent or delay the onset of type 2 diabetes. Volunteers were recruited
from groups known to be at particularly high risk for IGT and type 2
diabetes. The study was designed to compare the effectiveness of lifestyle
changes (weight loss through exercise and diet) with drug therapy (metformin).
A control group received a placebo and information on diet and exercise.
Participants assigned to the intensive lifestyle intervention reduced their
risk of getting type 2 diabetes by 58 percent over 3 years. Participants
treated with metformin reduced their risk by 31 percent. Metformin is not
currently approved for use in preventing diabetes, but the FDA may determine
whether to make diabetes prevention an added indication for this drug. In
any event, the DPP demonstrates that a healthy diet and exercise are the
most effective treatment for insulin resistance and the prediabetic states
of IFG and IGT.
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-
Glucose
is the simple sugar that is the main source of energy for the body's
cells.
-
Insulin
helps cells take in blood glucose and convert it to energy.
-
If you
have insulin resistance, your body's cells do not respond well to
insulin.
-
Insulin
resistance is a stepping-stone to type 2 diabetes.
-
Lack of
exercise and excess weight contribute to insulin resistance.
-
Engaging
in moderate physical activity and maintaining proper weight can help
prevent insulin resistance.
-
Insulin
resistance plays a role in the development of cardiovascular disease,
which damages the heart and blood vessels.
-
Controlling blood pressure and LDL cholesterol and not smoking can also
help prevent cardiovascular problems.
-
The
Diabetes Prevention Program confirmed that exercise and a low-calorie,
low-fat diet are the best ways to prevent type 2 diabetes.
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National Diabetes Information Clearinghouse
1 Information Way
Bethesda, MD
20892-3570
Email:
ndic@info.niddk.nih.gov
The National Diabetes Information Clearinghouse (NDIC) is a service of the
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
The NIDDK is part of the National Institutes of Health under the U.S.
Department of Health and Human Services. Established in 1978, the
clearinghouse provides information about diabetes to people with diabetes
and to their families, health care professionals, and the public. NDIC
answers inquiries, develops and distributes publications, and works closely
with professional and patient organizations and Government agencies to
coordinate resources about diabetes.
Publications produced by the clearinghouse are carefully reviewed by both
NIDDK scientists and outside experts. This fact sheet was reviewed by George
A. Bray, M.D., Pennington Biomedical Research Center, Louisiana State
University; and Richard F. Hamman, M.D., Dr.P.H., Department of Preventive
Medicine and Biometrics, University of Colorado Health Sciences Center.
This e-text is not copyrighted. The clearinghouse encourages users of this
e-pub to duplicate and distribute as many copies as desired.
NIH
Publication No. 04-4893
May 2004
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