Insulin Resistance and Prediabetes
On this page:
- What is insulin?
- What is insulin resistance?
- What happens with insulin resistance?
- What causes insulin resistance?
- Does sleep matter?
- What is prediabetes?
- How does insulin resistance relate to type 2 diabetes and prediabetes?
- What are the symptoms of insulin resistance and prediabetes?
- Who should be tested for prediabetes?
- Body Mass Index (BMI)
- What is metabolic syndrome?
- How are insulin resistance and prediabetes diagnosed?
- Understanding Test Results
- Can insulin resistance and prediabetes be reversed?
- What steps can help reverse insulin resistance and prediabetes?
- Eating, Diet, and Nutrition
- Points to Remember
- Hope through Research
- For More Information
What is insulin?
Insulin is a hormone made in the pancreas, an organ located behind the stomach. The pancreas contains clusters of cells called islets. Beta cells within the islets make insulin and release it into the blood.
Insulin plays a major role in metabolism—the way the body uses digested food for energy. The digestive tract breaks down carbohydrates—sugars and starches found in many foods—into glucose. Glucose is a form of sugar that enters the bloodstream. With the help of insulin, cells throughout the body absorb glucose and use it for energy.
Insulin’s Role in Blood Glucose Control
When blood glucose levels rise after a meal, the pancreas releases insulin into the blood. Insulin and glucose then travel in the blood to cells throughout the body.
- Insulin helps muscle, fat, and liver cells absorb glucose from the bloodstream, lowering blood glucose levels.
- Insulin stimulates the liver and muscle tissue to store excess glucose. The stored form of glucose is called glycogen.
- Insulin also lowers blood glucose levels by reducing glucose production in the liver.
In a healthy person, these functions allow blood glucose and insulin levels to remain in the normal range.
What is insulin resistance?
Insulin resistance is a condition in which the body produces insulin but does not use it effectively. When people have insulin resistance, glucose builds up in the blood instead of being absorbed by the cells, leading to type 2 diabetes or prediabetes.
Most people with insulin resistance don’t know they have it for many years—until they develop type 2 diabetes, a serious, lifelong disease. The good news is that if people learn they have insulin resistance early on, they can often prevent or delay diabetes by making changes to their lifestyle.
Insulin resistance can lead to a variety of serious health disorders. The section “What is metabolic syndrome?” provides more information about other health disorders linked to insulin resistance.
What happens with insulin resistance?
In insulin resistance, muscle, fat, and liver cells do not respond properly to insulin and thus cannot easily absorb glucose from the bloodstream. As a result, the body needs higher levels of insulin to help glucose enter cells.
The beta cells in the pancreas try to keep up with this increased demand for insulin by producing more. As long as the beta cells are able to produce enough insulin to overcome the insulin resistance, blood glucose levels stay in the healthy range.
Over time, insulin resistance can lead to type 2 diabetes and prediabetes because the beta cells fail to keep up with the body’s increased need for insulin. Without enough insulin, excess glucose builds up in the bloodstream, leading to diabetes, prediabetes, and other serious health disorders.
What causes insulin resistance?
Although the exact causes of insulin resistance are not completely understood, scientists think the major contributors to insulin resistance are excess weight and physical inactivity.
Some experts believe obesity, especially excess fat around the waist, is a primary cause of insulin resistance. Scientists used to think that fat tissue functioned solely as energy storage. However, studies have shown that belly fat produces hormones and other substances that can cause serious health problems such as insulin resistance, high blood pressure, imbalanced cholesterol, and cardiovascular disease (CVD).
Belly fat plays a part in developing chronic, or long-lasting, inflammation in the body. Chronic inflammation can damage the body over time, without any signs or symptoms. Scientists have found that complex interactions in fat tissue draw immune cells to the area and trigger low-level chronic inflammation. This inflammation can contribute to the development of insulin resistance, type 2 diabetes, and CVD. Studies show that losing the weight can reduce insulin resistance and prevent or delay type 2 diabetes.
Many studies have shown that physical inactivity is associated with insulin resistance, often leading to type 2 diabetes. In the body, more glucose is used by muscle than other tissues. Normally, active muscles burn their stored glucose for energy and refill their reserves with glucose taken from the bloodstream, keeping blood glucose levels in balance.
Studies show that after exercising, muscles become more sensitive to insulin, reversing insulin resistance and lowering blood glucose levels. Exercise also helps muscles absorb more glucose without the need for insulin. The more muscle a body has, the more glucose it can burn to control blood glucose levels.
Other causes of insulin resistance may include ethnicity; certain diseases; hormones; steroid use; some medications; older age; sleep problems, especially sleep apnea; and cigarette smoking.
What is prediabetes?
Prediabetes is a condition in which blood glucose or A1C levels—which reflect average blood glucose levels—are higher than normal but not high enough for a diagnosis of diabetes. Prediabetes is becoming more common in the United States. The U.S. Department of Health and Human Services estimates that at least 86 million U.S. adults ages 20 or older had prediabetes in 2012.1 People with prediabetes are at increased risk of developing type 2 diabetes and CVD, which can lead to heart attack or stroke.
How does insulin resistance relate to type 2 diabetes and prediabetes?
Insulin resistance increases the risk of developing type 2 diabetes and prediabetes. Prediabetes usually occurs in people who already have insulin resistance. Although insulin resistance alone does not cause type 2 diabetes, it often sets the stage for the disease by placing a high demand on the insulin-producing beta cells. In prediabetes, the beta cells can no longer produce enough insulin to overcome insulin resistance, causing blood glucose levels to rise above the normal range.
Once a person has prediabetes, continued loss of beta cell function usually leads to type 2 diabetes. People with type 2 diabetes have high blood glucose. Over time, high blood glucose damages nerves and blood vessels, leading to complications such as heart disease, stroke, blindness, kidney failure, and lower-limb amputations.
Studies have shown that most people with prediabetes develop type 2 diabetes within 10 years, unless they change their lifestyle. Lifestyle changes include losing 5 to 7 percent of their body weight—10 to 14 pounds for people who weigh 200 pounds—by making changes in their diet and level of physical activity.
What are the symptoms of insulin resistance and prediabetes?
Insulin resistance and prediabetes usually have no symptoms. People may have one or both conditions for several years without knowing they have them. Even without symptoms, health care providers can identify people at high risk by their physical characteristics, also known as risk factors. The section “Who should be tested for prediabetes?” lists these risk factors.
People with a severe form of insulin resistance may have dark patches of skin, usually on the back of the neck. Sometimes people have a dark ring around their neck. Dark patches may also appear on elbows, knees, knuckles, and armpits. This condition is called acanthosis nigricans.
Who should be tested for prediabetes?
The American Diabetes Association (ADA) recommends that testing to detect prediabetes be considered in adults who are overweight or obese and have one or more additional risk factors for diabetes. The section “Body Mass Index (BMI)” explains how to determine if a person is overweight or obese. However, not everyone who is overweight will get type 2 diabetes. People without these risk factors should begin testing at age 45.
Risk factors for prediabetes—in addition to being overweight or obese or being age 45 or older—include the following:
- being physically inactive
- having a parent or sibling with diabetes
- having a family background that is African American, Alaska Native, American Indian, Asian American, Hispanic/Latino, or Pacific Islander American
- giving birth to a baby weighing more than 9 pounds
- being diagnosed with gestational diabetes—diabetes that develops only during pregnancy
- having high blood pressure—140/90 mmHg or above—or being treated for high blood pressure
- HDL cholesterol level below 35 mg/dL or a triglyceride level above 250 mg/dL
- having polycystic ovary syndrome (PCOS)
- having prediabetes, impaired fasting glucose (IFG), or impaired glucose tolerance (IGT) on an earlier testing
- having other conditions associated with insulin resistance, such as obesity or acanthosis nigricans
- having CVD
If test results are normal, testing should be repeated at least every 3 years. Testing is important for early diagnosis. Catching prediabetes early gives people time to change their lifestyle and prevent type 2 diabetes and CVD. Health care providers may recommend more frequent testing depending on initial results and risk status.
In addition to weight, the location of excess fat on the body can be important. A waist measurement of 40 inches or more for men and 35 inches or more for women is linked to insulin resistance and increases a person’s risk for type 2 diabetes. This is true even if a person’s BMI falls within the normal range.
Body Mass Index (BMI)
Body mass index is a measurement of body weight relative to height. Adults ages 20 or older can follow the steps below using the BMI chart to find out whether they are normal weight, overweight, or obese:
- People should find their height in the left-hand column.
- They should move across the row to the number closest to their weight.
- Then, they should check the number at the top of that column.
The number at the top of the column is the BMI. The words above the BMI number indicate whether that person is normal weight, overweight, or obese. People who are overweight or obese should consider talking with a health care provider or registered dietitian about ways to lose weight to reduce the risk of diabetes.
The BMI chart has certain limitations. The chart may overestimate body fat in athletes and others who have a muscular build and underestimate body fat in older adults and others who have lost muscle. BMI for children and teens must be determined based on age and sex in addition to height and weight.
Information about BMI in children and teens, including a BMI calculator, is available from the Centers for Disease Control and Prevention (CDC) at www.cdc.gov/nccdphp/dnpa/bmi. The CDC website also has a BMI calculator for adults. A BMI calculator from the National Institutes of Health (NIH) is available at www.nhlbi.nih.gov/guidelines/obesity/BMI/bmicalc.htm.
The NIH also has a free smartphone app for calculating BMI. People can search “My BMI Calculator” on their phone to find the app. The app also provides links to information about steps people can take to bring their BMI into a healthy range.
Body Mass Index TablePrinter-friendly version (PDF, 70 KB) *
|Body Weight (pounds)|
|Body Weight (pounds)|
Source: Adapted from Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report, National Institutes of Health, 1998.
How are insulin resistance and prediabetes diagnosed?
Health care providers use blood tests to determine whether a person has prediabetes, but they do not usually test specifically for insulin resistance. Insulin resistance can be assessed by measuring the level of insulin in the blood.
However, the test that most accurately measures insulin resistance, called the euglycemic clamp, is too costly and complicated to be used in most health care providers’ offices. The clamp is a research tool used by scientists to learn more about glucose metabolism. Research has shown that if blood tests indicate prediabetes, insulin resistance most likely is present.
Blood Tests for Prediabetes
All blood tests involve drawing blood at a health care provider’s office or commercial facility and sending the sample to a lab for analysis. Lab analysis of blood is needed to ensure test results are accurate. Glucose measuring devices used in a health care provider’s office, such as finger-stick devices, are not accurate enough for diagnosis but may be used as a quick indicator of high blood glucose.
Prediabetes can be detected with one of the following blood tests:
- the A1C test
- the fasting plasma glucose (FPG) test
- the oral glucose tolerance test (OGTT)
A1C test. Sometimes called hemoglobin A1c, HbA1c, or glycohemoglobin test, this test reflects average blood glucose levels over the past 3 months. This test is the most reliable test for prediabetes, but it is not as sensitive as the other tests. In some individuals, it may miss prediabetes that could be caught by glucose tests.
Although some health care providers can quickly measure A1C in their office, that type of measurement—called a point-of-care test—is not considered reliable for diagnosis. For diagnosis of prediabetes, the A1C test should be analyzed in a laboratory using a method that is certified by the NGSP.
The A1C test can be unreliable for diagnosing prediabetes in people with certain conditions that are known to interfere with the results. Interference should be suspected when A1C results seem very different from the results of a blood glucose test. People of African, Mediterranean, or Southeast Asian descent, or people with family members with sickle cell anemia or a thalassemia, are particularly at risk of interference. People in these groups may have a less common type of hemoglobin, known as a hemoglobin variant, that can interfere with some A1C tests.
An A1C of 5.7 to 6.4 percent indicates prediabetes.
More information about the A1C test is available from the National Diabetes Information Clearinghouse (NDIC) fact sheet The A1C Test and Diabetes.
Fasting plasma glucose test. This test measures blood glucose in people who have not eaten anything for at least 8 hours. This test is most reliable when done in the morning. Prediabetes found with this test is called IFG.
Fasting glucose levels of 100 to 125 mg/dL indicate prediabetes.
OGTT. This test measures blood glucose after people have not eaten for at least 8 hours and 2 hours after they drink a sweet liquid provided by a health care provider or laboratory. Prediabetes found with this test is called IGT.
A blood glucose level between 140 and 199 mg/dL indicates prediabetes.
The following table lists the blood test levels for a diagnosis of prediabetes.
Understanding Test Results
A blood test indicating prediabetes means that insulin resistance has progressed to the point where the beta cells in the pancreas can no longer compensate and a person’s blood glucose levels are rising toward type 2 diabetes. The higher the test results, the greater the risk of type 2 diabetes. The level of risk also depends on an individual’s other risk factors, which are listed in the section "Who should be tested for prediabetes?"
Test numbers. For example, people with an A1C below 5.7 percent may still be at risk for diabetes if they have a family history of type 2 diabetes or have gained excess weight around the waist. People with an A1C above 6.0 percent should be considered at very high risk of developing diabetes. A level of 6.5 percent or above means a person has diabetes.
Follow up. People whose test results indicate they have prediabetes may be retested in 1 year and should consider making lifestyle changes to reduce their risk of developing type 2 diabetes.
Varying results. Although all these tests can be used to test for prediabetes, in some people one test will indicate a diagnosis of prediabetes or diabetes when another test does not. People with differing test results may be in an early stage of the disease, where blood glucose levels have not risen high enough to show on every test.
Health care providers repeat laboratory tests to confirm test results. Diabetes develops over time, so even with variations in test results, health care providers can tell when overall blood glucose levels are becoming too high.
Can insulin resistance and prediabetes be reversed?
Yes. Physical activity and weight loss help the body respond better to insulin. The Diabetes Prevention Program (DPP) was a federally funded study of 3,234 people at high risk for diabetes.
The DPP and other large studies proved that people with prediabetes can often prevent or delay diabetes if they lose a modest amount of weight by cutting fat and calorie intake and increasing physical activity—for example, walking 30 minutes a day, 5 days a week.
People at High Risk for Diabetes
DPP study participants were overweight and had prediabetes. Many had family members with type 2 diabetes. Prediabetes, obesity, and a family history of diabetes are strong risk factors for type 2 diabetes. About half of the DPP participants were from minority groups with high rates of diabetes, including African Americans, Alaska Natives, American Indians, Asian Americans, Hispanics/Latinos, and Pacific Islander Americans.
DPP participants also included others at high risk for developing type 2 diabetes, such as women with a history of gestational diabetes and people ages 60 and older.
Approaches to Preventing Diabetes
The DPP tested three approaches to preventing diabetes:
- Making lifestyle changes. People in the lifestyle change group exercised, usually by walking 5 days a week for about 30 minutes a day, and lowered their intake of fat and calories.
- Taking the diabetes medication metformin. Those who took metformin also received information about physical activity and diet.
- Receiving education about diabetes. The third group only received information about physical activity and diet and took a placebo—a pill without medication in it.
People in the lifestyle change group showed the best outcomes. However people who took metformin also benefited. The results showed that by losing an average of 15 pounds in the first year of the study, people in the lifestyle change group reduced their risk of developing type 2 diabetes by 58 percent over 3 years.
Lifestyle change was even more effective in those ages 60 and older. People in this group reduced their risk by 71 percent.
People in the metformin group also benefited, reducing their risk by 31 percent. More information about the DPP, funded under NIH clinical trial number NCT00004992, is available at www.bsc.gwu.edu/dpp.
The Diabetes Prevention Program Outcomes Study (DPPOS) has shown that the benefits of weight loss and metformin last for at least 10 years. The DPPOS has continued to follow most DPP participants since the DPP ended in 2001. The DPPOS showed that 10 years after enrolling in the DPP
- people in the lifestyle change group reduced their risk for developing diabetes by 34 percent
- those in the lifestyle change group ages 60 or older had even greater benefit, reducing their risk of developing diabetes by 49 percent
- participants in the lifestyle change group also had fewer heart and blood vessel disease risk factors, including lower blood pressure and triglyceride levels, even though they took fewer medications to control their heart disease risk
- those in the metformin group reduced their risk of developing diabetes by 18 percent
Even though controlling weight with lifestyle changes is challenging, it produces long-term health rewards by lowering the risk for type 2 diabetes, lowering blood glucose levels, and reducing other heart disease risk factors.
For more information about the risk of developing diabetes; the DPP, funded under NIH clinical trial number NCT00004992; and the DPPOS, funded under NIH clinical trial number NCT00038727, see the following NDIC publications:
- Diabetes Prevention Program
- Am I at risk for type 2 diabetes? Taking Steps to Lower Your Risk of Getting Diabetes
What steps can help reverse insulin resistance and prediabetes?
By losing weight and being more physically active, people can reverse insulin resistance and prediabetes, thus preventing or delaying type 2 diabetes. People can decrease their risk by
- eating a healthy diet and reaching and maintaining a healthy weight
- increasing physical activity
- not smoking
- taking medication
Eating, Diet, and Nutrition
Adopting healthy eating habits can help people lose a modest amount of weight and reverse insulin resistance. Experts encourage people to slowly adopt healthy eating habits that they can maintain, rather than trying extreme weight-loss solutions. People may need to get help from a dietitian or join a weight-loss program for support.
In general, people should lose weight by choosing healthy foods, controlling portions, eating less fat, and increasing physical activity. People are better able to lose weight and keep it off when they learn how to adapt their favorite foods to a healthy eating plan.
The DASH (Dietary Approaches to Stop Hypertension) eating plan, developed by the NIH, has been shown to be effective in decreasing insulin resistance when combined with weight loss and physical activity. More information on DASH is available at www.nhlbi.nih.gov/health/health-topics/topics/dash.
The U.S. Dietary Guidelines for Americans also offers healthy eating advice and tools for changing eating habits at www.choosemyplate.gov.
Vitamin D studies show a link between people’s ability to maintain healthy blood glucose levels and having enough vitamin D in their blood. However, studies to determine the proper vitamin D levels for preventing diabetes are ongoing; no special recommendations have been made about vitamin D levels or supplements for people with prediabetes.
Currently, the Institute of Medicine (IOM), the agency that recommends supplementation levels based on current science, provides the following guidelines for daily vitamin D intake:
- People ages 1 to 70 years may require 600 International Units (IUs).
- People ages 71 and older may require as much as 800 IUs.
The IOM also recommended that no more than 4,000 IUs of vitamin D be taken per day.
To help ensure coordinated and safe care, people should discuss use of complementary and alternative medicine practices, including the use of dietary supplements, with their health care provider.
More information about using dietary supplements to help with diabetes is available from the NDIC at www.diabetes.niddk.nih.gov/dm/pubs/alternativetherapies/index.aspx.
Regular physical activity tackles several risk factors at once. Regular physical activity helps the body use insulin properly.
Regular physical activity also helps a person
- lose weight
- control blood glucose levels
- control blood pressure
- control cholesterol levels
People in the DPP who were physically active for 30 minutes a day, 5 days a week, reduced their risk of type 2 diabetes. Many chose brisk walking as their physical activity.
Most people should aim for at least 30 minutes of exercise most days of the week. For best results, people should do both aerobic activities, which use large muscle groups and make the heart beat faster, and muscle strengthening activities.
Aerobic activities include brisk walking, climbing stairs, swimming, dancing, and other activities that increase the heart rate.
Muscle strengthening activities include lifting weights and doing sit-ups or push-ups.
People who haven’t been physically active recently should talk with their health care provider about which activities are best for them and have a checkup before starting an exercise program.
Those who smoke should quit. A health care provider can help people find ways to quit smoking. Studies show that people who get help have a better chance of quitting.
The medication metformin is recommended for treatment of some individuals at very high risk of developing type 2 diabetes. In the DPP, metformin was shown to be most effective in preventing or delaying the development of type 2 diabetes in younger, heavier people with prediabetes. In general, metformin is recommend for those who are younger than age 60 and have
- combined IGT and IFG
- A1C above 6 percent
- low HDL cholesterol
- elevated triglycerides
- a parent or sibling with diabetes
- a BMI of at least 35
Metformin also lowers the risk of diabetes in women who have had gestational diabetes. People at high risk should ask their health care provider if they should take metformin to prevent type 2 diabetes.
Several medications have been shown to reduce type 2 diabetes risk to varying degrees, but the only medication recommended by the ADA for type 2 diabetes prevention is metformin. Other medications that have delayed diabetes have side effects or haven’t shown long-lasting benefits. No medication, including metformin, is approved by the U.S. Food and Drug Administration to treat insulin resistance or prediabetes or to prevent type 2 diabetes.
Points to Remember
- Insulin is a hormone that helps cells throughout the body absorb glucose and use it for energy. Insulin resistance is a condition in which the body produces insulin but does not use it effectively.
- Insulin resistance increases the risk of developing type 2 diabetes and prediabetes.
- The major contributors to insulin resistance are excess weight, especially around the waist, and physical inactivity.
- Prediabetes is a condition in which blood glucose or A1C levels—which reflect average blood glucose levels—are higher than normal but not high enough for a diagnosis of diabetes.
- The Diabetes Prevention Program (DPP) study and its follow-up study, the Diabetes Prevention Program Outcomes Study (DPPOS), confirmed that people with prediabetes can often prevent or delay diabetes if they lose a modest amount of weight by cutting fat and calorie intake and increasing physical activity.
- By losing weight and being more physically active, people can reverse insulin resistance and prediabetes, thus preventing or delaying type 2 diabetes.
- People with insulin resistance and prediabetes can decrease their risk for diabetes by eating a healthy diet and reaching and maintaining a healthy weight, increasing physical activity, not smoking, and taking medication.
- The DPP showed the diabetes medication metformin to be most effective in preventing or delaying the development of type 2 diabetes in younger and heavier people with prediabetes and women who have had gestational diabetes.
Hope through Research
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) conducts and supports research in insulin resistance, diabetes, glucose metabolism, and related conditions. Clinical trials related to diabetes include
- Genetic Studies of Insulin and Diabetes, funded by the NIDDK under NIH clinical trial number NCT00001987
- Diabetes and Heart Disease Risk in Blacks, funded by the NIDDK under NIH clinical trial number NCT00001853
Clinical trials are research studies involving people. Clinical trials look at safe and effective new ways to prevent, detect, or treat disease. Researchers also use clinical trials to look at other aspects of care, such as improving the quality of life for people with chronic illnesses. To learn more about clinical trials, why they matter, and how to participate, visit the NIH Clinical Research Trials and You website at www.nih.gov/health/clinicaltrials. For information about current studies, visit www.ClinicalTrials.gov.
For more information about the NIDDK’s research on diabetes and related topics, see www.diabetes.niddk.nih.gov/diabetesresearch/dm_research.aspx.
For More Information
American Association of Diabetes Educators
200 West Madison Street, Suite 800
Chicago, IL 60606
National Heart, Lung, and Blood Institute Health Information Center
P.O. Box 30105
Bethesda, MD 20824–0105
Telecommunications Relay Services: 7-1-1
Publications produced by the Clearinghouse are carefully reviewed by both NIDDK scientists and outside experts. This publication was originally 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.
National Diabetes Education Program
The National Diabetes Education Program is a federally funded program sponsored by the U.S. Department of Health and Human Services’ National Institutes of Health and the Centers for Disease Control and Prevention and includes over 200 partners at the federal, state, and local levels, working together to reduce the morbidity and mortality associated with diabetes.
National Diabetes Information Clearinghouse
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 of 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. The NDIC answers inquiries, develops and distributes publications, and works closely with professional and patient organizations and Government agencies to coordinate resources about diabetes.
This publication is not copyrighted. The Clearinghouse encourages users of this publication to duplicate and distribute as many copies as desired.
NIH Publication No. 14–4893
Page last updated June 25, 2014