What is Insulin Resistance?
Insulin resistance is a condition characterized by an inability of the body to utilize the hormone insulin properly. Insulin, produced by the beta cells of the pancreas, is responsible for 'unlocking' cells to let glucose inside to be metabolized for energy. If their are too few insulin receptors (i.e., the cell 'lock' where insulin binds), or if the insulin receptors don't respond as they should, insulin resistance is the result.
The majority of people with type 2 diabetes are insulin resistant. They have plenty of insulin, but their bodies do not process it correctly. People with type 1 diabetes may also have some degree of insulin resistance, but are primarily insulin insufficient (i.e., their pancreas produces little to no insulin). Some people with type 2 diabetes may also develop insufficiency along with insulin resistance over time.
People who are insulin resistant have high levels of circulating insulin (i.e., hyperinsulinemia) in the body. This is because their pancreas continues to pump out more and more insulin in an effort to lower rising blood glucose levels. When an individual can no longer produce enough insulin to compensate for the rise, type 2 diabetes develops.
History of Insulin Resistance
Insulin resistance is not a new phenomenon, although media attention to rising rates of obesity and prediabetes in recent years has certainly raised awareness of the condition. It was first associated with diabetes in the 1930s by British physician Harold Percival Himsworth, who coined the term "insulin insensitivity" to describe patients who were unable to effectively use injected insulin to lower blood glucose levels sufficiently. Himsworth's work was the first to acknowledge the existence of two distinctly different types of diabetes.
Fifty years and much research later, Dr. Gerald Reaven described metabolic syndrome X - a condition of insulin resistance, high insulin levels, high triglycerides, and low HDL (good) cholesterol that raises both type 2 diabetes and heart disease risk.
Making the Diagnosis
An estimated one in three Americans is insulin resistant, a condition that puts them at high risk for developing type 2 diabetes and cardiovascular disease. A physician will diagnose insulin resistance based on medical history, risk factors, and lab tests.
The following lab results suggest a diagnosis of insulin resistance syndrome:
- A fasting glucose level (link to newly created page under type 1 diagnosis; blood tests) between 110 and 125 mg/dl (6.1 and 7.1 mmol/l) or a two-hour glucose (link to newly created page under type 1 diagnosis; blood tests) postload (75 g) level of 140 to 199 mg/dl (7.8 and 11.1 mmol/l). Triglycerides of 150 mg/dl or higher.
- HDL cholesterol of < 40 (men) or < 50 (women).
- Blood pressure of 130/85 mmHg or higher.
The presence of other risk factors can also help your doctor determine if you are insulin resistant.
Risk Factors for Insulin Resistance
The American Association of Clinical Endocrinologists (AACE) cites the following risk factors for insulin resistance syndrome:
- Being overweight or obese.
- Leading a sedentary lifestyle.
- Being over age 40.
- Being in one of the following ethnic groups: Latino or Hispanic American, African American, Native American, Asian American, Pacific Islander.
- A history of glucose intolerance or gestational diabetes.
- Existing type 2, hypertension, or cardiovascular disease.
- Elevated triglycerides/low HDL-cholesterol.
- Acanthosis nigricans. This skin condition is characterized by dark, velvety patches caused by insulin build up.
- Polycystic ovary syndrome. An estimated one in ten women have PCOS.
- Nonalcoholic fatty liver disease.
1 - American Association of Clinical Endocrinologists. American College of Endocrinology Position Statement on the Insulin Resistance Syndrome. (PDF accessed 2/15/08).
2 - American Association of Clinical Endocrinologists. The Insulin Resistance Syndrome and Obesity Fact Sheet, www.aace.com/meetings/consensus/irscc/irsfs.php (Accessed 2/15/08).
3 - WomensHealth.gov. Polycystic Ovary Syndrome (PCOS), www.forwomen.gov/faq/pcos.htm#b. (Accessed 2/15/08).
Reviewed by Francine Kaufman, M.D., 04/08
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