What is Insulin Resistance?
Cells throughout our body, such as muscle cells, require the hormone insulin to turn glucose into energy. Healthy working cells readily receive insulin, allowing the glucose to be used or stored as an energy source. Insulin resistance is an abnormal condition whereby the receptors of the cells that respond to insulin have lost sensitivity and become "resistant" to insulin. The root cause of insulin resistance lies at the cellular level with the islets, located in the pancreas, where insulin is produced. Insulin is available and circulating in the bloodstream, but the body's ability to use it is impaired.
Over time, people who are insulin resistant develop high levels of insulin in their body because their pancreas continues to pump out increasingly 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.
The majority of people with type 2 diabetes are insulin resistant. 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, as the ability of the pancreas to produce insulin becomes exhausted.
Weight loss, reduction of fatty foods in the diet, and increased physical activity help the cells respond better to insulin, and improve sensitivity to insulin.
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 sufficiently use injected insulin tto lower blood glucose levels. 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 between 100 and 125 mg/dl (6.1 and 7.1 mmol/l) or a two-hour glucose 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.
- Hemoglobin a1c level of 5.7-6.4%
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.
Reviewed by Zoe Heineman 01/14.
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