Insulin, a hormone your pancreas secretes in response to rising blood glucose levels, is essential for human life. By helping the transfer of glucose from your bloodstream into your cells, insulin provides vital fuel for your cells' day-to-day functions. Without insulin, the glucose in your bloodstream would reach toxic levels, which is the situation that exists in people with poorly controlled diabetes. Insulin resistance -- a condition characterized by impaired cellular response to insulin -- is present in some people with diabetes, but it may also occur in people without diabetes.
The membranes of your cells are studded with receptors that are stimulated by insulin. These receptors are particularly active in muscle, liver and fat tissue, where glucose is avidly consumed. When insulin attaches to an insulin receptor, it initiates a complex cascade of reactions that end with the cell’s absorption of glucose. Insulin resistance occurs when your cellular receptors do not respond appropriately to the insulin you make. Insulin resistance has been identified in a number of disorders, most notably type 2 diabetes and prediabetes.
Type 2 Diabetes
Type 2 diabetes accounts for 90 to 95 percent of diabetes cases in American adults, and it is being diagnosed with increasing frequency in children and adolescents. According to a January 2011 review in “Diabetes Care,” insulin resistance is the driving force behind type 2 diabetes. Insulin production may be normal or elevated in people with type 2 diabetes, at least in the early stages of the disease. But because their cells do not respond to insulin, their blood glucose levels climb into the diabetic range. Overcoming insulin resistance -- which is worsened by obesity and inactivity -- is one of the keys to treatment for type 2 diabetes.
At least 1/3 of American adults have prediabetes, which means their blood glucose levels are higher than normal but not high enough to be diagnosed as diabetes, reports the Centers for Disease Control and Prevention. Prediabetes is a risk factor for type 2 diabetes and, like type 2 diabetes, is characterized by insulin resistance. Being overweight and leading a sedentary lifestyle increases your risk for prediabetes and type 2 diabetes. Studies show that weight loss and regular physical activity may prevent or delay the onset of type 2 diabetes. Many people who have prediabetes are not aware of their condition and don’t realize they need to alter their lifestyles. Your doctor can determine whether you have prediabetes.
Type 1 Diabetes
People with type 1 diabetes make too little or no insulin, rather than being insulin resistant. Type 1 diabetes is caused by immune destruction of your pancreatic beta cells, which are responsible for synthesizing and secreting insulin. By the time people with type 1 diabetes are diagnosed, up to 90 percent of their beta cells have been destroyed. So, type 1 diabetes is mainly managed through insulin replacement, rather than improving insulin sensitivity.
Insulin Resistance in Other Disorders
Several conditions are characterized by insulin resistance, including cardiovascular disease, obesity, fatty liver disease and cancer. While some of these disorders have been linked to type 2 diabetes, insulin resistance occurs in people who do not have diabetes. And not everyone with diabetes is insulin resistant. According to a 2012 review in “Journal of Biomedicine and Biotechnology,” the causes of insulin resistance in people with chronic diseases have not been clarified, but inflammation, altered energy metabolism and genetics may all play a role. Identifying the underpinnings of insulin resistance may eventually lead to new treatments for an array of medical conditions.