Insulin Resistance Health Article

Definition

Insulin resistance is a condition in which cells, particularly those of muscle, fat, and liver tissue, display "resistance" to insulin by failing to take up and utilize glucose for energy and metabolism (insulin normally promotes take up and utilization of blood glucose from the blood stream). In its early stages, the condition is asymptomatic, but may develop into Type II Diabetes. Although there are several established risk factors, the underlying cause is unknown.

It has been estimated that 30 to 33 million Americans are insulin resistant, and the number appears to be increasing.

Description

Insulin resistance is initially asymptomatic, and in its early stages can be detected only by laboratory tests. These tests will show an abnormally high blood sugar (glucose) level, but not high enough to be considered prediabetic or diabetic. While the condition does not always lead to further problems, the majority of people who reach the pre-diabetic level go on to develop Type II Diabetes (formerly called Maturity Onset Diabetes.

Causes & symptoms

The cause of insulin resistance is unknown, although the condition has been seen to run in families, indicating that there is a genetic association. Being overweight, and lack of exercise are also associated with insulin resistance, although the nature of the relationship is not clear. Risk factors for insulin resistance are:

• having a family history of diabetes
• having a low HDL (good) cholesterol level—and high serum lipids
• having high blood pressure
• having a history of diabetes during pregnancy, or having given birth to a baby weighing more than 9 pounds
• being a member of one of the racial groups that appear to have a high incidence of insulin resistance (African American, Native American, Hispanic American/Latino, or Asian American/Pacific Islander)
• having syndrome X
• being obese

In its mildest form, insulin resistance causes no symptoms, and is only recognizable on laboratory tests. In more severe cases, there may be dark patches on the back of the neck or even a dark ring around the neck. The dark patches are called Acanthosis nigricans and may also cause darkening of skin color in the elbows, knees, knuckles, and armpits.

There is a constellation of symptoms now called metabolic syndrome or insulin resistance syndrome that is linked to insulin resistance. This syndrome was 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 waistline (waist measurement of more than 40 inches for men and more than 35 inches for women)
• high levels of serum 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)

Note that the numbers are those from an expert panel convened by the National Institutes of Health in 2001. Other panels of similarly qualified experts have given slightly different definitions.

Diagnosis

The only means of diagnosis for insulin resistance is laboratory tests. While there are several tests that may be performed, the two most common screening tests are the fasting blood sugar test and glucose tolerance test.

Fasting blood sugar measures the blood glucose level after a 12-hour fast (no food). A normal level, according to the United Sates National Institute of Diabetes and Digestive and Kidney Disease (NIDDK), should be below 100 mg/dL (milligrams of glucose in every deciliter of blood. A value in the n the 100 to 125 mg/dL range is considered evidence of insulin resistance, and is considered prediabetic. A value of 126 mg/dL is considered diabetic. (Blood sugar levels after a 12 hr fast are typically lower than this, and are controlled by pancreatic insulin secretion that transports blood glucose out of the blood and into the muscles, brain, organs, and other tissues.)

The glucose tolerance test is performed after the patient has had nothing but water for 10 to 16 hours. The patient has his blood drawn for a a baseline blood glucose level. Next, the patient drinks a special sweetened test drink that contains exactly 75 grams of glucose (pregnant women are normally given 100 grams of glucose.) Blood is drawn again at one-half hour and each of the next six hours to compare blood glucose levels and watch their pattern in response to the sweet drink. Normally the blood sugar levels is lower before the drink, rises quickly during the first few hours, and slowly drops again. In insulin resistance, the blood sugar level rises but stays abnormally high because it is resistant to being removed from blood into tissues by insulin. High blood sugar from food or the test glucose drink stimulates the pancreas to secrete insulin into the blood. However, in insulin resistance, the insulin is secreted but is only partially absorbed by the tissues. According to the National Diabetes Information Clearinghouse (NDIC) a normal level would be below 140 mg/dL 2 hours after the drink. If it is in the 140 to 199 mg/dL range 2 hours after drinking the solution, the diagnosis is impaired glucose tolerance (IGT) or prediabetes. A level of 200 or higher, if confirmed, represents a diagnosis of diabetes.