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 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)
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)
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.
Treatment
Among the most important treatment modalities are diet and exercise, weight loss if obese, endocrine hormone correction if unbalanced. In 2001, the National Institutes of Health completed the Diabetes Prevention Program (DPP), a clinical trial designed to find the most effective ways of preventing type 2 diabetes in overweight people with prediabetes. The researchers found that lifestyle changes reduced the risk of diabetes by 58 percent. Also, many people with prediabetes showed a return to normal blood glucose levels.
According to the DDP results, a mere half hour of brisk walking or bicycling five days a week can significantly reduce the risk of developing type 2 diabetes. Patients should use diet and exercise to reduce their body mass index (BMI) to 25 or below.
Smoking has been associated with insulin resistance, as well as with some of the more severe problems associated with diabetes. Discontinuing smoking should be a top priority.
A healthful diet, in addition to assisting in weight loss, may reduce serum lipids and reduce some of the risk factors for diabetes. One study recommended the Mediterranean diet as being the most beneficial for people with insulin resistance. Diet improvements include reducing sweets, desserts and high glycemic meals; eating balanced meals that contain protein, complex carbohydrates, fiber, greens and healthy oils, eating at regular times, and avoiding excess junk food and sugar.
No complimentary or alternative therapies have been proven to cure insulin resistance. Although several herbal remedies have been traditionally used for treatment of diabetes, none have been adequately documented as effective. Among medicinal plants shown to help lower elevated blood sugar are the Asian bitter melon and the Navaho Optunia cactus. Such herbal bitters as dandelion root and yellow dock can improve digestive strength and sometimes help, though no herbal remedy alone "cures" insulin resistance or diabetes. Guar gum, glucomannan, and psyllium seed all have demonstrated some ability to lower blood sugar in insulin resistance or diabetes, but none have been shown to be reliably effective for use in treatment of humans.
Allopathic treatment
Insulin resistance does not normally require drug therapy; however, some studies have shown that the drugs used to treat type 2 diabetes may delay development of diabetes. Two classes of drugs now used to treat diabetes act by increasing insulin sensitivity, the biguanides and the thiazolidinediones; the other drugs used to treat diabetes act in different ways.
Although drugs from both classes have been effective in treatment of insulin resistance, neither drug has been as effective as a regimen of diet and exercise. Both classes of drugs have the potential for very severe adverse effects. They are also not approved by the FDA for control of insulin resistance, although physicians may prescribe them for this use if the condition appears to be getting worse without drug therapy. In one study, oralhypoglycemic drugs of various mechanisms that help reduce elevated blood blood glucose reduced the rate of disease progression from insulin resistance to diabetes by about one-third over a three-year period.
Expected results
In mild asymptomatic insulin resistance, proper treatment may lead to a complete reversal, with normalization of blood sugar.
Even if complete normalization is impossible, treatment will lead to control of the condition, and a significant reduction in its rate of progression to diabetes.
Prevention
In insulin resistance, prevention is even better than treatment. Maintaining a normal weight, eating a balanced diet, and keeping up a regular program of aerobic exercise are the best preventive measures.
BOOKS
Beers, M. H., and R. Berkow, eds. The Merck Manual of Diagnosis and Therapy, 17th ed. Whitehouse Station, New Jersey: Merck and Co., 2004.
Blumenthal, M., ed. The Complete German Commission E Monographs. Austin, TX: American Botanical Council, 1999.
Blumenthal, M., ed. Herbal Medicine. Austin, TX: American Botanical Council, 2000.
Hart, C. R., and M. K. Grossman. The Insulin Resistance Diet. Chicago: Contemporary Books, 2001
PERIODICALS
Brame, L., S. Verma, T. Anderson, A. Lteif, and K. Mather. "Insulin resistance as a therapeutic target for improved endothelial function: metformin." Curr Drug Targets Cardiovasc Haematol Disord (March 2004): 53–63.
Camp, H. S. "Thiazolidinediones in diabetes: current status and future outlook." Curr Opin Investig Drugs (April 2003): 406–11.
Cargo, D. M. "Association between smoking, insulin resistance and beta-cell function in a North-Western First Nation." Diabet Med (February 2004): 188–93.
Dzien, A., C. Dzien-Bischinger, F. Hoppichler, and M. Lechleitner. "The metabolic syndrome as a link between smoking and cardiovascular disease." Diabetes Obes Metab (March 2004): 127–32.
Nelson, M. R. "Managing 'metabolic syndrome' and multiple risk factors." Aust Fam Physician (April 2004): 201–5. Osei, K, S. Rhinesmith, T. Gaillard, and D. Schuster. "Beneficial metabolic effects of chronic glipizide in obese African Americans with impaired glucose tolerance: implications for primary prevention of type 2 diabetes." Metabolism (April 2004): 414–22.
Scheen, J. "Current management strategies for coexisting diabetes mellitus and obesity." Drugs (2003): 1165–84.
Yamamoto, Y., I. Sogawa, A. Nishina, S. Saeki, N. Ichikawa, and S. Iibata. "Improved hypolipidemic effects of xanthan gum-galactomannan mixtures in rats." Biosci Biotechnol Biochem (October 2000): 2165–71.
ORGANIZATIONS
American Association of Clinical Endocrinologists (AACE). 1000 Riverside Avenue, Suite 205, Jacksonville, FL 32204.
National Organization for Rare Disorders. 55 Kenosia Avenue, PO Box 1968, Danbury, CT 06813-1968.
