Insulin resistance

Insulin resistance is important to recognize and treat because it can lead to prediabetes and diabetes. Some dangerous complications of diabetes are increased risk of stroke and heart attack, blindness, and kidney disease.

Definition & Facts

Insulin is a hormone that is made by the pancreas and secreted after eating when blood sugar levels rise following the breakdown of food. Insulin attaches to cells and signals them to admit blood sugar (glucose) from the bloodstream so that the cells can use the glucose for energy.

If the cells are resistant to insulin, blood sugar cannot enter the cells, and glucose accumulates in the bloodstream at excessive levels (hyperglycemia). The pancreas then produces excessive amounts of insulin (hyperinsulinemia) in order for the cells to absorb glucose. Eventually, the pancreas isn't able to produce enough insulin to keep up with the cells' demands, and glucose accumulates in the bloodstream, causing diabetes.

Exactly why the cells become resistant to insulin is unknown though it is strongly believed to relate to leading a sedentary lifestyle and obesity.

Symptoms & Complaints

Extremely high levels of insulin can cause dark, velvety patches of skin called acanthosis nigricans. These areas of skin may be thickened and most frequently occur on the armpits, groin, and on the back of the neck. Since insulin resistance involves cells being unable to properly use energy, many individuals with this condition tend to eat more in an attempt to better fuel cells. This increased caloric intake often leads to weight gain.

Increased insulin levels change cholesterol in ways that have been linked to increased risk of cardiovascular disease, raising triglycerides and lowering HDL or “good” cholesterol, as well as increasing the amount of fat that accumulates around the heart, liver, and other organs.

Excess insulin can also damage the cardiovascular system because it has been linked to kidney damage that causes high blood pressure as well as systemic inflammation. 

Causes

Insulin creation, secretion, attachment and signaling to cells are such distinct and complex processes that researchers do not yet have a definitive cause or set of causes for insulin resistance. Although some genetic disorders have been linked to insulin resistance, researchers point to eating and lifestyle habits to identify risk factors.

Many individuals who have this condition tend to carry excess weight around the abdomen or belly fat. In addition to increasing the risk of insulin resistance, this excessive amount of belly fat can indicate a higher risk of prediabetes and diabetes.

Even though excess abdominal fat often reflects long-term lifestyle choices such as a high-fat diet or sedentary lifestyle, normal weight or thin individuals can have insulin resistance and all of its increased risks to health. Vitamin D deficiency can also lead to insulin resistance because vitamin D is needed to make cells sensitive to insulin. 

Diagnosis & Tests

Insulin resistance is typically not tested by itself. Healthcare providers usually perform tests for prediabetes and diabetes, which are possible proof of insulin resistance. These tests include the fasting glucose test, A1C (glycated hemoglobin) test and the oral glucose tolerance test.

The fasting glucose test is a blood test that measures the level of blood sugar after fasting for at least eight hours. A normal result is a level lower than 100 mg/dL, a prediabetic level is between 100 and 125 mg/dL and a diabetic result is 126 mg/dL or greater.

The A1C test is a blood test that measures the average blood sugar levels over the past ninety days. A normal A1C is about 5, a prediabetic one is between 5.7 and 6.4, and a diabetic A1C is 6.5 or above. An oral glucose tolerance test is performed after an 8-hour fast is followed by drinking a glucose solution. Blood is drawn two hours after drinking the glucose. A normal result on this test is lower than 139 mg/dL, a prediabetic level is 140 to 199 mg/dL and a diabetic level is 200 mg/dL or greater.

The hyperinsulinemic euglycemic clamp is a blood test in which intravenous insulin followed by intravenous glucose solution is given over two hours as blood glucose levels are measured. The glucose is adjusted until the blood glucose reaches a normal level.

In an insulin sensitive person, a large amount of glucose is needed to maintain a normal blood glucose level. Individuals with greater levels of insulin resistance require less glucose to maintain a normal blood glucose level.

Treatment & Therapy

There is currently no FDA-approved prescription drug that has been approved for treating insulin resistance. Since insulin resistance means the body has excess blood sugar, blood-sugar lowering medications that are used for prediabetes and diabetes can prove useful. One of the most commonly prescribed drugs for this purpose is metformin. It increases cell sensitivity to insulin.

Some less commonly prescribed drugs either slow the rise in blood sugar levels after meals or directly increase insulin production. Although medications are very powerful, research has proven they must be combined with exercise and weight loss to have the maximum impact on reducing insulin resistance. Smoking cessation can also decrease insulin resistance.

Prevention & Prophylaxis

Eating a balanced, portion-controlled diet that is low in fat and sodium yet rich in whole foods, such as fresh fruit and vegetables, will result in a healthier weight. Such a diet will also provide nutritional support needed for optimal function. For example, an adequate supply of vitamin D, possibly through supplements, will help make cells more sensitive to insulin.

Exercise is a powerful, proven method of reducing insulin resistance. It works primarily because it reduces body weight, increases circulation and improves cell sensitivity to insulin. Aiming for at least 30 minutes of activity per day can have a powerful role in preventing disease. Incorporating aerobic exercise, strength training, and flexibility exercises for maximum benefit.