Insulin resistance is a decrease in the susceptibility of insulin–sensitive tissues to the action of insulin with sufficient concentration in the blood. There are no specific symptoms of insulin resistance. Common concomitant signs are: visceral obesity, arterial hypertension, fatty hepatosis, atherosclerosis, black acanthosis (pigmented wrinkled areas of the skin). Laboratory tests are used for diagnosis: oral glucose tolerance test, intravenous version of glucose tolerance test, calculation of HOMA-IR index. The main ways to correct insulin resistance are compliance with the rules of a balanced diet, systematic physical training.
ICD 10
R73.0 E11
Meaning
The term “insulin resistance” was introduced into medicine in 1992 to designate a factor that causes a complex of metabolic disorders, which include hypertension, diabetes mellitus, hypertriglyceridemia and visceral obesity. Since 1999, the term “metabolic syndrome” has been used in the same meaning. According to 2001 studies, the prevalence of pathological insulin resistance among healthy women is 10%, among men – 15%. In people with impaired glucose tolerance, the indicators are 42% and 64%, in patients with diabetes – 78% and 84%, respectively. High epidemiological data indicate the need to develop express diagnostic methods and introduce them into clinical endocrinology.
Causes
Reduced insulin reactivity of tissues can be triggered by many factors – age-related changes, pregnancy, physical inactivity, puberty, weight gain, infectious process, stress, fasting, uremia, liver cirrhosis, ketoacidosis, endocrine diseases. The most common causes of insulin resistance include:
- Excessive intake of sugar. When eating foods containing a large amount of refined sugar, the body begins to produce insulin more actively. The sensitivity of cells to its effects decreases, and the amount of glucose remains elevated.
- Fatness. Adipose tissue has an endocrine and paracrine function – it produces substances that affect the insulin susceptibility of cells. In obesity, the interaction of the hormone with receptors and intracellular glucose transport is disrupted.
- Genetic burden. The factor of predisposition to insulin resistance is heredity. Disorders of carbohydrate metabolism are found in people whose direct relatives have a diagnosis of diabetes mellitus, obesity or arterial hypertension.
Pathogenesis
Insulin resistance develops when the most insulin-sensitive tissues – liver, fat and muscle tissue – lose the ability to perceive the action of this hormone. Several leading pathological mechanisms have been identified: an increase in the level of free fatty acids, chronic hyperglycemia, chronic inflammation of adipose tissues, oxidative metabolic stress, changes in gene expression and mitochondrial dysfunction.
Free fatty acids (FFA) are a substrate for the synthesis of triglycerides, which are insulin antagonists. When the concentration of FFA increases and the metabolism of triglycerides in myocytes changes, the number of glucose transporters decreases, glucose is broken down more slowly. In the liver, excessive intake of FFA inhibits the processes of glucose transfer and phosphorylation. Insulin does not inhibit gluconeogenesis, glucose production by hepatocytes increases. With insulin resistance, the synthesis and secretion of VLDL increases, the concentration of HDL decreases. Due to the high level of FFA, lipids accumulate in the cells of the pancreas, disrupting their hormonal function. The anti-lipolytic effect of insulin is reduced in adipose tissue. Obesity is characterized by an aseptic inflammatory process in adipocytes, oxidative stress and hyperglycemia are formed.
Classification
The sensitivity of body tissues to the effects of insulin is determined by various factors – age, body weight, fitness of the body, the presence of bad habits and diseases. Insulin resistance is detected in type 2 diabetes and a number of other diseases and functional conditions, which are based on metabolic disorders. Depending on this factor , four types of insulin resistance are distinguished in endocrinology:
- Physiological. It is a mechanism of adaptation to periods of changing energy intake and release. Occurs during night sleep, pregnancy, puberty, in old age, with frequent consumption of fatty foods.
- Metabolic. It is diagnosed with dysmetabolic disorders. It is characteristic of type II diabetes, decompensated type I diabetes, diabetic ketoacidosis, prolonged nutritional deficiency, alcohol intoxication, obesity.
- Endocrine. It is caused by pathologies of the endocrine glands. It is determined with thyrotoxicosis, hypothyroidism, Cushing’s syndrome, acromegaly, pheochromocytoma.
- Pathological non-endocrine. It is aimed at preserving homeostasis in diseases and some emergency conditions. It accompanies arterial hypertension, CRF, cirrhosis of the liver, oncological cachexia, burn disease, blood poisoning, surgical operations.
Insulin resistance symptoms
Insulin resistance is not clinically manifested, but it develops on the basis of certain characteristics of the body, provokes metabolic disorders, changes the work of internal organs. Therefore, with regard to insulin resistance, it is worth talking not about the symptoms, but about the accompanying signs. Excessive fat deposition is observed, especially often in the waist area. This type of obesity is called abdominal. Visceral fat accumulates around the organs, affects their functions. Another common sign is high blood pressure, manifested by headache in the occipital part, dizziness, confusion, palpitations, sweating, redness of the face.
Fluctuations in blood sugar levels lead to the fact that patients feel tired, weak, depressed, irritable, experience increased thirst and hunger. The skin may have a specific pigmentation – black keratosis (acanthosis). Areas of skin on the neck, sides, in the armpits, under the mammary glands darken, become rough and wrinkled, sometimes peel off. In women, insulin resistance is often accompanied by symptoms of hyperandrogenism, which arose on the basis of polycystic ovary syndrome. Characteristic signs are oily seborrhea, vulgar acne, menstrual cycle disorders, the appearance of excessive hair on the hands, feet and face.
Complications
The most common consequences of insulin resistance are cardiovascular diseases and diabetes. With insulin resistance and obesity, the function of insulin to cause vasodilation decreases, and the inability of the arteries to dilate is the initial stage of the development of angiopathies (circulatory disorders). Insulin resistance also contributes to the formation of atherosclerosis, as it changes the activity of blood clotting factors and the process of fibrinolysis. The mechanism of development of type II diabetes as a complication of insulin resistance is prolonged compensatory maintenance of hyperinsulinemia and subsequent depletion of beta cells, reduction of insulin synthesis, formation of persistent hyperglycemia.
Diagnostics
Detection of insulin resistance is a complex diagnostic task due to the fact that this condition has no specific clinical manifestations, does not encourage patients to seek medical help. As a rule, it is detected during an examination by an endocrinologist for diabetes mellitus or obesity. The most common diagnostic methods are:
- Insulin suppressive test. The method is based on prolonged administration of glucose, simultaneous suppression of the reaction of β-cells and the production of endogenous glucose. Insulin sensitivity is determined by the level of glucose in the equilibrium state. When the value of the MI index is ≥7.0, insulin resistance is confirmed.
- Oral glucose tolerance test. It is widely used in the framework of screening, determines the presence and severity of hyperinsulinemia. Blood serum levels of glucose, C-peptide, and insulin are measured on an empty stomach and after taking carbohydrates. Two hours after the carbohydrate load, in hyperinsulinemia, the insulin index is more than 28.5 microns/ml, in metabolic syndrome, the C–peptide index is more than 1.4 nmol/l, in diabetes mellitus, the glucose index is more than 11.1 mmol/L.
- Intravenous glucose tolerance test. Allows you to evaluate the phases of insulin secretion, reproduce the physiological model of its action. During the procedure, glucose and insulin are injected intravenously according to the scheme, the results reflect changes in glucose regardless of insulin and under its action. Insulin resistance is determined by the SI -4 min -1 index.
- The HOMA-IR index. Before calculating the coefficient, a blood test is performed, indicators of the amount of insulin, sugar (glucose) in the fasting blood plasma are used. The presence of insulin resistance is indicated by an index above 2.7.
Insulin resistance treatment
Medical care is provided to patients in a comprehensive manner. It is aimed not only at strengthening the insulin response of tissues, but also at normalizing the concentration of glucose, cholesterol, blood insulin, eliminating excess weight, preventing obesity, diabetes, heart and vascular diseases. The treatment is carried out by an endocrinologist, a nutritionist, a physical therapy instructor. Patients are shown:
- Drug therapy. Medications are prescribed to patients with a body mass index of more than 30, who have a high risk of cardiovascular diseases. To reduce weight and increase insulin sensitivity, biguanides, alpha-glucosidase blockers, and thiazolidinediones are used.
- A low-carb diet. People with insulin resistance are shown a low-carbohydrate diet, but without periods of fasting. The diet is fractional – from 5 to 7 meals a day in small portions. This scheme allows you to maintain a stable sugar level, relatively uniform insulin activity.
- Regular physical activity. Exercise activates glucose transport and insulin’s ability to stimulate glycogen synthesis. The training regime is selected individually for patients: from athletic walking and light gymnastics to strength and aerobic training. The main condition is the regularity of classes.
Prognosis and prevention
The state of insulin resistance can be corrected with a comprehensive approach, including adherence to a diet and a physical activity regime. When all doctors’ prescriptions are fulfilled, the prognosis is often favorable. For the purpose of prevention, it is necessary to control the intake of carbohydrates, especially industrially processed sugar, avoid inactivity, and with a sedentary lifestyle – purposefully introduce sports training into the daily routine. It is important for obese people to focus on weight loss. In the presence of hereditary burden of diabetes mellitus, atherosclerosis, periodic monitoring of glucose, insulin, and blood cholesterol is recommended.