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Lecture 8: Insulin Resistance and Type 2 Diabetes

Lecture Overview

Lecture 8: Insulin Resistance and Type 2 Diabetes

  • Course: KHPM324 Chronic Diseases of Modern Society

  • Presenter: Hannah Oh, ScD, Division of Health Policy & Management, College of Health Sciences, Korea University

Definition of Diabetes

  • Diabetes: A metabolic disorder that arises when the pancreas either:

    • Fails to produce sufficient insulin, or

    • The body is incapable of effectively utilizing the insulin produced

  • Insulin: A hormone synthesized by the pancreas, crucial for facilitating glucose entry into cells for energy use.

    • Mechanism:

    • Insulin allows glucose in the blood to enter cells.

    • Inability to produce or effectively use insulin leads to elevated blood glucose levels.

    • Chronic high blood glucose levels can cause damage to the body and result in organ failure.

Types of Diabetes

Type 1 Diabetes

  • Rapid onset of symptoms.

  • Requires insulin therapy for survival.

Type 2 Diabetes

  • Constitutes at least 90% of all diabetes cases.

  • Can manifest at any age, though commonly adult-onset.

  • Characterized by:

    • Insulin resistance and/or relative insulin deficiency.

    • Often linked to obesity or overweight.

  • Management:

    • Initial management may involve lifestyle changes (diet and exercise).

    • Long-term, many patients require oral medications or insulin therapy.

Glucose and Insulin Regulation in a Normal Body

  1. Consumption of food leads to the breakdown of carbohydrates into blood sugar.

  2. Blood sugar enters the bloodstream, prompting the pancreas to release insulin.

  3. Insulin facilitates blood sugar entry into the body’s cells for energy use.

  4. Insulin signals the liver to store blood sugar for future use.

  5. As blood sugar enters cells, levels in the bloodstream drop, signaling a decrease in insulin production.

  6. Decreased insulin levels notify the liver to release stored blood sugar for energy availability when not eating.

Insulin Resistance

Mechanism Leading to Insulin Resistance

  1. Significant amounts of blood sugar flood into the bloodstream.

  2. The pancreas compensates by producing more insulin to facilitate glucose entry into cells.

  3. Over time, cells become resistant to insulin, diminishing their response.

  4. The pancreas continues to produce an increasing amount of insulin trying to stimulate cell response.

  5. Eventually, the pancreas's ability to produce insulin wanes, resulting in continued elevation of blood sugar and paving the way for prediabetes or diabetes.

Effects of Insulin Resistance

  • Implications of Insulin Resistance:

    • Results in:

    • Constant high glucose levels in blood.

    • Constant high demand for insulin.

    • Cells becoming starved due to ineffective glucose entry.

    • Leading to feelings of hunger and cravings.

Processes Leading to Typical Symptoms of Diabetes

  1. Consumption of food containing starch or sugar causes carbohydrate breakdown into glucose.

  2. Glucose builds up in the bloodstream.

  3. The body attempts to eliminate excess glucose through various methods (example: frequent urination).

  4. Insufficient insulin release or resistance to insulin prevents glucose conversion into energy.

  5. Diagnosis of diabetes often follows the manifestation of common symptoms: weight loss, fatigue, excessive thirst.

Diabetic Retinopathy

  • Diabetic Retinopathy:

    • Health risks posed to the eyes due to diabetes.

    • Healthy blood vessels can leak fluids in the retina, leading to compromised vision.

Diagnostic Criteria for Diabetes and Prediabetes

Fasting Plasma Glucose Test (FPG)

  • Normal: < 100 mg/dL

  • Pre-diabetes: 100-125 mg/dL

  • Diabetes: ≥ 126 mg/dL

Oral Glucose Tolerance Test (OGTT)

  • Normal: < 140 mg/dL

  • Pre-diabetes: 140-199 mg/dL

  • Diabetes: ≥ 200 mg/dL

A1C Test

  • Measure of average blood glucose over the previous three months:

    • Pre-diabetes: HbA1c 5.7%-6.4%

    • Diabetes: HbA1c ≥ 6.5%

Risk Factors for Insulin Resistance

  • Key Risk Factors:

    • Obesity, particularly abdominal or visceral fat.

    • High-sugar and processed food diet.

    • Physical inactivity.

    • Inflammation.

    • Poor sleep habits and conditions like sleep apnea.

    • Genetic predispositions.

Impact of Body Composition on Diabetes

  • Research indicates that obesity is a significant risk factor for diabetes, affecting men and women differently.

Lifestyle Factors and Type 2 Diabetes Risk

Physical Activity and Sedentary Lifestyle

  • Impact demonstrated through % change in diabetes risk relative to activity levels.

    • Examples:

    • Watching TV (2 hrs/day): -12% risk decrease

    • Brisk walking (1 hr): -34% risk decrease

Diet and Type 2 Diabetes

  • Strong correlation exists between diet and development of type 2 diabetes, highlighting the role of insulin resistance and obesity.

Glycemic Index (GI)

  • Glycemic Index: Value assigned to foods based on their impact on blood glucose levels.

    • Foods with a low GI:

    • Release glucose slowly, promoting better glucose control in diabetic patients.

    • Foods with a high GI:

    • Release glucose rapidly, useful for energy recovery post-exercise or mitigating hypoglycemia.

Relative Risk Factors for Diabetes

  • Analysis of dietary factors and their relative risk in developing type 2 diabetes linked to glycemic load and specific dietary fat ratios.

Sugar-sweetened Soft Drinks and Type 2 Diabetes

  • Statistical data shows increased risk (relative risk of 1.83) of developing type 2 diabetes with the consumption of sugar-sweetened soft drinks, emphasizing the correlation between diet and diabetes risk.

Type 2 Diabetes in Asia

  • Observation: Asians exhibit diabetes development at lower BMI thresholds, often linked to a “metabolically obese” phenotype despite normal weight.

  • Thrifty Genotype Hypothesis: Suggests a genetic advantage in times of nutrient scarcity, which may predispose individuals to obesity and diabetes amid modern over-nutrition.

Complications of Diabetes

  • Diabetes poses substantial health risks, which include:

    • Kidney disease.

    • Increased risks of heart disease, stroke, and certain cancers.

    • Nerve damage and impaired circulation.

    • Weakened immune response.

    • Inflammation and potential for increased mortality.

Treatment Options for Diabetes

  • Insulin: Primarily used for type 1 diabetes.

  • Metformin: Most frequently prescribed medication for type 2 diabetes, aimed at lowering blood sugar levels.

  • Other Medications:

    • Include SGLT2 inhibitors, which suppress renal glucose reabsorption, and various weight-loss medications.

  • Lifestyle Changes: Emphasis on healthy eating and regular exercise as critical components in managing diabetes.