What Causes Diabetes, and What Are Its Symptoms and Complications?
Diabetes is one of modern medicine’s most persistent and destructive metabolic diseases.
It is a condition in which blood glucose remains abnormally high because the pancreas produces too little of the hormone insulin, or because the body develops insulin resistance and cells fail to respond to it properly.
Diabetes is far more than sugar appearing in the urine. Persistently elevated blood glucose damages capillaries and major blood vessels throughout the body, causing potentially devastating chronic complications.
This article examines in detail the causes of diabetes, its physical symptoms and the mechanisms behind its potentially fatal complications, while providing a comprehensive overview of medical treatments and everyday prevention strategies.
1. What Causes Diabetes?
Depending on how it develops and its underlying characteristics, diabetes is generally classified as type 1 diabetes, type 2 diabetes,
or gestational diabetes. Each type has different causes.
[Major Causes of Diabetes]
├── Type 1 diabetes ── Autoimmune response ── Destruction of pancreatic beta cells (insulin deficiency)
└── Type 2 diabetes ── Genetic + environmental factors ── Increased insulin resistance & reduced insulin secretion
├── Environmental factors: obesity, high-fat diet, lack of exercise, aging, stress
Type 1 Diabetes: An Autoimmune Disorder
Type 1 diabetes accounts for a minority of diabetes cases. It was once commonly called “juvenile diabetes,” but it can develop in adults as well.
It is an autoimmune disease in which the body’s immune system mistakenly identifies the pancreas’s insulin-producing beta cells as a threat and destroys them. Possible triggers include genetic susceptibility and infections such as coxsackievirus.
As a result, the body produces little to no insulin, making external insulin essential for survival.
Type 2 Diabetes: A Combination of Genetic and Environmental Factors
Type 2 diabetes accounts for more than 90 percent of diabetes cases in South Korea and develops through a combination of factors.
- Genetic factors: Family history plays a major role. If one parent has diabetes, the child’s risk is estimated at 15 to 20 percent. If both parents have diabetes, the risk rises to between 30 and 50 percent.
- Obesity and insulin resistance: Obesity driven by a Western-style diet high in fat and carbohydrates can dramatically increase insulin resistance. When fat accumulates in cells, it interferes with insulin’s ability to move glucose into them, causing blood glucose levels to rise.
- Lack of exercise and sarcopenia: Muscles are the body’s largest consumer of glucose, using roughly 70 percent or more of it. When physical activity declines and muscle mass falls with age, there is less tissue available to absorb glucose from the bloodstream, increasing the risk of diabetes by as much as 30 to 57 percent.
- Aging and stress: Pancreatic function naturally declines with age. Excessive psychological stress also stimulates the release of cortisol and adrenaline, which can directly interfere with insulin’s action.
2. Key Signs and Symptoms of Diabetes
When glucose levels become excessive, the body sends powerful warning signals as it attempts to eliminate the excess and maintain normal metabolism.
The classic symptoms of diabetes are the “three polys”—frequent urination, excessive thirst and increased hunger—along with sudden changes in weight.
The “Three Polys”
- Polyuria (excessive urination): When blood glucose exceeds the kidneys’ reabsorption threshold, glucose is excreted in the urine. Because glucose draws water with it through osmosis, people urinate more often and in greater volumes.
- Polydipsia (excessive thirst): As the body rapidly loses water through frequent urination, it recognizes severe dehydration. The brain’s thirst center is stimulated, leading to an almost constant desire to drink and the consumption of large amounts of fluid.
- Polyphagia (excessive hunger): When insulin does not work properly, glucose cannot enter cells even after a meal. The cells remain chronically starved of energy, prompting the brain to send persistent hunger signals.
Unexplained Weight Loss and Fatigue
Even when a person eats enough, the cells may be unable to use glucose as fuel. As an emergency measure, the body begins to break down stored fat and protein for energy.
As a result, several kilograms can be lost within weeks without any deliberate effort, while depleted energy reserves lead to severe chronic fatigue and weakness throughout the body.
Other Systemic Signs
Damage to blood vessels can cause tiny areas of swelling in the retina, resulting in blurred vision and impaired eyesight.
Poor peripheral circulation and reduced immune function can also make wounds slow to heal and prone to infection. Fungal infections of the skin and vagina may occur more frequently as well.
3. Serious Complications Caused by Diabetes
The real danger of diabetes lies not only in high blood glucose itself, but in the complications that travel through the bloodstream and damage the entire body.
These complications generally fall into two categories: acute metabolic complications and long-term chronic vascular complications.
[Types of Diabetes Complications]
├── Acute complications ── Ketoacidosis / Hyperosmolar hyperglycemic state (life-threatening loss of consciousness)
└── Chronic complications
├── Microvascular disease ── Retinopathy (blindness) / Nephropathy (dialysis) / Neuropathy (pain, paralysis)
└── Macrovascular disease ── Myocardial infarction / Stroke / Peripheral artery disease (diabetic foot necrosis)
Acute Complications: Life-Threatening Emergencies
- Diabetic ketoacidosis (DKA): This occurs primarily in people with type 1 diabetes. When there is little or no insulin, the body breaks down fat excessively for energy, producing acidic substances called ketone bodies that accumulate in the blood. The resulting acidosis can cause breathing difficulties, vomiting and impaired consciousness. Without immediate treatment, it can be fatal.
- Hyperosmolar hyperglycemic state (HHS): Seen primarily in people with type 2 diabetes, HHS is characterized by extremely high blood glucose—typically 600 mg/dL or higher. The resulting increase in urination can cause severe dehydration and coma.
Chronic Microvascular Complications: Damage to Major Organs
When high blood glucose persists for years, the body’s smallest blood vessels are often damaged first.
- Diabetic retinopathy: Blocked or ruptured blood vessels in the retina can trigger the growth of abnormal new vessels and lead to vision loss. It is the leading cause of blindness among adults.
- Diabetic nephropathy: Damage to the glomerular capillaries that filter waste from the blood can cause protein to appear in the urine. In advanced cases, it can progress to chronic kidney failure, requiring lifelong dialysis or a kidney transplant.
- Diabetic neuropathy: High blood glucose damages nerve cells and the blood vessels that supply them. Symptoms may include numbness and stabbing pain in the fingers and toes—or, conversely, complete loss of sensation.
Chronic Macrovascular Complications: Deadly Cardiovascular Disease
Sticky, glucose-laden blood promotes the buildup of plaque in the walls of major arteries, accelerating atherosclerosis.
- Cardiovascular and cerebrovascular disease: Compared with people without diabetes, those with the condition are more than two to four times as likely to develop heart attacks, angina and stroke, making these complications a major cause of death.
- Peripheral artery disease and diabetic foot ulcers: When the peripheral arteries supplying the legs become blocked and nerve damage causes numbness, people may not notice injuries to their feet. Wounds can deteriorate into foot necrosis, sometimes leading to amputation.
4. Diagnostic Criteria for Diabetes
Because diabetes often causes vague symptoms—or none at all—it must be diagnosed through detailed blood testing to determine whether the relevant criteria are met.
| Test | Normal range | Prediabetes | Diabetes |
|---|---|---|---|
| Fasting blood glucose (at least 8 hours without food) | Below 100 mg/dL | 100–125 mg/dL | 126 mg/dL or higher |
| Hemoglobin A1c (HbA1c) (average blood glucose over 2–3 months) | 5.6% or lower | 5.7–6.4% | 6.5% or higher |
| Two-hour post-meal blood glucose (oral glucose tolerance test) | Below 140 mg/dL | 140–199 mg/dL | 200 mg/dL or higher |
5. Managing and Treating Diabetes
The central goal of diabetes treatment is not simply to control glucose readings, but to prevent chronic complications through comprehensive lifestyle changes and carefully tailored medication.
[The Three Pillars of Diabetes Treatment]
├── 1. Nutrition therapy ── Reduce advanced glycation products; emphasize complex carbohydrates and dietary fiber
├── 2. Exercise therapy ── Combine aerobic and strength training (build muscle and use glucose)
└── 3. Medication ── Oral glucose-lowering drugs (type 2) / Insulin injections (type 1 and advanced type 2)
Nutrition Therapy: Minimizing Blood Glucose Fluctuations
Nutrition therapy is not simply about restricting calories. It is about establishing eating habits that raise blood glucose gradually.
- Eat fiber first: Starting a meal with fiber-rich foods such as vegetables and seaweed can slow the rate at which glucose is absorbed through the intestinal wall, helping prevent a post-meal glucose spike.
- Limit refined carbohydrates: Minimize simple sugars found in white rice, flour, sugar and high-fructose corn syrup, and choose complex carbohydrates in the form of whole grains such as brown rice, barley and whole wheat.
- Balance protein and unsaturated fats: High-quality lean meat, fish and tofu can help prevent muscle loss and support glucose metabolism.
Exercise Therapy: Helping the Body Use Glucose
Exercise improves insulin sensitivity, helping glucose move from the bloodstream into muscle cells even without insulin.
- Types of exercise: Aerobic activities such as brisk walking, cycling and swimming should be combined with strength training, including squats, dumbbell exercises and resistance-band workouts. The more muscle mass a person has, the larger the body’s “glucose storage capacity.”
- Exercise duration: At least 150 minutes of moderate-intensity aerobic exercise per week, along with strength training two to three times a week, is recommended. Starting exercise 30 minutes to one hour after a meal—when blood glucose is approaching its peak—can be particularly effective for lowering post-meal levels.
Medical Treatment: Tailoring Therapy to the Patient
When lifestyle changes alone do not provide adequate control, active drug treatment prescribed by a doctor may be necessary.
- Oral glucose-lowering drugs (type 2 diabetes): Depending on factors such as obesity and pancreatic function, doctors may prescribe combinations of metformin, which suppresses glucose production in the liver; sulfonylureas, which stimulate insulin secretion by the pancreas; SGLT2 inhibitors, which force glucose out through the urine; and DPP-4 inhibitors.
- Insulin therapy: People with type 1 diabetes, whose bodies cannot produce insulin, require lifelong insulin injections or an insulin pump. People with type 2 diabetes may also need temporary or permanent insulin treatment if pancreatic function has been severely depleted or acute complications have developed.
6. Comprehensive Diabetes Prevention
Once diabetes develops and pancreatic cells are damaged, it is very difficult to restore the body to its previous state. The best approach is therefore rigorous prevention during the prediabetes stage or while a person is in a high-risk group because of family history.
1. Maintain a Healthy Weight and Waistline
Obesity is a key environmental factor driving insulin resistance. Losing just 5 percent of current body weight can reduce the likelihood of progressing to type 2 diabetes by more than 50 percent. Particular attention should be paid to waist circumference, a measure of visceral fat: below 90 cm for men and below 85 cm for women.
2. Move More and Avoid a Sedentary Lifestyle
Spending long periods sitting or lying down can impair insulin function.
Make a habit of taking the stairs instead of the escalator and walking regularly for 30 minutes a day at least five days a week.
Avoid sitting continuously for more than 90 minutes; stand up and move around frequently.
3. Limit Alcohol and Never Smoke
Alcohol is high in calories, contributes to fatty liver disease and obesity, and can directly cause inflammation of the pancreas.
Nicotine in cigarettes stimulates the sympathetic nervous system, raising blood glucose and rapidly worsening atherosclerosis, a major driver of chronic complications. People with diabetes and those at risk should therefore quit smoking.
4. Improve Sleep and Manage Stress
Lack of sleep directly increases insulin resistance. Going to bed around 11 p.m. and getting seven to eight hours of quality sleep each night can help stabilize blood glucose.
Stress hormones such as cortisol should also be kept in check through meditation, hobbies and other stress-management activities.
5. Get Regular Blood Glucose Screening
Because diabetes causes few symptoms in its early stages, regular screening is essential.
All adults aged 35 and older—and anyone aged 19 or above with metabolic syndrome, obesity or a family history of diabetes—should have annual fasting glucose and HbA1c tests to identify blood glucose abnormalities early.
7. Summary and Conclusion
✅ Diabetes is a chronic metabolic disease in which impaired insulin function in the pancreas causes glucose to build up in the bloodstream and damage blood vessels throughout the body. It can be effectively controlled and its complications prevented through nutrition therapy, exercise, medication and maintaining a healthy weight.
Diabetes is not a temporary condition that can be cured with a single treatment. It is a lifestyle-related disease that must be managed throughout life.
Do not dismiss warning signs such as the three polys or unexplained weight loss. Seek a prompt medical evaluation.
Even after receiving a diabetes diagnosis, there is no reason to lose heart.
Instead, use it as an opportunity to take a closer look at your health. With careful dietary management, regular strength and aerobic exercise, and appropriate medical treatment, you may be able to lead a healthier and more energetic life than ever.
