What Is Diabetes? Symptoms, Types, Diagnosis and Treatment

Created: 15.08.2024 · Last Updated: 17.08.2026 · Category: Endocrinology and Metabolism · Prepared by the Academic Hospital Web and Editorial Board.

What Is Diabetes?

Diabetes mellitus is a group of metabolic diseases characterised by chronically elevated blood glucose.

Insulin is a hormone produced by pancreatic beta cells and plays a central role in regulating how glucose is used and stored.

Diabetes develops when insulin production is severely reduced or absent, when the body does not respond adequately to insulin, or when both mechanisms occur together.

Over time, poorly controlled diabetes can damage blood vessels and affect the heart, kidneys, eyes and nervous system.

Diabetes management is not simply about lowering blood glucose. Modern care also considers cardiovascular and kidney health, weight, blood pressure, lipids, hypoglycaemia risk and quality of life.

What Are the Types of Diabetes?

The main categories are:

  • Type 1 diabetes
  • Type 2 diabetes
  • Gestational diabetes mellitus
  • Other specific types of diabetes

Other specific types include certain monogenic diabetes syndromes, diabetes caused by diseases of the exocrine pancreas and diabetes induced by some medicines or chemicals.

Type 1 diabetes is not exclusively a childhood disease, and Type 2 diabetes is not exclusively an adult disease. Both can occur across different age groups.

What Is Type 1 Diabetes?

Type 1 diabetes is usually an autoimmune disease in which the immune system damages the insulin-producing beta cells of the pancreas.

This leads to severe or near-absolute insulin deficiency.

Type 1 diabetes may begin in childhood, adolescence or adulthood.

People with Type 1 diabetes require insulin replacement for survival and metabolic control.

Insulin can be delivered through multiple daily injections, insulin pumps and other appropriate delivery methods according to individual circumstances.

What Is Type 2 Diabetes?

Type 2 diabetes develops when insulin resistance is accompanied by a progressive inability of the pancreatic beta cells to produce enough insulin to meet the body's needs.

Genetic susceptibility and metabolic and environmental factors interact in its development.

Overweight and obesity, physical inactivity and increasing age can increase risk, although Type 2 diabetes can also occur in people with a normal body weight.

Type 2 diabetes can also occur in children and adolescents.

What Is Gestational Diabetes?

Gestational diabetes mellitus is diabetes generally diagnosed during the second or third trimester of pregnancy in a person who did not have clearly established diabetes before pregnancy.

It can be associated with risks for both mother and baby and therefore requires appropriate glucose monitoring and treatment.

Although glucose levels may return to normal after delivery, a history of gestational diabetes is associated with an increased future risk of Type 2 diabetes, so continued follow-up is important.

What Are the Symptoms of Diabetes?

Diabetes can cause obvious symptoms, but Type 2 diabetes in particular may remain asymptomatic for a long time.

Symptoms of marked hyperglycaemia may include:

  • Excessive thirst
  • Frequent urination
  • Increased hunger
  • Unexplained weight loss
  • Fatigue
  • Blurred vision
  • Slow wound healing
  • Recurrent infections

Numbness or tingling in the hands and feet may occur as a complication of longer-term diabetes-related nerve damage.

Having no symptoms does not exclude diabetes. Prediabetes and Type 2 diabetes can remain clinically silent for years.

What Causes Diabetes?

The cause depends on the type of diabetes.

Type 1 diabetes is primarily associated with autoimmune destruction of pancreatic beta cells in genetically susceptible individuals.

Type 2 diabetes results from a complex interaction between genetic susceptibility, insulin resistance, progressive beta-cell dysfunction and metabolic and environmental factors.

Type 1 diabetes is not caused by eating too much sugar, and Type 2 diabetes should not be reduced to a simple consequence of an individual's dietary choices.

What Increases the Risk of Type 2 Diabetes?

  • Overweight or obesity
  • Physical inactivity
  • Family history of Type 2 diabetes
  • Prediabetes
  • A history of gestational diabetes
  • Hypertension
  • Certain lipid disorders
  • Polycystic ovary syndrome
  • Increasing metabolic risk with age

How Is Diabetes Diagnosed?

In nonpregnant individuals, diabetes may be diagnosed using:

  • A1C ≥6.5%
  • Fasting plasma glucose ≥126 mg/dL
  • 2-hour plasma glucose ≥200 mg/dL during a 75-g oral glucose tolerance test
  • Random plasma glucose ≥200 mg/dL in a person with classic symptoms of hyperglycaemia or a hyperglycaemic crisis

In the absence of unequivocal hyperglycaemia, an abnormal result generally requires confirmation.

A home glucose-meter reading alone does not establish a definitive diagnosis of diabetes. Diagnosis should be confirmed using appropriate laboratory testing.

What Is Prediabetes?

Prediabetes refers to glucose levels that are higher than normal but below the diagnostic range for diabetes.

It indicates an increased risk of developing Type 2 diabetes and may coexist with cardiovascular risk factors.

In appropriate high-risk adults with overweight or obesity, structured programmes targeting approximately 5–7% weight reduction and at least 150 minutes per week of moderate-intensity physical activity can help delay or prevent Type 2 diabetes.

How Is Diabetes Treated?

Treatment is individualised according to diabetes type, age, glucose levels, disease duration, body weight, cardiovascular and kidney health, risk of hypoglycaemia and other medical conditions.

Management may include:

  • Diabetes self-management education
  • Medical nutrition therapy
  • Physical activity
  • Weight management
  • Glucose-lowering medication
  • Insulin when required
  • Glucose-monitoring technologies
  • Management of cardiovascular and kidney risk factors

How Is Type 1 Diabetes Treated?

Insulin therapy is essential in Type 1 diabetes.

Treatment may involve:

  • Multiple daily insulin injections
  • Insulin-pump therapy
  • Continuous glucose monitoring
  • Automated insulin delivery systems
  • Carbohydrate and meal-management education
  • Adjustment for exercise and illness

How Is Type 2 Diabetes Treated?

Type 2 diabetes treatment is person-centred.

Healthy eating, physical activity and weight management remain important, but many people also require pharmacological therapy from the time of diagnosis.

Medication options can include:

  • Metformin
  • SGLT2 inhibitors
  • GLP-1 receptor agonists
  • Dual GIP/GLP-1 receptor agonists
  • DPP-4 inhibitors
  • Sulfonylureas
  • Thiazolidinediones
  • Insulin

Medication selection also considers cardiovascular disease, heart failure, chronic kidney disease, obesity, liver disease, hypoglycaemia risk, adverse effects, treatment burden, access and individual preferences.

Modern Type 2 diabetes therapy is not based solely on lowering glucose. In appropriate patients with cardiovascular disease, heart failure or chronic kidney disease, SGLT2 inhibitors and/or GLP-1–based therapies may be selected for cardiovascular and kidney benefits irrespective of A1C.

CGM, Insulin Pumps and Automated Insulin Delivery

Continuous glucose monitoring (CGM) tracks glucose throughout the day and can help identify high glucose, low glucose and glucose trends.

Insulin pumps continuously deliver programmed insulin.

Automated insulin delivery (AID) systems combine CGM, an insulin pump and an algorithm that automatically adjusts insulin delivery according to glucose data.

The choice of technology should be individualised according to clinical need, preferences, ability to use the device safely and access to appropriate training and support.

Which Organs Can Diabetes Affect?

Long-term diabetes may affect:

  • The heart and blood vessels
  • The kidneys
  • The retina and other structures of the eye
  • Peripheral nerves
  • The feet and wound healing

Managing blood pressure, lipids, smoking and kidney risk is therefore important in addition to glycaemic management.

What Is Monitored in Diabetes Care?

Depending on individual needs, follow-up may include:

  • A1C and glucose levels
  • CGM data
  • Hypoglycaemia
  • Blood pressure
  • Lipids
  • Kidney function and urine albumin
  • Eye examinations
  • Neuropathy and foot assessment
  • Body weight
  • Nutrition and physical activity

Which Departments Manage Diabetes?

Diabetes care may involve several disciplines according to the individual's needs.

  • Endocrinology and Metabolism
  • Internal Medicine
  • Paediatric Endocrinology for children and adolescents
  • Nutrition and Dietetics
  • Ophthalmology
  • Nephrology
  • Cardiology
  • Other specialties according to complications and clinical need
Not every person with diabetes needs routine assessment by every specialty. Referrals should be based on individual risks, complications and clinical needs.

When Is Urgent Medical Assessment Needed?

  • Loss of consciousness or altered mental status
  • Severe hypoglycaemia that does not resolve appropriately
  • Very high glucose with nausea, vomiting or abdominal pain
  • Rapid or deep breathing
  • Severe dehydration
  • Elevated ketones
  • Marked drowsiness or confusion

These symptoms may occur with diabetic ketoacidosis, hyperosmolar hyperglycaemic state or severe hypoglycaemia.

Have Your Blood Glucose and Diabetes Risk Assessed

If you have elevated blood glucose, prediabetes or risk factors for diabetes, appropriate laboratory testing and an individualised metabolic assessment can be planned.

Frequently Asked Questions

What is diabetes?
Diabetes is a group of metabolic diseases in which blood glucose is chronically elevated because insulin production is insufficient, insulin action is impaired or both mechanisms occur together.
What are the main types of diabetes?
The main categories are Type 1 diabetes, Type 2 diabetes, gestational diabetes and other specific types such as monogenic diabetes and diabetes caused by pancreatic disease or certain medicines.
Does Type 1 diabetes only occur in children?
No. Type 1 diabetes commonly begins in childhood or adolescence but can also develop in adulthood.
Does Type 2 diabetes only occur in people with overweight or obesity?
No. Overweight and obesity are important risk factors, but genetic and metabolic factors mean that Type 2 diabetes can also occur in people with a normal body weight.
How is diabetes diagnosed?
Diabetes may be diagnosed using A1C, fasting plasma glucose, a 75-g oral glucose tolerance test or random plasma glucose in the presence of classic hyperglycaemic symptoms. In the absence of unequivocal hyperglycaemia, confirmation is generally required.
Can Type 1 diabetes be treated without insulin?
No. People with Type 1 diabetes have severe insulin deficiency and require insulin treatment. Multiple injections, insulin pumps and automated insulin delivery systems may be used according to individual needs.
Does everyone with Type 2 diabetes need insulin?
No. Type 2 diabetes can be treated with lifestyle interventions and a range of non-insulin medicines. Insulin may be required when hyperglycaemia is severe, insulin deficiency becomes significant or other clinical circumstances make insulin appropriate.
Can diabetes be completely cured?
Type 1 diabetes currently requires lifelong insulin treatment. Some people with Type 2 diabetes can achieve remission after substantial weight loss and appropriate treatment, but remission is not regarded as a permanent cure and ongoing follow-up remains necessary.
Who can use continuous glucose monitoring?
CGM is particularly useful for people using insulin and is an important treatment technology in Type 1 diabetes from early in the course of the disease. Suitability is determined according to the individual's treatment and needs.
Academic Hospital note: Diabetes treatment involves more than lowering blood glucose. Cardiovascular and kidney health, body weight, blood pressure, lipid levels, hypoglycaemia risk and diabetes complications should be assessed together. You can book an appointment.

References

  1. Academic Hospital. Diabetes
  2. American Diabetes Association. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes—2026
  3. American Diabetes Association. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes—2026
  4. American Diabetes Association. Diabetes Technology: Standards of Care in Diabetes—2026
  5. American Diabetes Association. Prevention or Delay of Diabetes and Associated Comorbidities: Standards of Care in Diabetes—2026