Diabetes: Types, Symptoms, Risk Factors, Diagnosis and Prevention

Diabetes is a chronic condition that occurs when the level of glucose (sugar) in the blood becomes too high.

Glucose is an important source of energy for the body. A hormone called insulin, produced by the pancreas, helps glucose move from the bloodstream into cells where it can be used for energy.

Diabetes develops when the body:

• does not produce enough insulin,
• produces little or no insulin,
• does not use insulin effectively,
• or experiences a combination of these problems.

Without appropriate treatment, persistently high blood glucose can gradually damage different parts of the body.

However, diabetes can be effectively managed, and many complications can be prevented or delayed through appropriate treatment and ongoing healthcare.

How Common Is Diabetes?

Diabetes is a major global health condition.

According to the World Health Organization (WHO), the number of people living with diabetes increased from approximately 200 million in 1990 to 830 million in 2022.

The increase has been particularly rapid in low- and middle-income countries.

Type 2 diabetes accounts for the great majority of diabetes cases worldwide.

What Are the Main Types of Diabetes?

The three main types are:

• type 1 diabetes,
• type 2 diabetes,
• and gestational diabetes.

There are also less common forms of diabetes caused by genetic conditions, diseases affecting the pancreas, certain medicines and other medical conditions.

Each type develops differently and may require a different treatment approach.

What Is Type 1 Diabetes?

Type 1 diabetes is an autoimmune disease.

The immune system mistakenly attacks and destroys insulin-producing beta cells in the pancreas.

As a result, the body produces little or no insulin.

People with type 1 diabetes need insulin every day to survive.

Type 1 diabetes often develops during childhood or young adulthood, but it can develop at any age.

Can Type 1 Diabetes Be Prevented?

There is currently no established way to prevent type 1 diabetes.

Diet, body weight or a lack of exercise does not cause type 1 diabetes.

This distinction is important because people with type 1 diabetes should never be blamed for developing the condition.

Researchers continue to investigate why the autoimmune process develops and how the disease might eventually be prevented.

What Is Type 2 Diabetes?

Type 2 diabetes is the most common type.

It develops when cells do not respond normally to insulin—a condition called insulin resistance—and the pancreas cannot produce enough insulin to maintain blood glucose within a healthy range.

Blood glucose then begins to rise.

Type 2 diabetes usually develops gradually.

Some people can have it for years without realizing it because symptoms may be mild or absent.

Although historically associated primarily with adults, type 2 diabetes can also occur in children and adolescents.

What Is Prediabetes?

Prediabetes means blood glucose levels are higher than normal but not yet within the diagnostic range for diabetes.

Prediabetes increases the likelihood of developing type 2 diabetes.

It can also be associated with increased cardiovascular risk.

However, progression from prediabetes to type 2 diabetes is not inevitable.

Lifestyle changes and, in selected circumstances, medication can substantially reduce the likelihood of progression.

What Is Gestational Diabetes?

Gestational diabetes is high blood glucose first diagnosed during pregnancy in someone who did not already have known diabetes.

Pregnancy naturally changes the way the body responds to insulin.

In some people, the pancreas cannot produce enough additional insulin to compensate, causing blood glucose to rise.

Gestational diabetes often causes no obvious symptoms and is usually identified through prenatal screening.

Appropriate management is important for both the pregnant person and baby.

Does Gestational Diabetes Go Away?

Blood glucose often returns toward normal after pregnancy.

However, having gestational diabetes increases the future risk of developing type 2 diabetes.

Follow-up blood glucose testing after pregnancy and longer-term monitoring are therefore important.

Children born following pregnancies complicated by gestational diabetes may also have increased future metabolic health risks.

Other Types of Diabetes

Not every case fits into type 1, type 2 or gestational diabetes.

Other forms can include:

• monogenic diabetes caused by changes in a single gene,
• diabetes associated with diseases of the pancreas,
• diabetes related to certain endocrine conditions,
• cystic fibrosis-related diabetes,
• and diabetes caused by some medicines.

Correct classification matters because treatment can differ considerably.

What Are the Symptoms of Diabetes?

Common symptoms can include:

• urinating more frequently than usual,
• excessive thirst,
• increased hunger,
• unexplained weight loss,
• tiredness,
• blurred vision,
• sores or wounds that heal slowly,
• recurrent infections,
• and numbness or tingling in the hands or feet.

Not everyone experiences all of these symptoms.

Some people—particularly those with type 2 diabetes—may have no obvious symptoms.

Frequent Urination

When blood glucose becomes very high, the kidneys attempt to remove excess glucose through urine.

This can cause increased urination.

Frequent urination can then contribute to dehydration and increased thirst.

Someone who suddenly develops persistent excessive thirst and frequent urination should consider seeking medical assessment.

Increased Thirst

Excessive thirst is a classic symptom of diabetes.

It can result from the increased loss of fluid through frequent urination.

Drinking more water may relieve thirst temporarily, but it does not treat the underlying high blood glucose.

Persistent unexplained excessive thirst should be investigated.

Unexplained Weight Loss

Unexpected weight loss can occur when the body cannot use glucose normally for energy and begins using fat and muscle instead.

This is particularly characteristic of untreated type 1 diabetes but can occur with other forms.

Rapid unexplained weight loss accompanied by excessive thirst and frequent urination requires prompt medical assessment.

Blurred Vision

High blood glucose can temporarily alter fluid levels in tissues of the eye and cause blurred vision.

Long-term diabetes can also damage blood vessels in the retina, a condition known as diabetic retinopathy.

Regular eye assessment is an important part of diabetes care.

Sudden or severe visual changes require prompt medical attention.

Slow-Healing Wounds

Persistently high blood glucose can interfere with:

• circulation,
• immune function,
• and wound healing.

People with diabetes may therefore experience wounds that heal more slowly.

Foot wounds are particularly important because nerve damage may make injuries difficult to feel.

A persistent wound, especially on the foot, should not be ignored.

Frequent Infections

Diabetes can increase susceptibility to certain infections.

These can include:

• skin infections,
• urinary tract infections,
• and yeast infections.

Repeated infections do not necessarily mean someone has diabetes, but unexplained recurrent infections can be one reason to discuss blood glucose testing with a healthcare professional.

Does High Blood Pressure Mean You Have Diabetes?

No.

The old version of this article lists high blood pressure as a diabetes symptom.

That is misleading.

High blood pressure is not a typical symptom used to identify diabetes.

However, high blood pressure and type 2 diabetes frequently occur together and share several risk factors.

Having both conditions can significantly increase cardiovascular and kidney risks.

Managing blood pressure is therefore an important part of diabetes care.

Are Irregular Periods a Diabetes Symptom?

Irregular menstrual periods are not a standard symptom used to diagnose diabetes.

However, polycystic ovary syndrome (PCOS) can cause:

• irregular periods,
• excess facial or body hair,
• acne,
• and fertility problems.

PCOS is associated with insulin resistance and an increased risk of developing type 2 diabetes.

Someone with PCOS may therefore be advised to undergo appropriate metabolic screening.

Risk Factors for Type 2 Diabetes

Several factors can increase the likelihood of developing type 2 diabetes.

These include:

• family history of type 2 diabetes,
• overweight or obesity,
• carrying excess weight around the waist,
• physical inactivity,
• increasing age,
• previous gestational diabetes,
• PCOS,
• prediabetes,
• and certain other metabolic conditions.

Genetics also play an important role.

Diabetes, Ethnicity and Risk

Rates of type 2 diabetes vary among populations around the world.

Some ethnic populations develop type 2 diabetes more frequently or at younger ages.

These differences can reflect a complex combination of:

• genetics,
• socioeconomic conditions,
• access to healthcare,
• food environments,
• physical activity opportunities,
• and other environmental factors.

Ethnicity should therefore be considered as part of a broader health assessment rather than as an explanation on its own.

Does Obesity Cause Type 2 Diabetes?

Overweight and obesity are important risk factors for type 2 diabetes, but the relationship is not as simple as saying obesity automatically causes diabetes.

Many people with obesity never develop diabetes, while some people with type 2 diabetes are not overweight.

Risk is influenced by a combination of:

• genetics,
• insulin resistance,
• body-fat distribution,
• age,
• physical activity,
• and other metabolic factors.

People should receive evidence-based support rather than blame or stigma.

How Is Diabetes Diagnosed?

Diabetes is diagnosed using appropriate blood tests.

Common tests include:

• A1C (HbA1c),
• fasting plasma glucose,
• oral glucose tolerance testing,
• and random plasma glucose in certain situations.

A home blood glucose meter can help someone monitor known diabetes, but a home glucose meter alone should not be used to diagnose diabetes.

Diagnosis should be made using appropriate clinical testing.

What Is the A1C Test?

The A1C, also called HbA1c, measures the percentage of haemoglobin in the blood that has glucose attached to it.

It provides an estimate of average blood glucose over approximately the previous three months.

A1C can be useful for:

• diagnosing type 2 diabetes,
• identifying prediabetes,
• and monitoring diabetes.

However, it is not appropriate for every situation.

Understanding A1C Results

Common diagnostic thresholds used internationally include:

Normal: below 5.7%

Prediabetes: 5.7% to 6.4%

Diabetes: 6.5% or above

In someone without clear symptoms, an abnormal result generally requires confirmation according to appropriate clinical guidelines.

A1C may also be unreliable in certain circumstances, including some blood disorders, anaemias and situations affecting red blood cells.

Healthcare professionals may use other glucose tests when necessary.

Fasting Blood Glucose

A fasting plasma glucose test measures blood glucose after fasting, usually for at least eight hours.

Common diagnostic thresholds for non-pregnant adults are:

Normal: 99 mg/dL (5.5 mmol/L) or below

Prediabetes: 100–125 mg/dL (5.6–6.9 mmol/L)

Diabetes: 126 mg/dL (7.0 mmol/L) or above

Diagnosis usually requires confirmation unless the clinical circumstances clearly establish diabetes.

Different criteria apply during pregnancy.

What Complications Can Diabetes Cause?

Persistently high blood glucose can gradually damage blood vessels and nerves.

Possible long-term complications include:

• heart disease,
• stroke,
• kidney disease,
• diabetic retinopathy and vision loss,
• nerve damage,
• foot ulcers,
• lower-limb amputation,
• and dental and oral-health problems.

Diabetes is also associated with increased risk of some other health conditions.

Appropriate treatment can significantly reduce the risk of many complications.

Diabetes and Heart Disease

People with diabetes have an increased risk of cardiovascular disease.

Risk is influenced not only by blood glucose but also by:

• blood pressure,
• cholesterol,
• smoking,
• kidney health,
• body weight,
• and physical activity.

Comprehensive diabetes management therefore involves much more than simply monitoring sugar intake.

Diabetes and Kidney Disease

High blood glucose can damage the kidneys' filtering system over time.

Diabetes is a major cause of chronic kidney disease worldwide.

Kidney damage may initially produce no symptoms.

Routine testing can therefore include:

• kidney-function blood tests,
• and urine tests for albumin or protein.

Early identification allows treatment aimed at slowing further damage.

Diabetes and Nerve Damage

Long-term high blood glucose can damage nerves.

This is known as diabetic neuropathy.

Symptoms may include:

• numbness,
• tingling,
• burning,
• pain,
• or reduced sensation,

particularly in the feet and legs.

Reduced sensation increases the risk that injuries may go unnoticed.

Diabetes and Foot Health

People with diabetes should pay attention to foot health, particularly if they have:

• nerve damage,
• reduced circulation,
• previous ulcers,
• or foot deformities.

Seek medical care for:

• open wounds,
• spreading redness,
• swelling,
• discharge,
• blackened skin,
• or other signs of significant infection or tissue damage.

Early treatment can prevent serious complications.

Can Type 2 Diabetes Be Prevented?

Type 2 diabetes can often be prevented or delayed, particularly in people at increased risk.

WHO recommends lifestyle measures including:

• maintaining a healthy body weight,
• regular physical activity,
• healthy eating,
• and avoiding tobacco.

Prevention does not mean that every person who develops type 2 diabetes failed to live healthily.

Genetics and other factors remain important.

Physical Activity and Diabetes Prevention

Regular physical activity improves the body's sensitivity to insulin and supports cardiovascular and metabolic health.

WHO recommends that adults generally aim for at least 150 minutes of moderate-intensity physical activity each week, although individual ability and medical circumstances vary.

Activity can include:

• brisk walking,
• cycling,
• swimming,
• dancing,
• active recreation,
• and other forms of movement.

Strengthening activities are also valuable.

People who have been inactive or have significant health conditions may benefit from professional advice before beginning vigorous exercise.

Healthy Eating and Type 2 Diabetes

There is no single universal “diabetes prevention diet.”

A nutritious eating pattern generally emphasizes:

• vegetables,
• whole fruits,
• legumes,
• whole grains,
• nuts and seeds,
• healthy sources of protein,
• and unsaturated fats.

It can also help to limit:

• sugar-sweetened drinks,
• excessive free sugars,
• highly processed foods,
• and foods high in saturated or trans fats.

Portion sizes and total energy intake also matter for weight management.

Healthy eating should be adapted to culture, availability, affordability and individual health needs.

Does Eating Sugar Cause Diabetes?

Eating sugar does not directly cause type 1 diabetes.

For type 2 diabetes, the relationship is more complex.

Regular consumption of high-calorie foods and sugar-sweetened drinks can contribute to weight gain and metabolic risk, which can increase the likelihood of type 2 diabetes.

But type 2 diabetes develops through multiple interacting factors.

Simply eating a sugary food occasionally does not mean someone will develop diabetes.

Weight Loss and Diabetes Prevention

For people with overweight or obesity who are at increased risk of type 2 diabetes, modest and sustainable weight loss can significantly reduce risk.

Extreme dieting is unnecessary and often difficult to maintain.

A healthier approach usually combines:

• nutritious food,
• appropriate portions,
• physical activity,
• adequate sleep,
• and long-term behavioural changes.

Some people may also benefit from professional weight-management treatment.

Smoking and Diabetes

Tobacco use is associated with increased risk of type 2 diabetes and significantly increases cardiovascular risks.

For people who smoke, stopping is one of the most beneficial steps for overall health.

Avoiding tobacco also reduces risks of:

• heart disease,
• stroke,
• cancer,
• and lung disease.

How Is Diabetes Treated?

Treatment depends on the type of diabetes and individual circumstances.

It may involve:

• healthy eating,
• regular physical activity,
• weight management,
• blood glucose monitoring,
• medicines,
• insulin,
• blood-pressure management,
• cholesterol management,
• and regular screening for complications.

Treatment plans should be individualized.

Type 1 Diabetes Treatment

People with type 1 diabetes require insulin every day to survive.

Insulin may be delivered through:

• injections,
• insulin pens,
• or insulin pumps.

Continuous glucose monitors and other diabetes technologies can help many people manage glucose levels.

Stopping insulin in someone with type 1 diabetes can be life-threatening.

Type 2 Diabetes Treatment

Some people with type 2 diabetes can initially manage their condition through lifestyle changes.

Others require medication.

Treatment may include:

• metformin,
• other glucose-lowering tablets,
• injectable medicines,
• or insulin.

Modern diabetes medicines may also provide benefits for the heart, kidneys or body weight in appropriately selected patients.

The best treatment depends on the person's health and should be determined with a qualified healthcare professional.

Can Type 2 Diabetes Go Into Remission?

Some people with type 2 diabetes can achieve remission, particularly following substantial and sustained weight loss.

Remission generally means blood glucose remains below the diabetes diagnostic range for a defined period without glucose-lowering medication.

Remission is not the same as a guaranteed permanent cure.

Blood glucose can rise again, so ongoing health monitoring remains important.

Diabetes During Pregnancy

Pregnancy in someone with diabetes requires careful medical management.

High blood glucose during pregnancy can increase risks for both the pregnant person and baby.

People with:

• pre-existing type 1 diabetes,
• pre-existing type 2 diabetes,
• or gestational diabetes

may need additional monitoring and individualized glucose targets.

Medication requirements can also change during pregnancy.

What Is Low Blood Sugar?

Some diabetes treatments, particularly insulin and certain glucose-lowering medicines, can cause blood glucose to fall too low.

This is called hypoglycaemia.

Symptoms can include:

• shaking,
• sweating,
• hunger,
• dizziness,
• weakness,
• confusion,
• irritability,
• and difficulty concentrating.

Severe hypoglycaemia can cause:

• seizures,
• unconsciousness,
• or other medical emergencies.

People using medicines that can cause hypoglycaemia should receive individualized instructions on recognising and treating it.

What Is Diabetic Ketoacidosis?

Diabetic ketoacidosis (DKA) is a serious medical emergency caused by severe insulin deficiency.

It occurs most commonly in type 1 diabetes but can occur in other circumstances.

Warning signs may include:

• excessive thirst,
• frequent urination,
• nausea or vomiting,
• abdominal pain,
• deep or rapid breathing,
• dehydration,
• unusual tiredness,
• confusion,
• and sometimes fruity-smelling breath.

DKA requires urgent medical treatment.

It should never be managed solely through internet advice or home remedies.

When Should You Get Tested for Diabetes?

Discuss testing with a healthcare professional if you:

• have symptoms suggestive of diabetes,
• have been told you have prediabetes,
• have a strong family history,
• have overweight or obesity alongside other risk factors,
• have PCOS,
• previously had gestational diabetes,
• or have other recognized risk factors.

Testing recommendations vary according to age, pregnancy status, population risk and national guidelines.

When Should You Seek Urgent Medical Care?

Seek urgent medical care if someone with known or suspected diabetes develops:

• severe vomiting,
• significant dehydration,
• difficulty breathing,
• severe weakness,
• confusion,
• loss of consciousness,
• seizures,
• or symptoms suggesting diabetic ketoacidosis.

Severe hypoglycaemia that causes unconsciousness, seizures or inability to safely take glucose also requires emergency assistance.

Contact the appropriate emergency medical service where you live.

Living Well With Diabetes

A diabetes diagnosis does not mean that serious complications are inevitable.

Good long-term management can include:

• taking medicines as prescribed,
• monitoring glucose when appropriate,
• regular medical reviews,
• healthy eating,
• regular physical activity,
• avoiding tobacco,
• managing blood pressure,
• managing cholesterol,
• appropriate kidney tests,
• eye examinations,
• and foot care.

Treatment should be individualized rather than aiming for exactly the same glucose or A1C target in every person.

The Bottom Line

Diabetes occurs when blood glucose remains too high because the body does not produce enough insulin, produces no insulin, does not use insulin effectively, or experiences a combination of these problems.

The main forms are:

• type 1 diabetes,
• type 2 diabetes,
• and gestational diabetes.

Type 1 diabetes is an autoimmune disease and cannot currently be prevented.

Type 2 diabetes is the most common form and can often be prevented or delayed through healthy lifestyle changes, particularly in people at increased risk.

Gestational diabetes develops during pregnancy and requires appropriate monitoring and treatment.

Common diabetes symptoms include:

• excessive thirst,
• frequent urination,
• increased hunger,
• fatigue,
• unexplained weight loss,
• blurred vision,
• slow-healing wounds,
• and recurrent infections.

However, some people—especially those with type 2 diabetes—have few or no symptoms.

Blood testing is therefore essential for diagnosis.

Early diagnosis and effective management can substantially reduce the risk of damage to the heart, blood vessels, kidneys, eyes, nerves and feet.

Medical Disclaimer

This article provides general health information for an international audience and is not a substitute for individualized medical advice, diagnosis or treatment. Diabetes diagnosis requires appropriate clinical testing. Blood glucose and A1C targets vary according to the individual, pregnancy status, type of diabetes and other medical conditions. Never stop insulin or prescribed diabetes medication without appropriate medical advice. Seek urgent medical care for severe hypoglycaemia, suspected diabetic ketoacidosis, loss of consciousness or other serious symptoms.

Sources and Further Reading

World Health Organization — Diabetes

https://www.who.int/news-room/fact-sheets/detail/diabetes

World Health Organization — Diabetes Health Topic

https://www.who.int/health-topics/diabetes

National Institute of Diabetes and Digestive and Kidney Diseases — What Is Diabetes?

https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes

National Institute of Diabetes and Digestive and Kidney Diseases — Diabetes Symptoms and Causes

https://www.niddk.nih.gov/health-information/diabetes/overview/symptoms-causes

National Institute of Diabetes and Digestive and Kidney Diseases — Diabetes Tests and Diagnosis

https://www.niddk.nih.gov/health-information/diabetes/overview/tests-diagnosis

National Institute of Diabetes and Digestive and Kidney Diseases — A1C Test and Diabetes

https://www.niddk.nih.gov/health-information/diagnostic-tests/a1c-test

Centers for Disease Control and Prevention — Diabetes Risk Factors

https://www.cdc.gov/diabetes/risk-factors/

Centers for Disease Control and Prevention — Prediabetes and Type 2 Diabetes Prevention

https://www.cdc.gov/diabetes/prevention-type-2/prediabetes-prevent-type-2.html