Diabetes: Causes, Symptoms, Diagnosis, Complications, and Modern Treatment (Complete Guide)

Diabetes has become one of the defining medical challenges of the modern era. Over the past two decades, the global prevalence of the disease has more than quadrupled, transforming what was once considered a relatively uncommon condition into one of the most widespread chronic illnesses in the world. The World Health Organization now classifies diabetes among the most significant non-communicable disease burdens facing public health systems globally.

The numbers reflect more than statistics. Diabetes affects every major organ system in the body. It accelerates cardiovascular disease, damages kidneys, impairs nerves, and disrupts the normal functioning of blood vessels in ways that ripple through every aspect of long-term health. It is also one of the leading causes of preventable amputation worldwide, and a major contributor to dialysis-dependent kidney failure, premature blindness, and avoidable deaths from heart attack and stroke.

Yet diabetes is also one of the most preventable and treatable chronic diseases in medicine. Lifestyle changes can prevent the development of Type 2 diabetes in many at-risk individuals. Modern medications have transformed outcomes for those already diagnosed. New technologies provide unprecedented insight into daily blood sugar patterns. And the past decade has seen the emergence of medication classes, particularly GLP-1 receptor agonists and SGLT2 inhibitors, that have fundamentally changed what is achievable in diabetes care.

This guide explains how diabetes develops, who is at risk, how it is diagnosed, what complications it can cause, and how modern treatment approaches are reshaping outcomes for millions of people living with the disease.

What Is Diabetes?

Diabetes is a chronic metabolic disease characterized by elevated levels of glucose, the form of sugar that circulates in the blood. The elevation is not the disease itself but its defining feature. The underlying problem is a disruption in how the body produces or responds to insulin, the hormone responsible for regulating blood glucose.

In a healthy person, insulin allows glucose to move from the bloodstream into cells, where it provides energy for nearly every biological process. When this system breaks down, glucose accumulates in the blood while cells are deprived of the fuel they need. Over time, this dual problem of too much glucose outside cells and too little inside drives the wide-ranging consequences that define diabetes as a disease.

Diabetes is not a single condition. It is a family of disorders that share elevated blood glucose as a common feature but differ significantly in their causes, mechanisms, and management. Understanding the differences is essential to understanding how the disease is treated.

The Main Types of Diabetes

Two main types of diabetes account for the great majority of cases worldwide, with several less common types making up the remainder.

Type 1 Diabetes

Type 1 diabetes, sometimes still called juvenile diabetes because of its frequent onset in childhood and adolescence, is an autoimmune disease. The body's immune system mistakenly attacks and destroys the insulin-producing beta cells of the pancreas. Without these cells, the body cannot produce insulin at all.

People with Type 1 diabetes require lifelong insulin therapy from the moment of diagnosis. The condition is not caused by lifestyle factors and cannot be prevented through diet, exercise, or weight management. It is a relatively rare form of diabetes, accounting for roughly 5 to 10 percent of all cases globally.

Type 2 Diabetes

Type 2 diabetes is by far the more common form, accounting for over 90 percent of cases worldwide. It develops when the body's cells become resistant to the effects of insulin, while the pancreas, at first, increases insulin production to compensate. Over time, this compensation fails, insulin levels begin to fall, and blood glucose rises into the diabetic range.

Type 2 diabetes is closely linked to lifestyle and metabolic factors. Excess body weight, particularly abdominal fat, plays a central role in driving insulin resistance. Physical inactivity, diets high in refined carbohydrates and sugary drinks, and chronic inflammation all contribute. Genetics also play a meaningful role, but in most cases, lifestyle factors determine whether genetic risk translates into actual disease.

For a detailed comparison of the two main types, see Type 1 vs Type 2 Diabetes: Understanding the Key Differences.

Gestational Diabetes

Gestational diabetes develops during pregnancy in women who did not previously have diabetes. It usually resolves after delivery but identifies women at significantly increased risk of developing Type 2 diabetes later in life. It also has implications for the pregnancy itself, requiring careful management to protect both mother and baby.

For a full discussion of gestational diabetes, see Gestational Diabetes: Risks, Management, and What to Expect.

Other Forms

Less common forms of diabetes include LADA, latent autoimmune diabetes in adults, which behaves somewhat like a slower-developing form of Type 1, and MODY, maturity-onset diabetes of the young, a group of genetic conditions that cause diabetes in young people but follow different patterns from typical Type 1 or Type 2 disease.

Why Type 2 Diabetes Has Become So Common

The dramatic rise in Type 2 diabetes globally is not a mystery. It reflects a set of converging changes in how people eat, move, and live across most of the world.

Obesity

Excess body weight is the single most important driver of Type 2 diabetes. More than 80 percent of people diagnosed with Type 2 are overweight or obese at the time of diagnosis. Excess fat tissue, particularly around the abdomen, produces inflammatory molecules that interfere with insulin signaling and drive insulin resistance, the central abnormality of Type 2 diabetes.

Sedentary Lifestyle

Physical activity directly improves insulin sensitivity, allowing cells to use glucose more efficiently. The widespread shift toward sedentary work, sedentary leisure, and reduced incidental movement has removed much of the daily activity that historically protected against diabetes.

Diet

Diets high in refined carbohydrates, sugary drinks, and processed foods drive both weight gain and direct metabolic stress on the system that regulates blood sugar. Sugary beverages in particular have been associated with diabetes risk in study after study, independent of overall calorie intake.

Genetics and Family History

Genetic factors play a significant role in determining who develops Type 2 diabetes when exposed to lifestyle risk factors. Family history is one of the strongest individual predictors of risk, and certain ethnic populations carry meaningfully higher genetic susceptibility than others.

Socioeconomic Factors

Access to healthy food, opportunities for physical activity, and exposure to diabetes prevention information vary significantly by socioeconomic status. Communities with fewer resources often experience disproportionately high diabetes rates, reflecting the broader social determinants of metabolic health.

Recognizing the Symptoms

In its early stages, particularly for Type 2 diabetes, the disease can develop silently. Many people live with elevated blood sugar for years before symptoms become noticeable, and the condition is often diagnosed incidentally on routine bloodwork. When symptoms do appear, they reflect the body's response to chronically elevated glucose levels.

The most common symptoms include excessive thirst and frequent urination, which occur because the kidneys attempt to flush excess glucose from the body. Persistent fatigue is common, reflecting the inability of cells to use glucose effectively for energy. Unexplained weight loss can occur, particularly in Type 1 diabetes. Blurred vision, slow-healing wounds, and recurrent infections, particularly skin and urinary infections, are also common.

In Type 1 diabetes, symptoms typically develop rapidly over days to weeks and can be severe enough to bring a person to medical attention quickly. In Type 2 diabetes, symptoms often develop gradually and may be mild enough to be ignored or attributed to other causes for long periods of time.

This silent progression is one of the reasons routine screening matters, particularly in adults with risk factors. Many cases of Type 2 diabetes are diagnosed only after complications have already begun to develop.

How Diabetes Is Diagnosed

The diagnosis of diabetes is based on specific blood test results that reflect how the body is handling glucose. Three main tests are used.

Fasting Plasma Glucose

A fasting plasma glucose test measures blood sugar after at least eight hours without food. A fasting glucose level of 126 milligrams per deciliter or higher, confirmed on repeat testing, establishes the diagnosis of diabetes.

Hemoglobin A1c

The hemoglobin A1c test, often called HbA1c, reflects the average blood glucose level over the previous two to three months. It is performed without fasting and is not influenced by the time of day or recent meals. A hemoglobin A1c of 6.5 percent or higher confirms diabetes. This test has become increasingly central to diabetes diagnosis and is widely used because of its convenience, stability, and strong predictive relationship to long-term complications.

Oral Glucose Tolerance Test

The oral glucose tolerance test, often abbreviated OGTT, involves drinking a standardized glucose solution and measuring blood glucose levels at intervals over the next two hours. It is more cumbersome than the other tests but provides the most detailed information about how the body handles a glucose challenge. A two-hour glucose level of 200 milligrams per deciliter or higher on the OGTT establishes diabetes.

For a more detailed discussion of testing, see .

The Complications of Diabetes

Diabetes is best understood not as a single disease but as a chronic metabolic condition that gradually damages multiple organ systems. The complications are where much of the morbidity and mortality of diabetes originates.

Cardiovascular Disease

Diabetes is one of the most powerful cardiovascular risk factors. People with diabetes are two to four times more likely to have a heart attack or stroke than people without diabetes. This elevated risk reflects several mechanisms: diabetes accelerates atherosclerosis, promotes blood clotting, damages the function of blood vessels, and promotes inflammation throughout the cardiovascular system.

Diabetes-related heart disease often presents differently than in people without diabetes. Heart attacks can occur with minimal or no warning symptoms, a phenomenon sometimes called silent ischemia. Heart failure is also more common in people with diabetes, and it can develop through mechanisms independent of atherosclerotic coronary disease.

For more on this topic, see Diabetes and Heart Disease: The Cardiovascular Connection.

Kidney Disease

Diabetes is the leading cause of kidney failure requiring dialysis in the developed world. Over time, sustained hyperglycemia damages the delicate filtration structures of the kidney, gradually reducing the kidney's ability to filter waste and maintain fluid balance.

Diabetic kidney disease often progresses silently. Proteins in the urine may be the first detectable sign, present long before kidney function is significantly impaired. Once kidney function begins to decline, the process often accelerates. Regular screening with urine protein and serum creatinine or estimated glomerular filtration rate is central to early detection and intervention.

For more on kidney disease and diabetes, see Diabetic Kidney Disease: How to Protect Your Kidneys.

Eye Disease

Diabetic retinopathy, damage to the blood vessels in the retina, is the leading cause of preventable blindness in working-age adults in developed countries. The damage begins with leakage of fluid and blood from damaged vessels, progressing in more advanced cases to growth of new abnormal blood vessels that can detach the retina.

In its early stages, diabetic retinopathy causes no symptoms. By the time vision problems appear, significant damage has often already occurred. Regular dilated eye examinations are essential for early detection, and modern treatments, including laser therapy and injected medications, can prevent progression in many cases when applied early.

Other forms of eye disease are also more common in people with diabetes, including cataracts and glaucoma.

For more on this complication, see .

Nerve Damage

Diabetic neuropathy, nerve damage caused by sustained hyperglycemia, can affect any part of the peripheral nervous system. The most common form is distal sensorimotor neuropathy, which affects the longest nerves first, typically producing numbness and tingling in the feet and lower legs.

Other forms of diabetic neuropathy affect the autonomic nervous system, causing problems with blood pressure regulation, heart rate, sweating, digestion, and sexual function. Some forms are painful, while others impair sensation, creating risk of injury that goes unnoticed.

Neuropathy is one of the most common complications of diabetes, affecting a substantial proportion of people with the disease. Once established, it is often irreversible, which makes prevention through good glucose control particularly important.

For more on this complication, see Diabetic Neuropathy and the Diabetic Foot: Prevention and Care.

Foot Problems

The combination of sensory neuropathy and vascular disease creates particular risk for the feet. Sores develop, sensation is impaired, and the person does not feel the injury. At the same time, blood flow to the feet is reduced, impairing healing. Small injuries progress to larger ones, infections take hold, and sometimes amputation becomes necessary.

Foot ulcers and amputations represent one of the most visible and consequential complications of poorly controlled diabetes. Modern foot care, including regular examination by healthcare providers trained in diabetic foot disease, can prevent the great majority of amputations.

For more on foot care, see Diabetic Neuropathy and the Diabetic Foot: Prevention and Care.

Modern Treatment of Diabetes

Modern diabetes treatment has been transformed by new medication classes and by a fundamental shift toward earlier, more intensive intervention.

Treatment Goals

The goal of diabetes treatment is to maintain blood glucose in a range that prevents both the acute complications of hyperglycemia and the chronic complications that develop from years of sustained elevation. In most patients, a hemoglobin A1c target of 7 percent or slightly below is reasonable, though individualized targets are often appropriate based on age, health status, and ability to tolerate hypoglycemia.

Beyond glucose control, diabetes treatment addresses the cardiovascular and metabolic consequences of the disease. Management of blood pressure, cholesterol, and other cardiovascular risk factors is as important as glucose control in determining long-term outcomes.

Lifestyle Intervention

Lifestyle change remains fundamental. Weight loss in overweight patients has been shown to substantially reduce insulin resistance and even to produce remission of Type 2 diabetes in some individuals. Regular physical activity improves insulin sensitivity and produces broader cardiovascular benefits. Dietary change toward less refined carbohydrates and processed foods and more vegetables, whole grains, and lean protein reduces both weight and blood glucose directly.

For patients motivated and able to implement substantial lifestyle changes, the impact on disease trajectory can be dramatic. Some patients achieve normal glucose levels through lifestyle change alone, without any medications. For others, lifestyle change makes medications more effective and allows lower doses to be used.

For more on this approach, see .

Medications for Type 2 Diabetes

When lifestyle change alone is insufficient, several classes of medication are available.

Metformin remains the first-line medication for most patients with Type 2 diabetes. It works primarily by improving insulin sensitivity and reducing hepatic glucose production. It is effective, well-tolerated, relatively inexpensive, and has been in use long enough that its safety profile is well-established.

Sulfonylureas and meglitinides stimulate insulin secretion from the pancreas. These are older medications that can be effective but carry increased risk of hypoglycemia and weight gain, which has limited their role in modern practice.

Thiazolidinediones improve insulin sensitivity and have cardiovascular and kidney-protective effects in some populations, but they carry the downside of weight gain and other side effects that have limited their role.

DPP-4 inhibitors block the breakdown of a hormone that stimulates insulin secretion. They are weight-neutral and generally well-tolerated, but their glucose-lowering effect is modest.

SGLT2 inhibitors are among the most important advances in recent diabetes care. These medications work by increasing glucose excretion through the urine. Beyond their glucose-lowering effect, they provide remarkable benefits: they reduce hospitalization for heart failure, they slow the progression of kidney disease, and in some cases they reduce cardiovascular mortality. Their benefits extend beyond glucose control and have made them a preferred option in patients with heart failure or kidney disease, even if glucose control is not the primary goal.

For more on SGLT2 inhibitors, see SGLT2 Inhibitors: A New Class of Diabetes Medication.

GLP-1 Receptor Agonists

GLP-1 receptor agonists have transformed Type 2 diabetes care, both for glucose control and for weight loss. These medications work by mimicking a hormone that stimulates insulin secretion and suppresses appetite. They are injected once weekly (or in some formulations more frequently) and produce effective glucose lowering and meaningful weight loss in many patients.

Beyond their metabolic effects, GLP-1 receptor agonists have been shown to reduce cardiovascular events and mortality in patients at high cardiovascular risk. For patients with Type 2 diabetes and obesity, they have become a cornerstone of treatment.

The main limitations are cost (they are expensive), gastrointestinal side effects (nausea is common early on), and access (supply has been limited due to high demand). But for appropriate patients, their benefits are substantial.

For more on this class, see GLP-1 Medications: How Ozempic, Wegovy, and Mounjaro Work.

Treatment of Type 1 Diabetes

Type 1 diabetes requires insulin from the moment of diagnosis. Multiple insulin formulations are available, including rapid-acting, intermediate-acting, and long-acting insulins. Most patients use multiple daily injections or an insulin pump to achieve good glucose control.

Modern insulin pumps and continuous glucose monitors have transformed the practical management of Type 1 diabetes, allowing closer matching of insulin dose to actual glucose needs and providing moment-to-moment information about glucose trends.

Despite excellent insulin and technology, maintaining normal or near-normal glucose levels in Type 1 diabetes is challenging. Hypoglycemia remains a significant concern, particularly in patients attempting tight glucose control.

For more on Type 1 diabetes management, see .

The Impact of Continuous Glucose Monitoring

Continuous glucose monitors, devices that measure glucose levels continuously throughout the day and night, have become transformative tools in diabetes management. They provide real-time glucose information, alert users to high and low glucose levels, and allow visualization of glucose trends.

For people with Type 1 diabetes, continuous glucose monitors have become essentially standard of care. For people with Type 2 diabetes on insulin, they are increasingly used. Some people with Type 2 diabetes not on insulin also use them to better understand how specific foods and activities affect their glucose.

The detailed glucose information that continuous monitors provide allows much more precise insulin dosing and identifies patterns that would not be obvious from once-daily or occasional glucose checks.

For more on this technology, see Continuous Glucose Monitors (CGM): Modern Technology for Diabetes Management.

Living With Diabetes

Diabetes is a chronic condition that will affect some aspect of daily life for everyone who has it. The burden varies widely depending on how successfully glucose is controlled, what complications have developed, and the individual's access to care and support.

Most people with diabetes, particularly those with good glucose control and access to modern treatment, can live normal lifespans and normal quality of life. Regular medical monitoring, consistent medication use, appropriate dietary choices, and regular physical activity form the foundation.

For people with Type 1 diabetes, the requirement for lifelong insulin therapy and frequent glucose monitoring is an ongoing reality. But modern technologies have made this considerably less burdensome than in previous eras.

For people with Type 2 diabetes, the opportunity for prevention or remission through lifestyle change is real, particularly early in the disease course. Even those requiring medications often find them manageable once started.

The key to living well with diabetes is early diagnosis, prompt initiation of appropriate treatment, regular monitoring, and attention to the broader cardiovascular risk factors that diabetes carries.

For more on living well with diabetes, see .

Diabetes Prevention

One of the most important messages about diabetes is that Type 2 diabetes is largely preventable. Multiple large clinical trials have demonstrated that lifestyle intervention—weight loss combined with regular physical activity—can prevent the development of Type 2 diabetes in people at high risk.

The effect is substantial. The Diabetes Prevention Program, a landmark trial in the United States, showed that intensive lifestyle intervention reduced the incidence of Type 2 diabetes by 58 percent over a three-year period, with benefit sustained for years beyond the trial.

Metformin also prevents or delays the development of Type 2 diabetes in at-risk individuals, though the effect is smaller than that of intensive lifestyle intervention.

For high-risk individuals, including those who are overweight with family history of diabetes or those with impaired glucose tolerance, screening and early intervention can meaningfully reduce the risk of developing the disease.

For more on prevention, see .

When to See a Specialist

While many aspects of diabetes care can be managed in primary care, specialist evaluation by an endocrinologist can be valuable in several situations.

These include difficult-to-control glucose levels despite appropriate medical management, complicated medical situations with multiple comorbid conditions, consideration of new treatment approaches or technologies, complex pregnancies with pregestational or gestational diabetes, and initial evaluation of Type 1 diabetes.

Specialist care is also valuable in optimizing medication regimens in patients with Type 2 diabetes and heart failure or kidney disease, where the choice of agent matters substantially for outcomes beyond glucose control.

Conclusion

Diabetes has become one of the most consequential health challenges of our time. Its prevalence continues to rise, and its complications affect millions of people worldwide. The disease shortens lives, impairs quality of life, and consumes vast resources in healthcare systems globally.

Yet the modern era has also brought unprecedented opportunity. Diabetes is preventable in many at-risk individuals through lifestyle change. When it does develop, it is diagnosable early, treatable effectively, and manageable to the point where many patients live normal lifespans with good quality of life.

New medications, particularly GLP-1 receptor agonists and SGLT2 inhibitors, have transformed outcomes. New technologies, particularly continuous glucose monitoring, have changed the practical reality of living with diabetes. And the growing recognition that earlier intervention produces better long-term outcomes has shifted the paradigm of diabetes care toward more aggressive and earlier treatment strategies.

The practical message is clear. Diabetes should not be ignored or minimized. Screening matters. Early intervention matters. Consistent treatment matters. And for the millions of people diagnosed with diabetes today, modern medicine offers meaningful tools to prevent complications and to live full, active lives.

For more on diabetes and its complications, see and . For more on specific complications, see Diabetes and Heart Disease: The Cardiovascular Connection, Diabetic Kidney Disease: How to Protect Your Kidneys, and Diabetic Neuropathy and the Diabetic Foot: Prevention and Care.

About the Author

Prof. Jacob Giris

MD, DSc

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Clinical and research focus is the autonomic nervous system — how it regulates blood pressure, heart rate, and circulation, and what happens when this regulation breaks down. Patients are treated for Postural Tachycardia Syndrome (POTS), orthostatic intolerance, and related conditions, alongside ongoing research into the interactions between pain and the autonomic system.

Training in internal medicine was completed at Rambam Medical Center in Haifa, followed by an International MERCK Fellowship in clinical pharmacology at Vanderbilt University, and a DSc in pharmacology and physiology at the Technion — Israel Institute of Technology.

Current roles include Head of Internal Medicine Department F at Tel Aviv Sourasky Medical Center (Ichilov), Director of the Joseph Recanati Autonomic Dysfunction Center, and Professor of Medicine, Physiology and Pharmacology at the Tel Aviv University Faculty of Medicine. Published work includes more than 70 peer-reviewed papers with over 9,000 citations.

Senior medical advisor to Lema'anchem on a volunteer basis, helping patients navigate complex diagnoses and access world-class medical expertise.

Editorial Note

This article was reviewed and formatted by the MED.COM editorial process to align with international clinical standards.

Medical Disclaimer

This content is provided for informational and educational purposes only. It does not constitute medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare professional regarding any medical condition.