Diabetes Mellitus

Diabetes mellitus is chronic high blood sugar that, untreated, damages kidneys, eyes, nerves, and blood vessels. Affects 38 million Americans.

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Minimal editorial imagery representing glucose monitoring and daily diabetes management.

By Kaveh Samani, MD · Internal Medicine PhysicianReviewed May 9, 20262 min read

Key takeaways

Diabetes mellitus is chronic high blood sugar that, untreated, damages the kidneys, eyes, nerves, and blood vessels — and it often has no early symptoms, especially in type 2.
Type 1 is autoimmune and requires lifelong insulin; type 2, the most common, involves insulin resistance and is strongly influenced by weight, activity, and genetics; gestational diabetes occurs in pregnancy.
Most adults aim for an A1C below 7%, but targets are individualized — and management has shifted from glucose-only goals toward preventing cardiovascular death, heart failure, and kidney failure.
Medication is now chosen by your comorbidities, not glucose alone: with heart disease, heart failure, or kidney disease, an SGLT2 inhibitor and/or GLP-1 receptor agonist is recommended for organ protection regardless of A1C.
Lifestyle remains foundational — nutrition, activity, and weight management improve insulin sensitivity — and coordinated care to control blood pressure and protect the kidneys is central to preventing complications.

Understanding Diabetes Mellitus

Diabetes Mellitus is a chronic disease that affects the way your body processes glucose (blood sugar).

Diabetes can be classified into three types:

Type 1 Diabetes: A condition in which the immune system attacks the insulin-producing pancreatic cells. It is usually diagnosed in childhood or young adulthood, and requires insulin therapy for life.
Type 2 Diabetes: The most common type of diabetes, in which the body is resistant to insulin and/or does not produce enough. It is often related to lifestyle factors like diet, weight, and physical activity.
Gestational Diabetes: A temporary form of diabetes which occurs during pregnancy. It increases the risk for Type 2 diabetes in later life.

Common Symptoms of Diabetes

Some people have diabetes without even realizing it. Early detection of diabetes symptoms can be a game changer:

Frequent urination, particularly at night
Extreme thirst and hunger
Unexpected weight loss
Fatigue and irritability
Blurred vision
Slow-healing wounds
Numbness or tingling in the fingers and toes
Infections of the gums, skin, or vaginal area

It's vital to visit a doctor if you or someone close to you experiences any of these symptoms.

What Causes Diabetes?

Type 2 diabetes can be influenced by lifestyle and genetic factors:

Obesity: Increased insulin resistance due to excess weight, particularly around the abdomen.
Sedentary Lifestyle: An inactive lifestyle can reduce the body's ability to regulate blood glucose.
Poor Diet: Consuming processed foods, sugary beverages, and unhealthy fats increases the risk.
Family History: A close relative who has diabetes increases your chances of getting it.
Age: As you age, the risk of Type 2 diabetes increases.
High Blood Pressure and Cholesterol: These conditions have a close relationship with insulin resistance and diabetes.

Managing and Treating Diabetes

Lifestyle Changes

Healthy Eating: Focus on whole foods, healthy fats, and carbohydrates rich in fiber. Avoid sugary and processed foods.
Exercise Regularly: Regular physical activity improves insulin sensitivity and helps regulate blood glucose levels.
Weight Control: Maintaining an ideal weight can reduce the risk of complications.
Blood Sugar Monitoring: Tracking blood sugar levels can help you adjust your diet, exercise, and medications as necessary.

Insulin Therapy and Medications

Oral Medications: Metformin, for Type 2 diabetes patients, helps regulate blood sugar.
Insulin Therapy: Essential for Type 1 diabetes, and sometimes advanced Type 2 diabetes.
Other Medicines: Certain drugs can help the body produce more insulin, or use it better.

Avoiding Complications

Diabetes can increase the risk of developing other health issues, including heart disease, kidney problems, nerve damage, and vision loss. A healthy lifestyle and regular checkups can help to prevent complications.

Number to know	Goal for most adults
A1c	Below 7%
Blood pressure	Below 130/80 mmHg
Fasting glucose	80–130 mg/dL

Signs & symptoms

Signs and symptoms to watch for

Often no symptoms early, especially in type 2 diabetes
Increased thirst
Frequent urination
Increased hunger
Unexplained weight loss
Fatigue
Blurred vision
Slow-healing sores or cuts
Frequent infections
Tingling or numbness in the hands or feet

When to see a specialist

Should you see a specialist?

Schedule an evaluation if you have any classic diabetes symptoms, are over 45 with risk factors, are overweight with one or more risk factors, have an A1C in the pre-diabetes range, or were recently diagnosed and need help establishing a management plan.

Frequently asked

Diabetes Mellitus questions, answered

What are the early warning signs of diabetes?

Increased thirst and urination, unexplained weight loss, fatigue, blurred vision, and slow-healing cuts are common early signs. Many people, though, have no symptoms early on.

What is a normal blood sugar and A1c?

For most adults, an A1c below 5.7% is normal and 6.5% or higher indicates diabetes; a common treatment goal is an A1c below 7%. Your doctor sets the target that fits you.

Can type 2 diabetes be reversed?

It can often be put into remission, especially early, with significant weight loss and lifestyle change. Even when not reversed, it can be well controlled to prevent complications.

How does diabetes affect the kidneys?

High blood sugar over time damages the kidney's filters, and diabetes is the leading cause of kidney failure. A yearly urine test catches this early, when it's most treatable.

What are the long-term complications of diabetes?

Poorly controlled diabetes can damage the kidneys, eyes, nerves, heart, and blood vessels. Keeping blood sugar, blood pressure, and cholesterol in range prevents most of these.

Sources

References

American Diabetes Association Professional Practice Committee. 9. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes—2025. Diabetes Care 2025;48(Suppl 1):S181–S206 — https://diabetesjournals.org/care/article/48/Supplement_1/S181/157569/
American Diabetes Association. Standards of Care in Diabetes—2026 (Pharmacologic Approaches to Glycemic Treatment). Diabetes Care 2026;49(Suppl 1):S183 — https://diabetesjournals.org/care/article/49/Supplement_1/S183/163934/
ElSayed NA, et al. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes—2025. Diabetes Care 2025;48(Suppl 1) — https://diabetesjournals.org/care/issue/48/Supplement_1
Centers for Disease Control and Prevention: About Diabetes — https://www.cdc.gov/diabetes/about/index.html
National Institute of Diabetes and Digestive and Kidney Diseases: Diabetes — https://www.niddk.nih.gov/health-information/diabetes
American Diabetes Association: Diagnosis — https://diabetes.org/about-diabetes/diagnosis

SpecialtyInternal MedicineICD-10 codeE11.9Associated anatomyPancreas, beta cells, blood vessels, kidneys, eyes, peripheral nerves

Also called Diabetes, DM, Type 1 Diabetes, Type 2 Diabetes, Hyperglycemia, T2DM, T1DM

This page is for general education and is not a substitute for medical advice from your physician. Contact a Remix Medical clinician about your specific situation.

Updated May 9, 2026. Medically reviewed by Kaveh Samani, MD.