Diabetes Mellitus: Types, Causes, Symptoms, Risk Factors, and 2026 Guidelines

"Learn about diabetes mellitus, its symptoms, causes, treatment, prevention, and key updates in the ADA 2026 Guidelines."

September 27, 2026

Illustration. Diabetes mellitus and blood sugar level testing using a glucometer.

Diabetes mellitus is a condition in which blood sugar, or glucose, levels become too high because the body's ability to regulate glucose is impaired. The condition is closely linked to insulin, a hormone that helps glucose move from the bloodstream into cells where it can be used for energy.

Diabetes is not simply caused by eating too much sugar. Different types of diabetes have different mechanisms and risk factors, which means their management may also vary.

What Is Diabetes Mellitus?

Under normal conditions, the body has mechanisms that help keep blood glucose levels within a healthy range. Insulin plays an important role by helping glucose enter the body's cells.

In people with diabetes, this process is disrupted. In type 1 diabetes, insulin-producing pancreatic cells are damaged. In type 2 diabetes, the body may develop insulin resistance, or the pancreas may not produce enough insulin.

Because the underlying mechanisms differ, diabetes management needs to be tailored to each person's condition. Treatment may include dietary changes, physical activity, medication, and insulin therapy.

Type 1 and Type 2 Diabetes

Type 1 Diabetes

Type 1 diabetes is often associated with younger people, but it can also develop in adults.

In type 1 diabetes, the pancreatic cells responsible for producing insulin are damaged. The source material associates this condition with mechanisms such as autoimmunity, in which the immune system attacks pancreatic cells, as well as pancreatic damage caused by certain factors such as injury or surgery.

Because the body no longer produces enough insulin, people with type 1 diabetes require insulin from outside the body.

Type 2 Diabetes

Type 2 diabetes is the more common form of diabetes. In this condition, the pancreas may still produce insulin, but the amount may not be sufficient, or the body may not respond effectively to insulin.

The condition in which the body does not respond effectively to insulin is known as insulin resistance. Some people with type 2 diabetes can manage the condition through dietary and lifestyle changes, while others may require medication or insulin.

Other Conditions That Use the Term Diabetes

The term diabetes does not always refer to diabetes mellitus.

One example is diabetes insipidus, which is different from diabetes mellitus. This condition primarily involves the body's water-regulation system and may be associated with the kidneys or pituitary gland. Symptoms can include frequent urination and excessive thirst.

The source material also discusses MODY (Maturity-Onset Diabetes of the Young). This condition is associated with a change or mutation in a single gene that can be inherited and is different from both type 1 and type 2 diabetes.

Who Is at Risk of Developing Diabetes?

Several factors can increase the risk of diabetes, particularly type 2 diabetes.

According to the source material, these factors include:

Being overweight.
Low physical activity or a sedentary lifestyle.
Being over 35 years old.
Having a family history of diabetes.
Having experienced gestational diabetes during pregnancy.

Family history can play a role in both type 1 and type 2 diabetes, although the relationship and underlying mechanisms differ.

Diabetes is also not contagious. It cannot be transmitted through contact with another person because it is not caused by pathogens such as viruses or bacteria.

Do High Blood Pressure and Stress Cause Diabetes?

The source material discusses high blood pressure and stress as conditions that may be associated with diabetes.

People with high blood pressure are described as being statistically more likely to develop diabetes than people with normal blood pressure. However, this statistical association does not directly prove that high blood pressure causes diabetes.

The same applies to stress. Stress may be associated with diabetes, but the source material does not establish it as a direct proven cause.

Diabetes should therefore be understood as a condition involving multiple interconnected factors rather than a disease caused by one factor alone.

Diabetes Symptoms to Watch For

Diabetes symptoms can vary among infants, children, and adults.

In adults, symptoms that may need attention include unexplained weight loss, frequent thirst, frequent urination, and tingling in the hands and feet.

In children, symptoms may include excessive thirst, frequent urination, weight loss despite increased appetite, fatigue, behavioral changes, blurred vision, recurrent fungal infections, and tingling sensations.

In infants, signs mentioned in the source material include increased sleepiness or weakness, excessive hunger, slow-healing wounds, and certain conditions associated with excessively high or low blood glucose levels.

However, symptoms alone are not enough to confirm diabetes. Other medical conditions can cause similar symptoms, so medical testing is needed to determine the underlying cause.

How Is Diabetes Treated?

Diabetes treatment depends on the type of diabetes and each person's individual condition.

Insulin

Insulin is an important part of treatment for type 1 diabetes because the body no longer produces enough insulin.

Insulin can be administered through injections. The source material also discusses insulin pumps as another option for delivering insulin.

For type 2 diabetes, the need for insulin varies from person to person. Some people may require insulin, while others may manage their condition through lifestyle changes and medication.

Diabetes Medications

Metformin is one of the medications discussed in the source material. It works partly by reducing glucose production by the liver and improving the body's response to insulin.

The material also discusses medications such as glipizide and glimepiride, which work by increasing insulin production by the pancreas. Another group, known as DPP-4 inhibitors, affects hormonal mechanisms involved in blood glucose regulation.

Diet and Physical Activity

Diet and physical activity are also important components of diabetes management.

Regular physical activity can help maintain overall health and body weight. Meanwhile, an appropriate diet can help keep blood glucose levels under control.

The source material also discusses natural substances and alternative approaches such as stevia, magnesium, cinnamon, ginseng, chromium, and acupuncture. However, their inclusion in the discussion does not mean that all of these approaches have been proven effective as diabetes treatments.

Natural products or supplements should therefore not be used to replace medication prescribed by a doctor.

Steps to Reduce the Risk of Diabetes

The source material describes type 2 diabetes as the form of diabetes with the greatest potential for prevention.

Some habits to consider include maintaining a healthy eating pattern, engaging in regular physical activity, maintaining a healthy weight, and paying attention to blood pressure.

The material also discusses plant-based foods, magnesium sources such as black beans, spinach, and almonds, as well as stevia as a low- or zero-calorie sweetener. However, some claims about specific foods are presented as possibilities or findings from particular sources rather than definitive evidence that these foods can prevent diabetes.

Stress management is also discussed as part of a healthy lifestyle, although the material does not establish a definite cause-and-effect relationship between stress and diabetes.

What Is New in the 2026 Diabetes Guidelines?

The American Diabetes Association (ADA) updated its Standards of Care in Diabetes 2026, a comprehensive reference for clinicians, researchers, policymakers, and other stakeholders involved in diabetes care.

The 2026 update covers a range of areas, including diabetes diagnosis and classification, complication prevention, blood glucose management, diabetes technology, obesity treatment, medications, cardiovascular and kidney disease, and diabetes care in hospitalized patients.

Type 1 Diabetes Monitoring

The ADA added recommendations concerning monitoring individuals with confirmed positive results for certain autoimmune antibodies, including IA-2.

The guidelines also strengthen glucose monitoring for people receiving repeated or long-term glucocorticoid therapy and patients starting certain cancer treatments.

Diabetes Technology

The 2026 update also addresses diabetes technology, including automated insulin delivery (AID) systems and continuous insulin therapy.

According to the source material, certain requirements such as C-peptide testing, the presence of islet autoantibodies, or the duration of insulin therapy are not required before using these technologies.

Obesity and Diabetes Treatment

The ADA updated its recommendations on obesity treatment for people with diabetes. Treatment doses and adjustments should be individualized based on effectiveness, benefits, and tolerability.

For people with type 1 diabetes who have obesity, GLP-1 receptor agonist-based therapy and metabolic surgery are described as options that may be considered.

Diabetes and Kidney Disease

For people with type 2 diabetes and chronic kidney disease, the ADA update includes recommendations concerning the combined use of SGLT2 inhibitors and nsMRA in certain circumstances.

The source also mentions the use of SGLT2 inhibitors in patients who are not undergoing dialysis to help reduce the risk of chronic kidney disease progression and provide cardiovascular benefits.

Diabetes Management During Surgery

The 2026 guidelines also address diabetes management in patients undergoing elective surgery.

According to the source material, the HbA1c target during the three months before elective surgery is less than 8%. Alternatives mentioned include a GMI below 8% over a 14-day period or a time in range greater than 50%.

Around the time of surgery, the blood glucose target mentioned is 100–180 mg/dL.

Diabetes Requires Individualized Management

Diabetes is not the same condition for every person. Type 1 diabetes, type 2 diabetes, diabetes insipidus, and MODY have different characteristics and therefore cannot be managed in exactly the same way.

The 2026 Standards of Care in Diabetes update also demonstrates that diabetes management extends beyond blood glucose control. It includes obesity, diabetes technology, cardiovascular and kidney health, medications, and the management of patients during hospitalization.

For this reason, diagnosis and treatment choices should be tailored to each patient's condition and evaluated by healthcare professionals. Overall, the source material emphasizes lifestyle changes, ongoing monitoring, appropriate treatment, and consultation with healthcare professionals as important components of diabetes management.