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Diabetes Mellitus

Diabetes Mellitus: Understanding the Causes, Pathophysiology, Symptoms, Diagnosis, and Treatment Options

Diabetes mellitus is a chronic metabolic disorder characterized by high blood glucose levels (hyperglycemia) due to defects in insulin secretion, insulin action, or both. Insulin is a hormone produced by the pancreas that regulates the absorption and utilization of glucose in the body.

Diabetes mellitus is a significant public health concern worldwide, with an increasing prevalence in recent years. According to the International Diabetes Federation, the global prevalence of diabetes in adults (aged 20-79 years) was estimated to be 9.3% in 2019, with around 463 million people affected.


The prevalence of diabetes varies among different countries and regions, with the highest prevalence observed in low- and middle-income countries. In 2019, the countries with the highest number of people with diabetes were China (116 million), India (77 million), and the United States (34 million).

The incidence of diabetes is also increasing, particularly type 2 diabetes, which accounts for 90-95% of all diabetes cases. Risk factors for developing diabetes include obesity, physical inactivity, unhealthy diet, family history, age, ethnicity, and low socioeconomic status.

If left uncontrolled, diabetes can lead to several complications, such as cardiovascular disease, kidney disease, neuropathy, retinopathy, and amputations. Therefore, prevention, early detection, and management of diabetes are essential to reduce the burden of this disease on individuals and society.

Classification of Diabetes Mellitus

Diabetes mellitus can be classified into several types based on their underlying causes and clinical characteristics. The most common types of diabetes mellitus are:

Type 1 diabetes mellitus: 

This type of diabetes is characterized by an autoimmune destruction of the pancreatic beta cells that produce insulin. It usually presents in childhood or adolescence, and requires lifelong insulin therapy for management.

Type 2 diabetes mellitus: 

This type of diabetes is the most common form and is caused by a combination of insulin resistance and inadequate insulin secretion by the pancreas. It is usually diagnosed in adults, but is increasingly being seen in children and adolescents due to rising obesity rates.

Gestational diabetes mellitus: 

This type of diabetes develops during pregnancy and usually resolves after delivery. Women with gestational diabetes have a higher risk of developing type 2 diabetes later in life.


The etiopathogenesis (cause and development) of diabetes mellitus varies for type 1 and type 2 diabetes.

Type 1 diabetes:

Type 1 diabetes is caused by autoimmune destruction of pancreatic beta cells, which produce insulin. The exact cause of this autoimmune reaction is not known, but genetic and environmental factors may play a role. It is believed that certain viruses or other environmental factors may trigger an autoimmune response in genetically susceptible individuals, leading to destruction of beta cells and subsequent insulin deficiency. As a result, individuals with type 1 diabetes require lifelong insulin replacement therapy.

Type 2 diabetes:

Type 2 diabetes is caused by a combination of genetic and environmental factors. Insulin resistance, a condition in which cells become less responsive to the effects of insulin, is the primary defect that leads to the development of type 2 diabetes. Over time, the pancreas may also become unable to produce enough insulin to compensate for insulin resistance. Contributing factors to insulin resistance and type 2 diabetes include genetics, obesity, physical inactivity, unhealthy diet, aging, and certain medications.

In both types of diabetes, there is high blood glucose (hyperglycemia) due to insufficient insulin action or secretion. This can lead to the characteristic symptoms of diabetes, such as frequent urination, excessive thirst, and increased hunger. Over time, high blood glucose levels can also cause damage to various organs and tissues in the body, leading to complications such as cardiovascular disease, neuropathy, and kidney damage.

Clinical Feature

The clinical features of diabetes mellitus (both type 1 and type 2) include:

• Polyuria: Increased urination due to excess glucose in the blood.

• Polydipsia: Excessive thirst due to dehydration caused by increased urination.

• Polyphagia: Increased hunger and appetite, particularly after eating carbohydrates.

• Weight loss: Unintentional weight loss may occur due to the body breaking down fats and proteins to obtain energy when glucose is not available.

• Fatigue: Feeling tired or weak due to the body not being able to use glucose for energy.

• Blurred vision: High blood glucose levels can lead to swelling of the lens in the eye, causing blurry vision.

• Slow healing: Wounds and infections take longer to heal due to the body's reduced ability to fight infections.

• Numbness and tingling: Neuropathy (nerve damage) may occur, leading to numbness and tingling sensations in the hands and feet.

• Erectile dysfunction: Men with diabetes may experience erectile dysfunction due to damage to the blood vessels and nerves that control erections.


Diabetes mellitus can be diagnosed using various tests, including:

• Fasting plasma glucose (FPG) test: A blood test to measure the glucose levels after fasting for at least 8 hours. A level of 126 mg/dL or higher indicates diabetes.

• Oral glucose tolerance test (OGTT): A blood test to measure the glucose levels after fasting for at least 8 hours and then drinking a sugary solution. A level of 200 mg/dL or higher after 2 hours indicates diabetes.

• Hemoglobin A1c (HbA1c) test: A blood test that measures the average blood glucose levels over the past 2-3 months. A level of 6.5% or higher indicates diabetes.

• Random plasma glucose test: A blood test to measure the glucose levels at any time of the day. A level of 200 mg/dL or higher indicates diabetes if accompanied by other symptoms.

It is important to note that these tests should be confirmed with a repeat test on another day before a diagnosis of diabetes is made.


The treatment of diabetes mellitus depends on the type and severity of the condition, as well as the individual's overall health status. The following is a general overview of treatment options for both type 1 and type 2 diabetes:

Type 1 Diabetes:

Insulin therapy: 

Since the pancreas does not produce enough insulin, insulin injections are required to regulate blood sugar levels. Types of insulin include rapid-acting, short-acting, intermediate-acting, and long-acting insulin. Examples of popular brand names include Humalog, NovoLog, Regular, NPH, and Lantus.

Continuous glucose monitoring (CGM): 

This involves the use of a device that measures blood sugar levels continuously and alerts the individual when levels are too high or low. Examples of popular brand names include Dexcom and Freestyle Libre.

Type 2 Diabetes:

Lifestyle changes: 

This includes a healthy diet, regular exercise, and weight loss if necessary to help regulate blood sugar levels.

Oral medications: 

Various classes of oral medications are available that work to lower blood sugar levels in different ways. Examples include metformin, sulfonylureas, DPP-4 inhibitors, GLP-1 receptor agonists, and SGLT2 inhibitors. Popular brand names include Glucophage, Glyburide, Januvia, Victoza, and Farxiga.

Insulin therapy: 

In some cases, insulin injections may be necessary if oral medications alone are not effective in controlling blood sugar levels.


Diabetes mellitus can cause a wide range of complications that affect various parts of the body. Some of the most common complications include:

Cardiovascular complications: 

Diabetes increases the risk of heart attack, stroke, and other cardiovascular diseases. This is due to the damage high blood sugar levels can cause to the blood vessels and nerves that control the heart and blood vessels.

Kidney damage: 

High blood sugar levels can damage the small blood vessels in the kidneys, leading to kidney damage and ultimately kidney failure.

Nerve damage: 

Diabetes can cause nerve damage, or neuropathy, which can lead to numbness, tingling, and pain in the hands, feet, and legs. It can also affect the nerves that control the digestive system, causing problems with digestion and bowel movements.

Eye damage: 

High blood sugar levels can damage the blood vessels in the eyes, leading to diabetic retinopathy, a condition that can cause vision loss and blindness.

Foot problems: 

Diabetes can cause poor blood flow and nerve damage in the feet, leading to foot ulcers, infections, and in severe cases, amputation.

Skin conditions: 

People with diabetes are more prone to skin infections and conditions, such as bacterial and fungal infections, and itching.

Dental problems: 

Diabetes can increase the risk of gum disease, cavities, and tooth loss.

Sexual dysfunction: 

High blood sugar levels can cause damage to the blood vessels and nerves that control sexual function, leading to erectile dysfunction in men and decreased sexual arousal in women.

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