Type 1 vs. Type 2 Diabetes: Similarities and Differences

There are four major types of diabetes.

Diabetes mellitus is a group of metabolic diseases, all of which have in common high blood sugar (glucose) levels that result from problems with insulin secretion, its action, or both. Normally, blood glucose levels are tightly controlled by a hormone produced by the pancreas known as insulin. When blood glucose levels rise (for example, after eating food), insulin is released from the pancreas to normalize the glucose level.

The two main types of diabetes are type 1 and type 2 diabetes. While both result in elevated blood glucose levels, the causes and progression of type 1 vs. type 2 diabetes differ significantly.

An absolute lack of insulin, usually due to the destruction of the insulin-producing beta cells of the pancreas, is the main problem in type 1 diabetes.

Type 1 diabetes was formerly referred to as juvenile diabetes or insulin-dependent diabetes mellitus (IDDM). Its causes are different from type 2 diabetes.

Type 2 diabetes was previously called non-insulin-dependent diabetes mellitus (NIDDM), or adult-onset diabetes mellitus (AODM). People who have type 2 diabetes can still produce insulin but do so relatively inadequately for their body's needs.

Type 2 diabetes typically occurs in individuals over 30 years of age, and its incidence increases with advancing age. In contrast, type 1 diabetes is most often diagnosed in young people.

Genetics plays a role in the development of type 2 diabetes, and having a family history and close relatives with the condition increases your risk; however, there are other risk factors, with obesity being the most significant. There is a direct relationship between the degree of obesity and the risk of developing type 2 diabetes for both children and adults. It has been estimated that the risk of developing type 2 diabetes doubles for every 20% increase over desirable body weight.

The underlying causes of type 1 and type 2 are different.

Type 1 diabetes causes

Type 1 diabetes is believed to be due to an autoimmune process, in which the body's immune system mistakenly targets its tissues (islet cells in the pancreas). In people with type 1 diabetes, the beta cells of the pancreas responsible for insulin production are attacked by the misdirected immune system. This tendency for the immune system to destroy the beta cells of the pancreas is likely to be, at least in part, genetically inherited, although the exact reasons that this process happens are not fully understood.

Exposure to certain viral infections (mumps and Coxsackie viruses) or other environmental toxins have been suggested as possible reasons why abnormal antibody responses develop that cause damage to the pancreas cells.

Type 2 diabetes causes

The primary problem in type 2 diabetes is the inability of the body's cells to use insulin properly and efficiently, leading to high blood sugar (hyperglycemia) and diabetes. This problem affects mostly the cells of muscle and fat tissues and results in a condition known as insulin resistance. In type 2 diabetes, there also is a steady decline of beta cells that worsens the process of elevated blood sugars. In the beginning, if someone is resistant to insulin, the body can at least partially increase the production of insulin enough to overcome the level of resistance. Over time, if production decreases and enough insulin cannot be released, blood sugar levels rise. In many cases, this means the pancreas produces larger than normal quantities of insulin, but the body is not able to use it effectively. A major feature of type 2 diabetes is a lack of sensitivity to insulin by the cells of the body (particularly fat and muscle cells).

Difference between type 1 and type 2 diabetes

The causes of type 1 vs. type 2 diabetes differ, even though both involve elevated blood sugar. Type 1 diabetes is caused by an autoimmune attack on the insulin-producing cells in the pancreas, while type 2 diabetes is primarily due to insulin resistance and a gradual decline in insulin production. Type 1 typically develops in childhood or early adulthood and requires lifelong insulin therapy, whereas type 2 is more common in adults and is often linked to lifestyle factors such as obesity, inactivity, and poor diet.

Both diabetes type 1 and diabetes type 2 require good control over the diet by eating foods that help regulate blood sugar, exercise, and in most patients, medical treatments to allow the patient to remain in good health.

There isn't a difference between the symptoms of either disease. The "classic" symptoms are the same for both diabetes type 1 and type 2, which include:

• Increased urine output (polyuria)
• Increased thirst (polydipsia)
• Increased hunger (polyphagia )
• Unexplained weight loss

For both type 1 and type 2, early symptoms of untreated diabetes arise due to elevated blood sugar levels and the presence of glucose in the urine. High amounts of glucose in the urine can cause increased urine output and dehydration. Dehydration, in turn, causes increased thirst.

A lack of insulin or an inability of insulin to work properly affects protein, fat, and carbohydrate metabolism. Insulin normally encourages the storage of fat and protein, so when there is inadequate insulin or poorly functioning insulin, this eventually leads to weight loss despite an increase in appetite.

When comparing type 1 vs. type 2 diabetes, weight loss is more common and often more pronounced in type 1 due to the complete lack of insulin production. In type 2 diabetes, weight loss can occur but is typically less severe and more gradual.

Some untreated diabetes patients also experience generalized symptoms like fatigue, nausea, and vomiting. People with diabetes are also at risk for infections of the bladder, skin, and vaginal areas. Changes in blood glucose levels can lead to blurred vision. When blood sugar levels are extremely high, lethargy and coma can result.

Although the symptoms of type 1 and type 2 diabetes can be similar, the onset and progression of each type differ. In type 1 diabetes, symptoms tend to appear more suddenly, often in childhood or adolescence, whereas type 2 diabetes symptoms may develop more gradually, sometimes going unnoticed for years.

Signs and symptoms of diabetes, whether type 1 or type 2, do not differ in terms of the classic manifestations, such as increased thirst, frequent urination, and weight loss. However, there are some key differences in how and when these symptoms develop.

• Early diabetes may not produce any symptoms at all. This is especially true in type 2 diabetes, where symptoms can develop gradually and may go unnoticed for years. In contrast, type 1 diabetes symptoms often develop rapidly and may be more severe, leading to a quicker diagnosis.
• When symptoms do occur, the age of onset is typically different, with type 1 diabetes being diagnosed most often in younger people (in a child, for example), while type 2 diabetes is diagnosed more commonly in adults. However, this is not always the case.
• The increasing incidence of obesity among children and adolescents has caused a rise in the development of type 2 diabetes in young people. Previously, type 2 diabetes was primarily seen in adults.
• Further, some adults with diabetes may be diagnosed with a form of late-onset type 1 diabetes. While type 1 diabetes is typically diagnosed in childhood or adolescence, some individuals may develop the condition later in life, presenting with similar symptoms but often being initially misdiagnosed as having type 2 diabetes due to age.

It has been estimated that approximately 11.6% of the US population had diabetes in 2023. This corresponds to about 38.4 million people. This includes both diagnosed and undiagnosed cases.

Type 1 diabetes is much less common and affects about 1.259 million people. It is further estimated that of the 38.4 million people affected with diabetes, about 8.7 million people are undiagnosed, meaning that they have diabetes but are not aware of it. There has been an increase in the number of Americans with prediabetes. In 2010, 79 million people were estimated to have prediabetes. In 2012, this number was 86 million. By 2023, this number had risen to 97.6 million.

A fasting blood sugar measurement can be used to diagnose any type of diabetes. This test measures the level of sugar (glucose) in the bloodstream in the morning before eating breakfast. Normal fasting plasma glucose levels are less than 100 milligrams per deciliter (mg/dl). Fasting plasma glucose levels of more than 126 mg/dl on two or more tests on different days indicate diabetes. A random (non-fasting) blood glucose test can also be used to diagnose diabetes. A blood glucose level of 200 mg/dl or higher indicates diabetes.

Another test often used to diagnose diabetes is a blood test to measure levels of glycated hemoglobin (hemoglobin A1c), which provides a measure of the average levels of blood glucose over the past 3 months. Other names for the A1c test are the HbA1c and glycosylated hemoglobin tests. The A1c test can be used to diagnose both type 1 and type 2 diabetes, with a level of 6.5% or higher indicating diabetes.

Diagnostic tests for type 1 vs. type 2 diabetes: The tests to identify the abnormal antibodies produced by the immune system are used to diagnose type 1 diabetes. Some of the antibodies seen in type 1 diabetes include anti-islet cell antibodies, anti-insulin antibodies, and anti-glutamic decarboxylase antibodies. These tests are not typically needed for diagnosing type 2 diabetes, where insulin resistance is the primary cause.

The treatment approaches for type 1 vs. type 2 diabetes differ significantly, as the underlying causes and mechanisms of the two conditions are distinct. Here’s an overview:

• Type 1 treatment: Insulin is the treatment of choice for type 1 diabetes because the body responds appropriately to insulin and the problem is a lack of insulin production by the pancreas.
• Type 2 treatment: Treatment for type 2 is more complicated because the body may produce enough insulin but not be able to use this insulin effectively. For many people with prediabetes or early-stage type 2, lifestyle modifications may be sufficient to control the problem. These can include regular physical activity, weight loss, and following a healthy diet plan to avoid becoming obese.

When lifestyle changes are not enough to control blood sugar levels in people with type 2, medications may be added. There are a great many types, or classes, of drugs that are used to treat this form of the disease, and there are too many to list. These drugs often are used in combination.

The classes of drugs include:

• Sulfonylureas, for example, glyburide (DiaBeta) and glipizide (Glucotrol), stimulate the beta cells of the pancreas to produce more insulin.
• Biguanides, for example, metformin (Glucophage), decrease glucose production by the liver.
• Meglitinides, for example, repaglinide (Prandin) and Nateglinide (Starlix), are a drug class that stimulates insulin production. 
• Thiazolidinediones, for example, pioglitazone (Actos) and rosiglitazone (Avandia), lead to more effective insulin action in fat and muscle tissues and also decrease glucose production in the liver
• DPP-IV inhibitors, for example, sitagliptin (Januvia) and linagliptin (Tradjenta), are a newer class of drugs that work by preventing the breakdown of a naturally occurring compound in the body, GLP-1, that reduces blood glucose levels in the body.
• SGLT2 inhibitors, for example, canagliflozin (Invokana) and dapagliflozin (Farxiga), cause excess glucose to be excreted in the urine.
• Alpha-glucosidase inhibitors, for example, acarbose (Precose), act by blocking or slowing the breakdown of starches and sugars after eating.
• Bile acid sequestrants lower blood cholesterol and typically reduce blood sugar in the process.
• GLP-1 agonists (also known as GLP-1 receptor agonists, incretin mimetics, or GLP-1 analogs) for example, Ozempic (semaglutide), exenatide (Byetta, Bydureon), liraglutide (Victoza), dulaglutide (Trulicity), and lixisenatide (Adlyxin). cause the body to make more insulin when blood sugar rises by mimicking how the hormone glucagon-like peptide 1 works in the body.

This depends upon the individual, including any other health conditions that are present and whether complications of diabetes have developed. Because of the development of complications, studies have shown that on average, those with type 1 diabetes have a life expectancy that is still 12 years below the average.

A recent study indicates the type 1 diabetes life expectancy gap has narrowed somewhat, but it remains significantly lower than that of the general population.

Other studies have shown that type 2 diabetes also reduces average life expectancy by about 5 to 10 years on average, with variations depending on how well the condition is managed and whether complications such as heart disease or kidney damage have developed. Type 2 diabetes life expectancy reduction can be closer to the lower end of this range for people with well-controlled type 2 diabetes. It's important to remember that these are only averages based on people who have had diabetes in the past and may be affected by including people who do not receive medical care or who have poor control over their diabetes. Advances in modern treatments, including improvements in insulin therapy, continuous glucose monitoring, and the development of new medications, are likely to reduce these gaps. Additionally, taking steps to make sure your diabetes is well-controlled, managing other risk factors like hypertension or high cholesterol, and leading a healthy lifestyle can further reduce the risk of death from complications.

Acute (sudden) complications of both types can be related to:

• Severely elevated blood sugar levels due to an actual lack of insulin or insufficient action of insulin. This leads to conditions called diabetic ketoacidosis or hyperosmolar coma, which can be life-threatening. However, diabetic ketoacidosis is more commonly seen in type 1 vs. type 2 diabetes due to the complete lack of insulin. However, it can also occur in type 2 diabetes, particularly during severe illness or when insulin resistance is pronounced.
• Abnormally low blood sugar levels (hypoglycemia) due to too much insulin or other glucose-lowering medications. However, it is more frequent in type 1 diabetes because insulin therapy is more intensive. In type 2, hypoglycemia is more often related to medications like sulfonylureas or insulin when used.

Long-term complications of either type are related to damage to blood vessels. These complications generally are referred to as small vessel disease, involving the eyes, kidneys, and nerves, and large vessel disease, involving the heart and blood vessels. For example, diabetic neuropathy refers to damage to the nerves that can cause numbness and tingling, among other symptoms.

Any type of diabetes accelerates blood vessel damage due to hardening of the arteries (atherosclerosis), leading to coronary heart disease (angina or heart attack), strokes, and pain in the lower extremities because of lack of blood supply (claudication).

When comparing type 1 vs. type 2 diabetes, it is not always clear-cut to say one is definitively "worse" than the other, as both carry significant risks but differ in their onset, progression, and complications.

Type 1 diabetes is often considered more immediately dangerous because it typically develops in childhood or adolescence and requires strict insulin management to prevent life-threatening conditions like diabetic ketoacidosis (DKA), which result from a lack of insulin. Without proper insulin therapy, type 1 diabetes can be fatal.

In contrast, type 2 diabetes develops more gradually and is usually diagnosed in adulthood, often linked to factors such as obesity, physical inactivity, and genetics. While type 2 diabetes is less immediately life-threatening, it poses serious long-term risks if not managed properly, including cardiovascular disease, kidney damage, and nerve damage (neuropathy). Over time, poorly controlled type 2 diabetes can lead to severe complications affecting multiple organs.

Therefore, type 1 diabetes is often more urgent due to its acute risks, while type 2 diabetes tends to be more harmful in the long term due to its potential for chronic, progressive health issues. Both conditions require careful, ongoing management to prevent serious complications.

There is no known way to prevent type 1 diabetes, and for some people, it might not be possible to prevent the development of type 2. For others, maintaining a healthy weight, getting regular exercise, and a healthy, balanced diet may help prevent or delay the onset of type 2 diabetes and thus preserve health.

• Which is deadlier type 1 or type 2 diabetes? Type 1 diabetes is generally considered more dangerous in the short term than type 2 diabetes. That’s particularly because type 1 diabetes often develops in childhood or early adulthood and requires constant insulin management to prevent life-threatening complications such as diabetic ketoacidosis. Type 2 diabetes, though serious, is often more manageable with lifestyle changes and medication, and its complications tend to develop more slowly over time. However, both types can lead to severe long-term complications, including heart disease, kidney failure, and neuropathy, especially if left untreated.
• Which is more harmful, type 1 or type 2 diabetes? Type 1 diabetes is often considered more immediately harmful due to its rapid onset and the need for lifelong insulin therapy, with a higher risk of acute complications such as diabetic ketoacidosis. Type 2 diabetes, while less urgent initially, can be more harmful in the long term, as it can lead to chronic complications such as heart disease, kidney failure, and neuropathy if not managed properly. Both types of diabetes require ongoing management to prevent severe health outcomes.
• Which is more serious, diabetes type 1 or diabetes type 2? Type 1 vs. type 2 diabetes differ in how they impact health in the short and long term. Type 1 diabetes is generally considered more serious in the short term because it often develops rapidly and requires immediate and lifelong insulin therapy to prevent life-threatening complications such as diabetic ketoacidosis. Type 2 diabetes, while it progresses more gradually, can also be very serious over time, leading to chronic complications such as heart disease, stroke, and kidney failure if not well-managed. Both types of diabetes require vigilant management to minimize the risk of severe health problems.
• Does diabetes 2 turn into diabetes 1? Type 2 diabetes does not turn into type 1 diabetes. They are distinct conditions: type 1 diabetes is an autoimmune condition in which the immune system attacks and destroys insulin-producing cells in the pancreas, while type 2 is typically caused by insulin resistance and lifestyle factors. Though both conditions involve high blood sugar, they have different underlying causes, progression, and treatment and cannot transform into one another.