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Type 1 Diabetes: Symptoms, Causes, and Treatments

  • A chronic disorder in which the body doesn’t produce insulin, leading to high blood glucose levels
  • Symptoms include increased urination and thirst, fatigue, blurred vision
  • Treatment includes lifestyle changes, medication, blood glucose monitoring, patient education, pancreas transplantation
  • Involves endocrinology, internal medicine, Diabetes Center, pediatric endocrinology & diabetes, pediatric diabetes program
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Type 1 Diabetes: Symptoms, Causes, and Treatments


Over 37 million people in the United States have diabetes. About 5% of these cases—or around 1.9 million people—are type 1 diabetes, a chronic disease in which the body makes little to no insulin. This results in high levels of glucose (a type of sugar) in the blood. High glucose levels can damage blood vessels and cause serious problems with the eyes, kidneys, heart, and nerves.

Type 1 diabetes most frequently occurs in children, teens, and young adults, but it can arise in people of any age and of any size. It can cause a range of symptoms, including more frequent urination than usual, increased thirst, weight loss, fatigue, and blurry vision. It’s important to note that unlike with type 2 diabetes, there is no way to prevent type 1 diabetes from occurring.

Fortunately, type 1 diabetes can be managed with lifestyle changes, blood glucose monitoring, and medications, such as insulin, that help lower blood glucose levels.

“Having type 1 diabetes means that you will need to use insulin,” says Yale Medicine endocrinologist Anika Anam, MD. “In the past few decades, there have been tremendous advancements in the management of type 1 diabetes. For example, there are several different types of insulin, new ways to deliver insulin to your body—via insulin pumps that use algorithms to adjust the rates of insulin being delivered, and easier ways to measure glucose, such as with continuous glucose monitors. It can take time to get used to using insulin if this is new for you, but with the guidance of your physician and diabetes team, you will be able to get a treatment plan tailored to your unique needs.”

What is type 1 diabetes?

Type 1 diabetes, also known as type 1 diabetes mellitus, is a chronic disorder characterized by high levels of glucose in the blood.

Glucose is the main source of energy for the body’s cells. When a person eats food—a plate of pasta or an apple, for instance—the food passes into the stomach, where it is broken down into individual nutrients, including glucose. The glucose then enters the bloodstream, which transports it throughout the body.

Cells around the body use the glucose as an energy source. To help the glucose enter each of these cells, the body uses insulin, a hormone produced by the pancreas. In a healthy body, the pancreas produces enough insulin to move glucose from the blood into cells, and blood glucose levels stay within a normal range.

In people with type 1 diabetes, however, the pancreas makes little to no insulin. As a result, glucose accumulates in the blood, resulting in high blood glucose levels (known as hyperglycemia). High blood glucose levels cause many symptoms, such as blurry vision and increased urination, and over time, can lead to serious complications.

People with type 1 diabetes need to take insulin every day so that glucose can move into cells, which prevents blood glucose levels from getting too high.

What causes type 1 diabetes?

For those with type 1 diabetes, it’s not yet known why the pancreas stops making insulin. Researchers believe it may be caused by the destruction of beta cells (the insulin-producing cells in the pancreas) by the body’s own immune system. This process may go on for months or years before enough beta cells are destroyed to cause symptoms. Researchers also believe the condition likely occurs due to genetic factors, such as a family history of type 1 diabetes. That said, type 1 diabetes may develop even in people without a family history. Researchers are also investigating the role of environmental factors, such as exposure to certain viruses.

What are the symptoms of type 1 diabetes?

Symptoms of type 1 diabetes may include:

  • Increased urination
  • Waking at night to urinate
  • Loss of control over urination, especially while sleeping (bedwetting)
  • Increased thirst, appetite, and hunger
  • Feeling tired
  • Weakness
  • Blurred vision
  • Unintentional weight loss
  • Slow-healing wounds

What are the complications of type 1 diabetes?

People with type 1 diabetes are at increased risk for certain complications, including:

People with type 1 diabetes who have high blood glucose levels can also develop a complication called diabetic ketoacidosis (DKA). In DKA, because the body’s cells are unable to get energy from glucose, they instead break down fats for energy. This process produces compounds called ketones, which build up in the blood, making it more acidic. DKA is a life-threatening complication marked by deep and rapid breathing, fruity smelling breath, headache, nausea and stomach pain, confusion, and loss of consciousness.

How is type 1 diabetes diagnosed?

Diagnosis of type 1 diabetes usually involves a review of the patient’s medical history, a physical exam, and one or more blood tests.

Doctors often begin to make a diagnosis by asking whether the patient has any symptoms or risk factors for types 1 diabetes, such as a family history of the disease. The doctor will also conduct a thorough physical exam to check for signs of the disease.

One or more of the following blood tests, which measure blood glucose levels, are necessary to confirm diagnosis:

  • Fasting plasma glucose (FPG) test. This test measures blood glucose levels after the patient has been fasting for 8 or more hours. Diabetes is diagnosed if the FPG level is 126 mg/dL (milligrams per deciliter) or higher.
  • Hemoglobin A1C (HbA1C) test. Also called A1C, this test measures a patient’s average blood glucose level over the previous 3 months. An A1C level of 6.5% or higher indicates diabetes.
  • Random plasma glucose (RPG) test. This test measures blood glucose levels. Patients don’t need to fast for this test. Diabetes is diagnosed in people who have symptoms and RPG levels of 200 mg/dL or higher.
  • Oral glucose tolerance test (OGTT), which assesses how well the patient’s body processes glucose. For this test, the patient has their blood drawn after fasting for at least 8 hours to establish their fasting blood glucose level. The patient then drinks a beverage that contains a concentrated dose of glucose. Blood is drawn and tested for glucose levels at intervals of 1, 2, and sometimes 3 hours. Diabetes is diagnosed if the 2-hour blood glucose level is 200 mg/dL or above.

If a blood test indicates that the patient has diabetes, the doctor will also need to determine whether the patient has type 1 or type 2 diabetes. To do so, he or she takes into account the patient’s symptoms and age, and may order additional blood tests to check for the presence of certain antibodies or other compounds.

How is type 1 diabetes treated?

Type 1 diabetes treatment aims to control blood glucose levels with the goal of keeping them as close to normal levels as possible. Regulating glucose levels helps to relieve diabetes symptoms and reduce the risk of developing complications.

Treatments may include:

  • Patient education. People with type 1 diabetes should learn about their diabetes and how to manage it on their own. Dietitians, nurses, and other specialists help the patient understand the relationship between diet, exercise, and blood glucose levels, when to take insulin, and when to test blood glucose levels, along with other aspects of managing the disorder.
  • Insulin. All people with type 1 diabetes must take insulin daily to keep blood glucose levels from getting too high. There are several types of insulin. Rapid-acting insulin acts very quickly to reduce blood glucose levels—in around 15 minutes—and is usually taken before meals. Short-acting or regular insulin usually takes about 30 minutes to begin lowering glucose levels, while intermediate-acting insulin takes effect after 2 to 4 hours. Long-acting insulin is also taken daily. Insulin is usually injected under the skin using either a syringe and needle, an insulin pen, or an insulin pump. A rapid-acting inhaled insulin is also available.
  • Teplizumab. In November 2022, the Food and Drug Administration (FDA) approved teplizumab for children and adults 8 years of age and older who have stage 2 type 1 diabetes. The drug, a monoclonal antibody, delays the onset of clinical type 1 diabetes, also known as stage 3 type 1 diabetes. A Phase 2 clinical trial, the results of which were published in 2021, found that daily infusions of teplizumab for 14 days delayed the onset of clinical type 1 diabetes in people ages 8 and over with stage 2 type 1 diabetes. More recently, Phase 3 trial, published in October 2023, showed that two 12-day courses of teplizumab helps preserve the function of beta cells (the cells in the pancreas that make insulin and are destroyed in people with type 1 diabetes), meaning it helps people continue to make insulin. The phase 3 trial involved children and teens aged 8 to 17 who had been diagnosed with clinical (stage 3) type 1 diabetes within six weeks of the trial.
  • Lifestyle changes. Eating a healthy diet and getting exercise are key components of treatment of type 1 diabetes. Exercise and diet can help people maintain a healthy body weight, reduce the risk of cardiovascular complications, and achieve better control of their blood glucose levels. Health care providers can educate patients on insulin dosing and timing around meals and exercise.
  • Blood glucose monitoring. Testing and keeping track of blood glucose levels lets patients know how different foods and activities affect their glucose levels and whether their blood glucose levels are too high. This usually involves a fingerstick and use of a device called a glucose meter to measure blood glucose levels. A continuous glucose monitoring (CGM) device, which measures glucose levels throughout the day, may be inserted under the skin and worn by the patient. The CGM can communicate the glucose levels to the patient’s smartphone or insulin pump, too, which makes managing diabetes easier.
  • Other medications. Because type 1 diabetes increases risk for cardiovascular disease, people with this disease may take statins to lower cholesterol levels, and those who have high blood pressure may use medications to control blood pressure and protect their kidneys.
  • Pancreas transplantation. Some patients may be candidates for a pancreas transplantation or transplantation of the cells in the pancreas that produce insulin.

Can type 1 diabetes be prevented?

There is no known way to prevent type 1 diabetes. Researchers are actively investigating methods for preventing it.

What is the outlook for people with type 1 diabetes?

Type 1 diabetes is a chronic condition that requires lifelong treatment and monitoring. Unfortunately, there is no cure, but with good control of blood glucose levels and lifestyle changes, people with type 1 diabetes can delay or even prevent the onset of many complications associated with the disorder.

It’s important for people with type 1 diabetes to see their doctor every few months for a checkup and blood work. This allows doctors to adjust treatment as needed and to monitor for and manage any complications as soon as they start to develop.

What stands out about Yale Medicine's approach to type 1 diabetes?

“The Yale Diabetes Center specializes in type 1 and type 2 diabetes, as well as prediabetes and metabolic syndrome,” says Dr. Anam. “The Yale Diabetes Center includes a team of physicians and nurse practitioners experienced in diabetes management to provide comprehensive care focusing on lifestyle management, medications, and using new diabetes technologies. Importantly, Yale and Yale Diabetes Center are committed to improving our understanding and treatment of diabetes, and Yale is at the leading edge for diabetes research. There are several research studies and clinical trials occurring at Yale, for example in screening, prevention, and newer diabetes therapies.”

Visit the Yale Medicine Diabetes Content Center for more diabetes-related articles and videos.