Type 1 diabetes mellitus is an autoimmune disease that involves destruction of the insulin-secreting cells of the pancreas, leading to impaired insulin secretion, high levels of glucose in the blood (hyperglycemia), and eventually insulin resistance.
Early symptoms are related to hyperglycemia and include excessive thirst, excessive hunger, excessive urination, and blurred vision.
Doctors diagnose type 1 diabetes by measuring blood sugar levels and by checking for evidence that the body's immune system is attacking the cells in the pancreas that produce insulin.
Diabetes can damage blood vessels and increase the risk of heart attack, stroke, chronic kidney disease, and vision loss.
Diabetes can damage nerves and cause problems with the sense of touch.
People with type 1 diabetes need to take insulin and follow a healthy diet that is low in refined carbohydrates (including sugar), saturated fat, and processed foods. They also need to exercise and maintain a healthy weight.
Type 1 diabetes mellitus is an autoimmune disorder in which the amount of sugar in the blood is elevated. In an autoimmune disorder, the body's normal defense mechanisms attack its own cells as if they were foreign.
(See also Diabetes Mellitus in Children and Adolescents.)
Causes of Type 1 Diabetes Mellitus
The hallmark of type 1 diabetes is:
Autoimmune destruction of cells of the pancreas, leading to inadequate insulin production
In type 1 diabetes mellitus, insulin production is absent or severely deficient because of autoimmune destruction of pancreatic cells. The autoimmune reaction may possibly be triggered by an environmental exposure in people who are genetically susceptible. Destruction progresses slowly over months or years until so many cells are destroyed that the pancreas can no longer produce enough insulin to control blood glucose levels. Type 1 diabetes generally develops in childhood or adolescence and is most common form diagnosed before age 20 years; however, it can also develop in adults.
The genes that make people susceptible to environmental exposures include those that regulate insulin production and processing. These genes are more common in people with ancestry from certain geographic regions such as Scandinavia and Sardinia.
Antibodies to cells and proteins involved in the production of insulin can be detected in the body and provide evidence that diabetes is type 1 diabetes.
Several viruses (especially coxsackievirus and SARS-CoV-2 [COVID-19], as well as congenital cytomegalovirus and rubella, and potentially retroviruses) have been linked to the onset of type 1 diabetes. Viruses may directly infect and destroy pancreas cells, or they may cause cell destruction indirectly.
Diet may also be a factor. Intake of cow's milk, oats, gluten, and dietary fiber during infancy is associated with an increased risk of type 1 diabetes. Sugar and carbohydrate intake, vitamin D supplementation, nitrite, and protein may also be associated with the development of type 1 diabetes, but it is unclear exactly how these factors are related. Some dietary factors, including later introduction of cow's milk, gluten, and fruit, may protect against the development of diabetes.
Autoimmune diabetes can develop in adulthood (called latent autoimmune diabetes of adulthood [LADA]) and is often more slowly progressive than childhood type 1 diabetes.
Some cases of type 1 diabetes do not appear to be autoimmune in nature and the cause is not known.
Screening and Prevention of Type 1 Diabetes Mellitus
Screening
Screening for type 1 diabetes is not recommended for most children or adults. Doctors sometimes do tests to screen for type 1 diabetes in people at high risk of type 1 diabetes (such as siblings or children of people who have type 1 diabetes). Testing for autoantibodies to insulin or to cells and proteins that make and release insulin allow doctors to identify people with early stage type 1 diabetes and start preventive measures.
Prevention
No treatments can completely prevent type 1 diabetes mellitus. However, family members of people with type 1 diabetes who have autoantibodies but have not yet had symptoms of diabetes (stage 1), may benefit from a medication (teplizumab). This medication can prolong the ability of the pancreas to produce No treatments can completely prevent type 1 diabetes mellitus. However, family members of people with type 1 diabetes who have autoantibodies but have not yet had symptoms of diabetes (stage 1), may benefit from a medication (teplizumab). This medication can prolong the ability of the pancreas to produceinsulin and delay the onset of symptoms of type 1 diabetes.
Symptoms of Type 1 Diabetes Mellitus
Many people with diabetes may have no symptoms, especially in the early phase of the disease.
The symptoms of high blood glucose levels include:
Increased thirst
Increased urination
Increased hunger
When the blood glucose level rises above 160 to 180 mg/dL (8.9 to 10.0 mmol/L), glucose spills into the urine. When the level of glucose in the urine rises even higher, the kidneys excrete additional water. Because the kidneys produce excessive urine, people with diabetes urinate large volumes frequently (polyuria) and can become dehydrated. The excessive urination creates abnormal thirst (polydipsia). Because excessive calories are lost in the urine, people may lose weight. To compensate, people often feel excessively hungry.
Other symptoms of diabetes include:
Blurred vision
Drowsiness
Nausea
Decreased energy or endurance
In people with type 1 diabetes, the symptoms often begin abruptly and dramatically. A serious condition called diabetic ketoacidosis, a complication in which the body produces excess acid, may quickly develop. In addition to the usual diabetes symptoms of excessive thirst and excessive urination, the initial symptoms of diabetic ketoacidosis also include nausea, vomiting, fatigue, and—particularly in children—abdominal pain. Breathing tends to become deep and rapid as the body attempts to correct the blood’s acidity (see Acidosis), and the breath smells fruity or like nail polish remover. Without treatment, diabetic ketoacidosis can progress to coma and death, sometimes very quickly.
Type 1 diabetes progresses in stages: the disease usually starts with the development of antibodies indicating that the immune system is attacking the body's insulin-producing cells, followed by the development of high blood sugar, and finally followed by the development of symptoms.
Diagnosis of Type 1 Diabetes Mellitus
Measuring the level of glucose in the blood, sometimes while fasting or after consuming a standard amount of sugar
Sometimes autoantibodies
The diagnosis of diabetes is made when people have abnormally high levels of glucose in the blood, using a fasting glucose, hemoglobin A1C, or oral glucose tolerance test, and sometimes a random glucose level. See Overview of Diabetes - Diagnosis, for a more detailed discussion.
Once diabetes is diagnosed, doctors often do further tests, for autoantibodies, to determine whether an autoimmune reaction is the cause, indicating that the diabetes is type 1 diabetes.
The combination of the blood glucose level, the presence of autoantibodies, and whether the person has symptoms are used to determine the stage of type 1 diabetes.
Age is not a reliable method for diagnosing the specific type of diabetes because children and adults can develop both type 1 and type 2 diabetes.
Treatment of Type 1 Diabetes Mellitus
Insulin injections and blood glucose monitoringInsulin injections and blood glucose monitoring
Education
Diet
Medications to prevent complications
Insulin, education, and dietary management are the cornerstones of treatment of type 1 diabetes.
Because complications are less likely to develop if people with diabetes strictly control their blood glucose levels, the goal of diabetes treatment is to keep blood glucose levels as close to the normal range as possible, while minimizing the risk of dangerous episodes of low blood sugar.
It is helpful for people with diabetes to carry or wear medical identification (such as a bracelet or tag) to alert health care professionals to the presence of diabetes. This information allows health care professionals to start life-saving treatment quickly, especially in the case of injury or change in mental status.
People with diabetes should stop smoking and consume only moderate amounts of alcohol (up to one drink per day for women and two for men).
Medication treatment of diabetes
Insulin
People with type 1 diabetes almost always require insulin therapy and will become very sick without it. Usually, insulin is injected under the skin. The goal is to try to replicate the pattern of insulin secretion of a person who does not have diabetes, by using a relatively constant, long-acting form of insulin (basal) along with shorter-acting forms at mealtimes to help with the increased blood sugar.
Alternatively, an insulin pump releases insulin continuously from a reservoir through a small cannula (hollow plastic tube) that stays in the skin. The rate of insulin administration can be adjusted depending on the time of day, whether the person is exercising, or other parameters. People can release additional doses of insulin as needed for meals or to correct high blood glucose levels. The pump more closely mimics the way the body normally produces insulin compared with injections.
An insulin pump used with a continuous glucose monitor, an external device that is attached to the body and continuously records blood glucose levels, is called a hybrid closed-loop insulin-delivery system. With these systems (sometimes called an artificial pancreas), an algorithm is used to calculate and automatically deliver baseline insulin doses through an insulin pump based on input from a continuous glucose monitor. However, this device does not eliminate the need for people to monitor their blood glucose levels and program the pump to give bolus insulin before meals.
See Medications for the Treatment of Diabetes - Insulin for more information.
Other medications
Certain blood pressure medications (angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers) are given to people with diabetes and high blood pressure or chronic kidney disease.
Statins are given to many adults with diabetes, depending on their age and risk factors for atherosclerosis and coronary artery disease.
Diabetes education
People with diabetes benefit greatly from learning about the disorder, understanding how diet and exercise affect their blood glucose levels, and knowing how to avoid complications. A nurse or other clinician trained in diabetes education can provide information about managing diet, exercising, monitoring blood glucose levels, and taking insulin. Diabetes education is considered an important part of treatment in diabetes and, in addition to being provided at the time of diagnosis, doctors review and reinforce information at every visit., and taking insulin. Diabetes education is considered an important part of treatment in diabetes and, in addition to being provided at the time of diagnosis, doctors review and reinforce information at every visit.
Diet for people with diabetes
Diet management is very important for people with either type of diabetes mellitus. Doctors recommend a healthy, balanced diet and efforts to maintain a healthy weight. People with diabetes can benefit from meeting with a dietitian or a diabetes educator to develop an optimal eating plan. Such a plan might include limits on simple sugars, processed foods, and saturated fat as well as increased dietary fiber.
People with type 1 diabetes use carbohydrate counting or the carbohydrate exchange system to match their insulin dose to the carbohydrate content of their meal. "Counting" the amount of carbohydrate in a meal is used to calculate the amount of insulin the person takes before eating. However, the carbohydrate-to-insulin ratio (the amount of insulin taken for each gram of carbohydrate in the meal) varies for each person, and people with diabetes need to work closely with a dietician who has experience in working with people with diabetes to master the technique. Some experts have advised use of the glycemic index (a measure of the impact of an ingested carbohydrate-containing food on the blood glucose level) to delineate between rapid and slowly metabolized carbohydrates.
People who are taking insulin should avoid long periods between meals to prevent hypoglycemia. Although protein and fat in the diet contribute to the number of calories a person eats, only the number of carbohydrates has a direct effect on blood glucose levels. The American Diabetes Association has many helpful tips on diet, including recipes. Even when people follow a proper diet, cholesterol-lowering medication is needed to decrease the risk of heart disease.
There are no specific recommendations on the percentages of calories that should come from carbohydrate, protein, or fat. Adjusting diet to individual circumstances can help people control fluctuations in their glucose level. Dietary management should be individualized based on the person's age, size, activity level, tastes, preferences, culture, and goals and should also take into account other medical conditions. People should consume a diet rich in whole foods rather than processed foods. Carbohydrates should be high quality and should contain adequate amounts of fiber, vitamins, and minerals and be low in added sugar, fat, and sodium.
Exercise for people with diabetes
Exercise, in appropriate amounts (at least 150 minutes a week spread out over at least 3 days, or whatever the patient can manage if other health conditions limit exercise), can also help people control their weight and improve blood glucose levels. Because blood glucose levels go down during exercise, people must be alert for symptoms of hypoglycemia. Some people need to eat a small snack during prolonged exercise, decrease their insulin dose, or both.
Foot care
Foot care is critical (see Foot Care). The feet should be protected from injury, and the skin should be kept moist with a good moisturizer. Shoes should fit properly and not cause areas of irritation. Shoes should have appropriate cushioning to spread out the pressure caused by standing. Going barefoot is ill advised. Regular care from a podiatrist (a doctor specializing in foot care), such as having toenails cut and calluses removed, may also be helpful. Also, sensation and blood flow to the feet should be regularly evaluated by doctors.
Vaccination for people with diabetes
All patients with diabetes, including type 1 diabetes, should be receive recommended vaccines, including those against Streptococcus pneumoniae, influenza, hepatitis B, varicella, respiratory syncytial virus, and COVID-19.
Pancreas and islet cell transplantation
People with type 1 diabetes sometimes receive transplantation of an entire pancreas or of only the insulin-producing cells from a donor pancreas. This procedure may allow people with type 1 diabetes mellitus to maintain normal glucose levels. However, because immunosuppressant medications must be given to prevent the body from rejecting the transplanted cells, pancreas transplantation is usually done only in people who have serious complications due to diabetes or who are receiving another transplanted organ (such as a kidney) and will require immunosuppressants anyway.
Monitoring Type 1 Diabetes Treatment
Monitoring blood glucose levels is an essential part of diabetes care. Routine blood glucose monitoring provides the information needed to make necessary adjustments in medications, diet, and exercise regimens. It is potentially harmful to wait until there are symptoms of low or high blood glucose levels to check blood glucose.
Diabetes treatment goals
Experts recommend that people keep their blood glucose levels:
Between 80 and 130 mg/dL (4.4 and 7.2 mmol/L) fasting (before meals)
Less than 180 mg/dL (10.0 mmol/L) 2 hours after meals
Hemoglobin A1C levels should be less than 7%.
Some people use a continuous glucose monitor (CGM), an external device that is attached to the body and continuously records blood glucose levels. When this type of device is used, doctors use a different measurement to determine how well blood glucose levels are being controlled. They use a value called time in range. Time in range is the percentage of time over a specific period that the blood glucose level is at the person's goal level. The usual range is 70 to 180 mg/mL (3.9 to 9.9 mmol/L).
Because aggressive treatment to reach these goals increases the risk that blood glucose might go too low (hypoglycemia), blood sugar goals are adjusted for some people in whom hypoglycemia is particularly undesirable, such as older adults.
Many things cause blood glucose levels to change:
Diet
Exercise
Stress
Illness
Medications
Time of day
The blood glucose levels may jump after people eat foods high in carbohydrates. Emotional stress, an infection, and many medications tend to increase blood glucose levels. Blood glucose levels increase in many people in the early morning hours because of the normal release of hormones (growth hormone and cortisol), a reaction called the dawn phenomenon. Blood glucose may shoot too high if the body releases certain hormones in response to low blood glucose levels (Somogyi effect). Exercise may cause the levels of glucose in the blood to fall low.
People with type 1 diabetes may have more frequent swings in blood glucose levels because insulin production is completely absent. Infection, delayed movement of food through the stomach, and other hormonal disorders may also contribute to large swings in blood glucose.
In people who have difficulty controlling blood glucose, doctors look for other disorders that might be causing the problem and also give people additional education on how to monitor diabetes and take their medications.
Monitoring blood glucose levels
Blood glucose levels can be measured easily at home or anywhere. People should keep a record of blood glucose levels and report them to their doctor or nurse, or bring their meter or CGM reader to visits, to help doctors and nurses provide advice in adjusting the dose of insulin. Many people can learn to adjust the insulin dose on their own as necessary.
A fingerstick glucose test is most often used to monitor blood glucose. Most blood glucose monitoring devices (glucose meters) use a drop of blood obtained by pricking the tip of the finger with a small lancet. The lancet holds a tiny needle that can be poked into the finger or placed in a spring-loaded device that easily and quickly pierces the skin. Most people find that the pricking causes only minimal discomfort. Then, a drop of blood is placed on a reagent strip. The strip contains chemicals that undergo changes depending on the glucose level. The glucose meter reads the changes in the test strip and reports the result on a digital display. Some devices allow the blood sample to be obtained from other sites, such as the palm, forearm, upper arm, thigh, or calf. Home glucose meters are smaller than a deck of cards.
Continuous glucose monitoring (CGM) systems use a small glucose sensor placed under the skin. The sensor measures blood glucose levels every few minutes. There are two types of CGMs, with different purposes:
Professional
Personal
Professional (or "blinded") CGMs collect continuous blood glucose information over a period of time (72 hours to up to 14 days). Clinicians use this information to make treatment recommendations. Professional CGMs do not provide data to the person with diabetes. The advantage of this type of CGM is that the person's behavior and treatment is not affected by the blood glucose results, so the CGM offers a more realistic snapshot of their blood glucose under real-life conditions.
Personal CGMs are used by the person and provide real-time blood glucose data on a small portable monitor or on a connected smart phone. Alarms on the CGM system can be set to sound when blood glucose levels drop too low or climb too high, so the device can help people quickly identify worrisome changes in blood glucose.
CGMs can be worn for up to 14 days, often do not require calibration, and can be used for insulin dosing without fingerstick glucose confirmation. There are also systems in which the CGM device communicates with insulin pumps to either stop delivery of insulin when blood glucose is dropping (threshold suspend), or to give daily insulin (hybrid closed loop system).
CGM systems are particularly helpful in certain circumstances, such as in people with type 1 diabetes who have frequent, rapid changes in blood glucose (particularly when the glucose levels sometimes go very low), which are difficult to identify with fingerstick testing. CGM systems allow people to measure the period of time that their blood glucose stays within a certain range, and doctors use this measurement to set goals for treatment and adjust insulin dose. Even in people who don't use insulin, CGM systems can provide valuable information about how different foods and activities affect their blood sugar. dose. Even in people who don't use insulin, CGM systems can provide valuable information about how different foods and activities affect their blood sugar.
Hemoglobin A1C
Doctors can monitor treatment using a blood test called hemoglobin A1C. When the blood glucose levels are high, changes occur in hemoglobin, the protein that carries oxygen in the blood. These changes are in direct proportion to the blood glucose levels over an extended period. The higher the hemoglobin A1C level, the higher the person's glucose levels have been. Thus, unlike the blood glucose measurement, which reveals the level at a particular moment, the hemoglobin A1C measurement demonstrates whether the blood glucose levels have been controlled over the previous few months.
People with diabetes aim for a hemoglobin A1C level of less than 7%. Achieving this level is sometimes difficult, but the lower the hemoglobin A1C level, the less likely people are to have complications. Doctors may recommend a slightly higher or lower target for certain people depending on their particular health situation. However, levels above 9% show poor control, and levels above 12% show very poor control. Most doctors who specialize in diabetes care recommend that hemoglobin A1C be measured every 3 to 6 months.
Fructosamine
Fructosamine, an amino acid that has bonded with glucose, is also useful for measuring blood glucose control over a period of a few weeks and is generally used when hemoglobin A1C results are not reliable, such as in people who have anemia caused by deficiency of iron, folate, or vitamin B12, or abnormal forms of hemoglobin such as those in sickle cell disease or thalassemia.
Urine testing
Ketones are chemicals produced by your body when it uses fat for fuel. This happens when there is not enough insulin to move glucose (sugar) into the cells where it can be used for fuel. People with type 1 diabetes should measure ketones in the urine if they experience symptoms, signs, or triggers of ketoacidosis, such as nausea or vomiting, abdominal pain, fever, cold or flu-like symptoms, especially if they have hypoglycemia or sustained hyperglycemia.
Although urine can also be tested for the presence of glucose, checking urine is not a good way to monitor or adjust treatment. Urine testing can be misleading because the amount of glucose in the urine may not reflect the current level of glucose in the blood. Blood glucose levels can get very low or reasonably high without any change in the glucose levels in the urine.
Complications of Type 1 Diabetes Mellitus
Preventing, identifying, and treating the complications of diabetes is one of the main goals of diabetes care.
The acute (immediate) complications of type 1 diabetes and its treatment include diabetic ketoacidosis and hypoglycemia.
For a detailed discussion of specific complications, see Long-Term Complications of Diabetes Mellitus.
Long-term complications of type 1 diabetes
Most complications of all types of diabetes, including type 1 diabetes, are the result of problems with blood vessels. Glucose levels that remain high over a long time cause both microscopic and larger blood vessels to narrow for 2 reasons:
Complex sugar-based substances build up in the walls of microscopic blood vessels, causing them to thicken and leak.
Poor control of blood glucose levels causes the levels of fatty substances in the blood to rise, resulting in atherosclerosis and decreased blood flow in the larger blood vessels.
The thickening and narrowing reduces blood flow to many parts of the body, leading to problems, including eye problems, kidney disease, nerve problems, foot ulcers, atherosclerosis, stroke, and peripheral artery disease.
People with type 1 diabetes are also at risk for other autoimmune diseases. The most common of these are thyroid disease, celiac disease, and pernicious anemia (vitamin B12 deficiency). Less common associated diseases include Addison disease, autoimmune liver disease, and myasthenia gravis.
Screening for complications of type 1 diabetes
There are many screening tests given to people with type 1 diabetes. Shortly after diagnosis, people should have blood pressure, lipid levels, and thyroid function checked. About 5 years after diagnosis, people should start undergoing eye examinations, foot examinations, and kidney function screening by urine and blood tests. Most of these tests are done every 1 to 2 years for the rest of the person's life. Other screening tests, for heart failure, peripheral artery disease, pernicious anemia, and celiac disease, may be done based on a person's age, symptoms, or other risk factors.
More Information
The following English-language resources may be useful. Please note that The Manual is not responsible for the content of the resources.
American Diabetes Association: Comprehensive information on diabetes, including resources for living with diabetes
Breakthrough TD1 (previously called JDRF, or Juvenile Diabetes Research Foundation): General information on type 1 diabetes mellitus
National Institute of Diabetes and Digestive and Kidney Diseases: General information on diabetes, including on the latest research and community outreach programs
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