Type I

By Peter Galvin, MD

Type I diabetes occurs when the immune system destroys the insulin-producing cells (Islets of Langerhans) in the pancreas, leading to high blood sugar. Insulin, a hormone, enables glucose to cross from the bloodstream into cells where glucose is the fuel that cells need to function. Without insulin, glucose rapidly builds up to toxic levels in the blood. Type I diabetes only accounts for 5% to 10% of all cases of diabetes. Most cases of diabetes are type II, in which insulin is produced, but in insufficient quantity with insulin resistance a factor. Type I diabetes affects approximately 8.4 million people worldwide and approximately 2 million people in the U.S. Although type I can occur at any age, it is most commonly diagnosed in adolescence.

While people who have a first-degree relative with type I diabetes are more likely to develop the disease, 85% of those with type I do not have a family member with it. Type I diabetes is more commonly diagnosed in fall and winter, likely because viral infections, which are more common during these months, are thought to be the trigger that stimulates the immune system to destroy the insulin-producing cells. The mechanism of this trigger has yet to be discovered. Patients with type I diabetes often have increased thirst, frequent urination, and unexplained weight loss (the same symptoms seen in type II diabetes). Other symptoms can include increased hunger, fatigue, and blurred vision. Young children may develop irritability, lethargy, and new-onset bed wetting. At the time of diagnosis, up to 44% of children and 23% of adults have diabetic ketoacidosis, a serious and potentially fatal condition that causes abdominal pain, nausea, and vomiting and requires hospitalization and treatment with intravenous insulin and fluids.

Type I diabetes is diagnosed based on symptoms and a random blood sugar level of 200 or higher or a hemoglobin A1c level of 6.5% or higher. A type I diagnosis is confirmed by the presence of specific blood antibodies targeting the pancreas, which are found in 90% to 95% of patients at the time of diagnosis. Those with type I diabetes need lifelong insulin treatment as, once they are destroyed, there is currently no way to restore or replace the insulin-producing cells. Today in the U.S., most type I patients are treated with automated insulin pumps which can prevent low blood sugar (hypoglycemia) and maintain fasting target glucose levels of 80 to 130, and postprandial (after meals) levels at less than 180. Insulin pumps provide continuous insulin that is adjusted throughout the day based on blood glucose levels recorded by a continuous glucose monitor attached to the skin. These systems usually involve the use of a smartphone.

Alternative treatment may be multiple daily insulin injections using both long-acting insulin supplemented by rapid-acting insulin at mealtimes. Those with type I diabetes are usually referred to a dietician for an individualized eating plan and ongoing nutritional counseling, and their care is usually overseen by an endocrinologist. More than 95% of those with type I disease will develop at least one diabetes-related complication (eyes, kidneys, peripheral nerves, or heart) but maintaining glucose levels in the target range can lessen the risk of complications. Heart disease is usually the cause of death in those with type I diabetes, and their life expectancy is unfortunately about 8 to 10 years shorter than those without type I diabetes.

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