The effects of type 1 diabetes on the production of insulin and glucose, and how they interact with the blood and tissues. Illustration by Nguyet M Le.

Type 1 in Focus

Type 1 diabetes is a highly complex disease. Much is known about it, but much remains unclear—including the path to a real cure. Those with the disease, or their loved ones, can gain access to a wealth of information and education about causes, effects, treatment, and efforts toward a cure. Giving such a comprehensive picture isn’t our purpose here, but we can offer a few basics, along with observations and opinions that may be helpful.

The Basic Facts

Type 1 diabetes used to be called juvenile-onset or insulin-dependent diabetes. Records of the disease date back to around 1500 BC, and until the discovery of insulin in the 1920s, its progression was inevitably fatal. See A Short Biography of Type 1.

Type 1 can occur at any age, but it is most often diagnosed in children, adolescents, or young adults. In adults, type 1 accounts for approximately 5 percent of all diagnosed cases of diabetes. A variant of T1D, called LADA (Latent Autoimmune Diabetes of Adults) affects adults from 20 to 70 years of age. Because it develops much more slowly than T1D, it is sometimes misdiagnosed as type 2.

Risk factors for type 1 may be autoimmune, genetic, or environmental. There is no proven way to prevent type 1 diabetes, but several clinical trials aimed at prevention are currently in progress or are being planned.

The exact cause is unknown, but most likely there is a viral or environmental trigger in genetically susceptible people that causes an autoimmune reaction. The body’s white blood cells mistakenly attack the insulin-producing beta cells in the islets of Langerhans of the pancreas, leading to progressive and irreversible destruction of those cells. Within 5 to 10 years, in most cases, the beta cells are completely nonfunctional and the body can no longer produce insulin.

Without enough insulin, glucose builds up in the bloodstream instead of moving into the organs and cells. The body is unable to use this glucose for energy. This leads to the symptoms of type 1 diabetes.

To survive, people with type 1 diabetes must have insulin delivered by injection or a pump. All people with the disease are treated with daily insulin injections, exercise, and diet, and are trained to make multiple daily blood glucose measurements.

Symptoms: Bad to Worse

Young people with type 1 diabetes develop symptoms over a short period of time. (Adults with LADA usually take much longer to manifest symptoms.) These symptoms are usually the first signs of type 1 diabetes, or may occur when blood sugar is high:

  • Feeling tired or fatigued
  • Feeling hungry
  • Being very thirsty
  • Urinating more often
  • Losing weight without trying
  • Having blurry eyesight
  • Losing feeling or experiencing tingling in your feet

It’s hard to miss type 1 diabetes in kids—they become obviously very sick. But if the disease goes undiagnosed from early symptoms, it may be discovered in a health emergency.  A person with the following warning symptoms may be dangerously sick. They may be the first signs of type 1—or in a person with established type 1 disease, they may happen when the blood sugar is very high (see diabetic ketoacidosis, below):

  • Deep, rapid breathing
  • Dry skin and mouth
  • Flushed face
  • Fruity breath odor
  • Nausea or vomiting, unable to keep down fluids
  • Stomach pain

Such symptoms call for immediate medical attention if diabetes has not yet been diagnosed. People already under treatment should consult their doctor.

Recent studies indicate that early and effective treatment can decrease the chance of developing the complications associated with diabetes.

Fluctuations in Blood Sugar

All the above symptoms, whether more or less severe, are signs of elevated blood sugar, known as hyperglycemia—the key marker of all diabetes. When blood sugar drops below normal levels, it’s known as hypoglycemia.

In normal metabolism, beta cells respond to rising blood glucose levels throughout the day by secreting just the right amount of insulin to maintain levels in the normal range. Insulin travels through the bloodstream, carrying glucose into cells throughout the body, such as liver, muscle, and brain cells.

Cells can use this glucose immediately to satisfy energy needs, or—as in liver and muscle cells—store it in a long chain of molecules called glycogen. Glycogen can be broken down and released back into the bloodstream later if blood glucose levels drop, such as between meals or during sleep.  This may also occur in response to stress (the “flight or fight” response), to make extra energy available for the system to cope.

Maintaining good control over blood glucose is vital to ensure that cells always get enough energy, and that the brain (which relies completely on glucose for energy) functions properly. If too much insulin is secreted over a given time, blood glucose levels drop too low (hypoglycemia), and cells may not get enough glucose between meals. Hypoglycemia can lead to lethargy, convulsions, coma, brain damage, or even death.

Conversely, if not enough insulin is produced, blood glucose levels become elevated (hyperglycemia), but not enough glucose actually reaches the cells. Reacting to the low insulin signal, the muscle and liver cells seek other ways to satisfy their energy needs and start breaking down muscle and fat to form molecules called ketoacids. (Ketoacid production is not limited to diabetics. A nondiabetic on an ultra-low-carbohydrate diet may have the characteristic fruity “ketone breath” because the liver is making carbs from protein and makes ketoacids as a side effect.)

Ketoacids are the body’s response to very low insulin—a signal of starvation—and can serve as an energy source of last resort. However, as they become more concentrated in the blood, a person can develop diabetic ketoacidosis (DKA), a dangerous short-term complication that can lead to dehydration, vomiting, confusion, swelling of the brain (cerebral edema), and coma. If uncontrolled over many years, hyperglycemia causes serious damage to blood vessels, nerves, and kidneys.

It should be clear, then, that all treatment for type 1 centers on controlling the rise and fall of blood sugar. Maintaining normal blood glucose levels—the state known as euglycemia—is extremely important for long-term health, and insulin plays a dominant role.

Treating Type 1

The onset of type 1 diabetes can occur suddenly, and is marked by recurring episodes of hyperglycemia. Typically, the destruction of beta cells begins months to years or even decades before diagnosis. In fact, most people have lost most of their beta cell mass by the time they are diagnosed, and many of the remaining beta cells are not working normally. Thus little to no insulin is being produced, leading to the symptoms and ill effects of hyperglycemia.

Injected insulin has been the indispensable therapy for type 1 since its discovery in the 1920s. Of course, the formulations of insulin and methods of delivery have become ever more varied and sophisticated, especially with the recent development of the insulin pump along with fast-acting insulins. Current approaches to therapy—all of which include diet and exercise as key components—are discussed in Managing Type 1 Diabetes.


  • Type 1 diabetes is a complex disease that’s most often diagnosed in children and young people. It can be effectively treated with injected insulin but as yet there is no cure.
  • Diabetes symptoms are caused by hyperglycemia (high blood sugar) or hypoglycemia (low blood sugar). In type 1, mild symptoms always lead to severe ones if untreated. High blood sugar may also cause ketoacidosis, a dangerous short-term complication.
  • Treatment for T1D currently depends on injected insulin, delivered by a variety of ever-more sophisticated means.