Type 1 Diabetes Mellitus

Type 1 diabetes is a lifelong condition defined by the inability to produce insulin and requiring daily insulin replacement.

Type 1 diabetes (T1D) is an autoimmune disease in which the body's immune system mistakenly destroys insulin-producing cells in the pancreas, leading to a lifelong inability to produce insulin and requiring daily insulin replacement.

In normal metabolism, after eating food that contains carbohydrates, digestion breaks them down into glucose (sugar), which enters the bloodstream and raises blood sugar levels. The pancreas detects this increase and releases a hormone called insulin into the bloodstream. All cells need glucose as a source of energy to function. Insulin signals cells throughout the body (especially in muscle, fat, and liver cells) to take in that glucose from the bloodstream. It also signals the liver to stop releasing glucose and convert any excess glucose into a storage form called glycogen. These actions lower the blood sugar level back to a normal range.

Between meals, during physical activity, or while sleeping, your body uses glucose for energy, causing blood sugar levels to drop. Your pancreas detects this decrease and releases a different hormone called glucagon. Glucagon signals the liver to break down its stored glycogen back into glucose. It also prompts the liver to make new glucose from other substances. The liver then releases this glucose into the bloodstream. These actions increase the blood sugar level back to a normal range.

The pancreas constantly monitors blood sugar and uses these two hormones, insulin and glucagon, to signal the liver to keep the blood sugar level stable.

The immune system in a person with diabetes makes antibodies that destroy the insulin-producing islet beta cells in the pancreas. The pancreas then fails to make insulin. Without insulin, blood sugar increases and cannot be delivered to the muscles, brain, and other organs where it is needed for energy.

Type 1 diabetes is an autoimmune disease. The body's immune system mistakenly identifies the insulin-producing beta cells in the pancreas as harmful invaders and attacks and destroys them. The pancreas loses its ability to produce insulin and glucose from food builds up in the bloodstream instead of entering cells for energy. This can lead to high blood sugar (hyperglycemia: hyper=high + glyc=glucose + emia=blood).

About 2 million people in the US have type 1 diabetes. Of those, about 304,000 are children and adolescents younger than age 20, and 1.7 million are adults older than age 20.

It is estimated that 5 million people in the US will have type 1 diabetes by 2050.

Type 1 diabetes is primarily an autoimmune disease with a strong genetic predisposition. Instead of being purely hereditary or solely acquired, it arises from a combination of inherited genetic risk factors as well as environmental triggers.

People inherit certain genes (such as HLA variants) that increase susceptibility to type 1 diabetes, but not everyone with the genes will develop diabetes. An environmental trigger such as a dietary factor, or exposure to a virus or toxin, may activate the immune system causing it to mistakenly destroy insulin-producing beta cells in the pancreas. This autoimmune process is why type 1 diabetes isn't directly "passed down" like a purely genetic disease.

Type 1 diabetes is caused by autoimmune destruction of pancreatic beta cells that produce insulin. It is not known why this autoimmune destruction happens. However, some potential triggers include:

• Genetics, including family history and the prenatal environment of the mother
• Exposures to chemicals, especially endocrine disruptors. These disruptors can be found in plastics, pesticides, and water contaminated with PFAS and dioxins
• Viral infections may trigger the autoimmune process
• Early or late introduction of certain foods to infants has been shown to trigger type 1 diabetes in research studies. Introducing fruit before 5 months of age or introducing grains after 7 months may increase the risk of diabetes. Research also shows that breastfeeding may reduce these risks
• Both early (before 4 months) and late (after 6 months) introduction of solid foods to infants are associated with an increased risk of type 1 diabetes especially in those who are genetically susceptible. Late exposure to rice and oat foods carries the strongest risk. Breastfeeding during the introduction of solids reduces type 1 diabetes risk and is especially critical when introducing wheat and barley containing foods. Longer breastfeeding and delayed introduction of bottle-feeding may also be protective.

However, the underlying cause of type 1 diabetes is not fully known.

Risk factors for developing type 1 diabetes may include the following:

• Prenatal exposures include maternal preeclampsia or metabolic syndrome
• Environmental exposures include chemicals, including those found in plastics, foods, and water (PFAS and dioxins)
• With food:
  • introduction of gluten, casein (the protein in dairy) or fruit before 4 months of age
  • late introduction to grains (gluten, oat, and rice) and casein after 7 months of age
• Viral infections, such as Epstein-Barr virus (the virus that causes mononucleosis), coxsackie, cytomegalovirus
• Living in a northern climate is a risk factor that has not been fully explained

Type 1 diabetes is an autoimmune disease where the body's immune system destroys the insulin-producing beta cells in the pancreas. Little or no insulin is manufactured, making daily insulin replacement either by injections or by a pump essential for survival. It often develops suddenly in childhood or adolescence but it can occur at any age. Type 1 diabetes is influenced by genetics, but also usually has an environmental trigger.

Type 2 diabetes is primarily a metabolic disorder caused by the body’s inability to properly respond to insulin (also known as insulin resistance) and/or the gradual decline in insulin production over time. Type 2 diabetes usually develops gradually in adulthood and is linked to genetics, obesity, inactivity, and aging. It makes up 90–95% of all diabetes cases, and is often managed initially with lifestyle changes in diet and exercise, oral medications, and sometimes insulin.

Type 1 diabetes often presents suddenly, but early symptoms may include the following:

• Frequent urination. Polyuria (poly=many + uria=urine) is the most common symptom of new onset type 1 diabetes. Excess sugar in the blood (hyperglycemia) pulls fluid from tissues into the blood stream to dilute that high concentration of sugar. The kidneys respond to the increased fluid load by increasing urine output, leading to unusually frequent urination. Children may develop new nighttime bedwetting, or their diapers may feel unusually heavy with urine.
• Excessive thirst. Polydipsia (poly=many + dipsia=thirst) is directly related to the frequent urination, as the body tries to replace the water lost in the urine.
• Extreme fatigue and weakness. Because cells cannot use glucose for energy without the presence of insulin, persistent exhaustion occurs.
• Weight loss. The body breaks down muscle and fat for energy when glucose cannot be used. Rapid weight loss is common and occurs even with normal or increased food intake.
• Increased hunger. Polyphagia (poly=many +phagia=swallowing or eating). Even with increased appetite and higher blood glucose, cells cannot access glucose for energy without insulin, leading to persistent hunger.
• Blurred vision. High blood sugar causes shifts of fluid inside the lenses of the eye, making it difficult to focus. When blood sugar levels are controlled and return to normal, the vision issues usually resolve.
• Slow-healing wounds or infections. High blood glucose affects the immune system, increasing the chance of infection and delaying the ability of the body to heal.
• Diabetic ketoacidosis (DKA) occurs when cells can’t use glucose and the liver breaks down fat for energy. This can be a life-threatening emergency and some people with the new diagnosis of type 1 diabetes present in DKA. Symptoms may include any or all of the following:
  • dehydration
  • rapid shallow breathing
  • nausea and vomiting
  • abdominal pain
  • sweet or fruity-smelling breath
  • confusion

The initial diagnosis of type 1 diabetes is usually made by a primary healthcare provider, or in the emergency department or urgent care.

Often, the healthcare provider makes a preliminary diagnosis of diabetes based on history of polyuria, polydipsia, and weight loss. Blood tests are then ordered to confirm the diagnosis of diabetes.

Diabetes blood test criteria levels

The American Diabetic Association recognizes the following blood test criteria to make the diagnosis of diabetes. Please note that they do not distinguish between type 1 or type 2.

1. Fasting plasma glucose (fasting blood sugar). Nothing to eat or drink for 8 hours prior to the blood test

• Diabetes: 126 mg/dL (7.0 mmol/L) or higher
• Prediabetes: 100-125 mg/dL (5.6-6.9 mmol/L)
• Normal: Less than 100 mg/dL (5.6 mmol/L)

2. Oral glucose tolerance test (OGTT). For this test, the patient fasts overnight, has blood drawn for a fasting glucose reading, then drinks a glucose solution, and has blood sugar levels measured again at regular intervals for the next two hours.

• Diabetes: 200 mg/dL (11.1 mmol/L) or higher at 2 hours
• Prediabetes: 140-199 mg/dL (7.8-11.0 mmol/L) at 2 hours
• Normal: Less than 140 mg/dL (7.8 mmol/L) at 2 hours

3. Hemoglobin A1C (HbA1c) test. This blood test reflects the average blood sugar level over the past couple months and may not be accurate if there has been a recent spike in blood sugars.

• Diabetes: 6.5% or higher
• Prediabetes: 5.7-6.4%
• Normal: Less than 5.7%

4. Random plasma glucose test (random blood sugar). This test is done at any time, regardless of when the patient last ate.

• Diabetes: 200 mg/dL (11.1 mmol/L) or higher in a patient with classic symptoms of hyperglycemia (frequent urination, increased thirst, and unexplained weight loss), or hyperglycemic crisis (like DKA)

Approximately 25% of new type 1 diabetes patients present very ill with symptoms of DKA that can also include nausea, vomiting, abdominal pain and sweet, fruity breath odor, dehydration and confusion. Emergent care is required to treat these patients.

Adult and pediatric endocrinologists, specialists in treating hormonal disorders and disorders of the endocrine system, manage patients with diabetes.

Type 1 diabetes cannot be cured, but it can be controlled. People with type 1 diabetes require regimens of injectable insulin because their pancreas does not produce enough to meet the body’s needs. In addition education about foods and food intake is an important part of the treatment of patients with type 1 diabetes.

Insulin regimens are individualized to each patient’s needs. There are short-acting and long-acting injectable insulins, as well as insulin that can be delivered by a pump worn by the patient.

Patients are taught how to dose their insulin to match their caloric intake and to use a diet that does not cause high spikes in blood sugar levels. Some patients measure their blood glucose routinely during the day, while others wear devices that automatically measure blood glucose.

The goal is to match the insulin requirements of the body with the calories that are eaten. Too little insulin and blood sugars spike. Too much insulin and blood sugars drop.

Ideally, the diet and insulin treatment regimen in patients with diabetes will result in the same blood sugar levels as a nondiabetic patient.

There is no universal type 1 diabetes diet. Effective management requires strategic carbohydrate counting, balanced nutrition, and routine insulin adjustment to meet the patient’s needs.

People with type 1 diabetes must match insulin doses to carbohydrate intake to maintain stable blood sugar levels. The following are some of the strategies that are recommended:

• Counting carbohydrates (carbs) in meals/snacks (using labels or apps) to calculate insulin needs
• Prioritizing complex carbs like whole grains and vegetables, instead of simple sugars to minimize blood sugar spikes
• Balancing meals with protein, healthy fats, and fiber to slow glucose absorption during digestion to prevent blood sugar spikes
• Timing insulin based on food (e.g., pre-bolusing for high-glycemic foods)
• Avoiding prolonged fasting to prevent hypoglycemia

A diet that is consistent allows insulin dosing that can be predictable. A dietitian is helpful to individualize meal plans and to account for other factors that affect blood sugar levels such as activity, stress, and hormone cycles.

The goal is to have a flexible diet plan without compromising blood sugar control.

The impact of exercise on blood sugar levels is complicated. Depending upon the intensity, duration, type of activity, and time of day, blood sugar levels may go up or down.

Most commonly, aerobic exercises like walking, running, or cycling will lower blood sugar levels as muscles absorb sugar for energy. If insulin levels aren’t adjusted, there is the potential for hypoglycemia during or after exercise.

Less commonly, high intensity exercises like sprinting, weightlifting, or anaerobic training like HIIT (high intensity interval training) can trigger stress hormones in the body such as cortisol and adrenalin. These hormones trigger the liver to move glucose from storage into the blood stream causing blood sugar levels to rise.

Patients with diabetes who begin an exercise program should involve their treatment team, including their healthcare provider and their dietitian, to provide guidance regarding type of exercise, duration of exercise, and how to monitor and treat blood sugar levels.

Chronic complications of diabetes develop over time because of chronically high blood sugar levels that damage blood vessels and nerves throughout the body. 

Complications affecting large blood vessels are due to an increased risk of atherosclerosis (hardening and narrowing of arteries). This can lead to:

• High blood pressure
• Heart attack (myocardial infarction)
• Stroke
• Peripheral artery disease (PAD) affects the arteries that supply blood to the limbs, especially the feet and legs. This may lead to poor circulation, skin breakdown, recurrent infection, and potentially amputation

Complications affecting small blood vessels

• Kidney disease (diabetic nephropathy) impairs the ability to filter waste from the blood. Symptoms include edema (swelling) due to lost protein in the urine, frequent urination, and foamy urine. It can progress to kidney failure requiring dialysis or kidney transplant 
• Eye damage (diabetic retinopathy) occurs when high blood sugar levels damage the blood vessels in the retina, the nerves in the back of the eye that allow sight to be transmitted to the brain. This damage leads to progressive blurred vision and vision loss
• Nerve damage (diabetic neuropathy) when high blood sugars cause nerve damage throughout the body. Peripheral neuropathy in the arms and legs can cause pain, numbness, and tingling in the feet and hands. It can also affect balance and position sense. Autonomic neuropathy affects the nervous system that are not under conscious control such as blood pressure, stomach function, sexual function, and bladder control

Other chronic complications include the following:

• Diabetes can weaken the immune system, increasing the risk of infections
• Nerve damage and poor circulation increase the risk of foot ulcers, infections, and can lead to amputation
• Skin infections and gum disease
• Hearing impairment
• Osteoporosis leading to an increase risk of fractures
• Increased risk of cognitive impairment, including dementia and Alzheimer’s disease

Can you live a full life with type 1 diabetes?

A full, vibrant life with type 1 diabetes is the goal of treatment. Modern technology such as continuous glucose monitors and insulin pumps, personalized care with a treatment team, and proactive management allows people with type 1 diabetes to not be limited in their choice of life options. They are free to choose careers, relationships, athletics, hobbies, and passions like anyone else without diabetes. Present day treatment plans aiming for tighter glucose control have dramatically allowed adults with well-managed type 1 diabetes to live comfortably into their 70s and older. While this is 10–12 years less than average, that difference is shrinking because of newer insulin therapies, earlier complication screening, and technology innovation.

There are benefits to consistent glucose monitoring, maintaining access to healthcare, and working with a supportive diabetes treatment team.

Is type 1 diabetes curable?

Type 1 diabetes is presently incurable. Management remains lifelong insulin therapy requiring injections and pumps in conjunction with routine blood glucose monitoring. Newer technology exists including continuous glucose monitoring systems, smart insulin pens, and closed loop “artificial pancreases” but they do not treat the cause of type 1 diabetes, the autoimmune destruction of pancreas cells that produce insulin.

Research is ongoing to find a cure. Areas being explored include stem cell transplant, disease modifying immunotherapy, and gene editing.

Type 1 diabetes cannot be prevented. The underlying cause of the autoimmune response remains unknown.

Pregnant women with type 1 diabetes are considered high-risk. Tight blood sugar control is especially important throughout the pregnancy to minimize the risk of pre-eclampsia, premature labor, and having a large baby. Routine prenatal care is important to monitor the health of both the mother and fetus.