Type 2 diabetes, which is different from type 1 and gestational diabetes, accounts for around 95 percent of all diabetes cases worldwide. In 2018, 10.5 percent of the U.S. population had diabetes, amounting to 34.2 million people of all ages. Of those with diabetes, 32.6 million had type 2 diabetes, and just 1.6 million had type 1 diabetes, including around 187,000 children and adolescents. 

In addition, 88 million American adults—or one in three people over the age of 20—had prediabetes, but most were unaware of it, according to the Centers for Disease Control, which also points out that addressing diabetes can prevent or delay other related health problems, including heart disease, kidney disease, and vision loss.

What causes type 2 diabetes?

Type 2 diabetes occurs when your body doesn’t produce enough insulin or use it properly, and your blood glucose levels increase as a result. Insulin is a hormone made by beta cells in the pancreas, and it acts like a key that “unlocks” the cells in your brain, liver, muscles, fat, and other tissues to allow the glucose, or sugar, that’s in your blood to enter them. 

Glucose comes from the food you eat, and it’s what fuels your body. When you eat, your blood glucose levels increase, triggering the release of insulin. Once the insulin “unlocks” the cells so the glucose can move from the blood to the cells, your blood glucose levels go back down. 

If your pancreas doesn’t make enough insulin (beta cell dysfunction), or your body doesn’t use it properly (insulin resistance), too much glucose stays in the blood—a condition known as hyperglycemia—and the body’s cells don’t get enough of it for fuel. Beta cell dysfunction and insulin resistance aren’t the same thing, but they influence each other in highly complex ways to cause type 2 diabetes.

Beta cell dysfunction

Beta cell dysfunction is characterized by the inability of these cells in the pancreas to produce enough insulin to clear the blood of glucose. Beta cell dysfunction has a range of causes, including genetics, inflammation due to obesity, and immune cells that infiltrate the pancreas and secrete cytokines that cause the death of beta cells. Additionally, persistently high blood glucose levels due to a poor diet, for example, can cause the beta cells to become exhausted so they don’t produce enough insulin. Frequent fasting and states of starvation may also affect beta cell function by producing hypoglycemic (low blood sugar) states that may prime the cells to respond less optimally to hyperglycemic states. 

Insulin resistance

Insulin resistance occurs when the cells in your body don’t respond very well to insulin and don’t take up enough glucose from the blood to lower your blood sugar levels. To compensate for insulin resistance, your pancreas increases its production of insulin, causing a condition known as hyperinsulinemia. Too much insulin in the blood results in weight gain, which, in turn, increases insulin resistance and the overproduction of insulin to compensate. 

Insulin resistance compounds beta cell dysfunction—at some point, the beta cells become exhausted and can no longer meet the higher demand for insulin created by the insulin resistance. This results in hyperglycemia, which eventually leads to type 2 diabetes. Insulin resistance is an important factor in the development of obesity, cardiovascular disease, nonalcoholic fatty liver disease, metabolic syndrome, and, in women, polycystic ovary syndrome, or PCOS.

Acquired and genetic causes of type 2 diabetes

The vast majority of cases of type 2 diabetes are acquired, which means that they’re the result of things like:

  • Physical inactivity
  • Poor nutrition
  • High-sodium diets
  • Obesity
  • Overweight or extra belly fat
  • Aging

Certain genes may increase the risk of developing type 2 diabetes, which often runs in families. Some genes may predispose you to obesity, which increases your risk of type 2 diabetes, and genetic mutations—including those that cause cystic fibrosis, PCOS, and hemochromatosis—may also play a role in its development, including.

How are prediabetes and type 2 diabetes diagnosed?

Prediabetes is a precursor to type 2 diabetes and is characterized by blood sugar levels that are higher than normal—but not high enough to be diagnosed as diabetes. Four tests are commonly used to diagnose prediabetes and type 2 diabetes. 


This simple blood test measures your average blood sugar levels over the past three months.

Normal: less than 5.7 percent

Prediabetes: 5.7 to 6.4 percent

Diabetes: 6.5 percent or higher

Fasting plasma glucose (FPG)

This blood test is typically performed first thing in the morning, after at least eight hours of fasting. 

Normal: less than 100 mg/dL

Prediabetes: 100 mg/dL to 125 mg/dL

Diabetes: 126 mg/dL or higher

Oral glucose tolerance test (OGTT)

This test involves measuring your blood sugar levels before you drink a special sweet drink. Then, two hours after drinking it, your blood is tested again to see how your body processes blood glucose.

Normal: less than 140 mg/dL

Prediabetes: 140 mg/dL to 199 mg/dL

Diabetes: 200 mg/dL or higher

Random plasma glucose test (RPGT)

Also called the casual plasma glucose test, this test checks your blood at any time of day, and it’s used for people who have severe diabetes symptoms. If the test shows a blood sugar level of 200 mg/dL or higher, you’ll be diagnosed with diabetes. 

Symptoms of prediabetes and type 2 diabetes

Prediabetes doesn’t usually produce symptoms, although some people with prediabetes may experience symptoms of type 2 diabetes, which include:

  • Frequent urination
  • Feeling very thirsty or very hungry
  • Extreme fatigue
  • Injuries that heal slowly
  • Blurred vision
  • Tingling, numbness, or pain in the hands or feet

Symptoms of type 2 diabetes typically occur gradually over time. In some cases, people with type 2 diabetes have no symptoms at all. 

Complications of type 2 diabetes

Left untreated or inadequately treated, type 2 diabetes can cause a number of serious health problems. 

Diabetic neuropathy

Neuropathy is a form of nerve damage that occurs in about half of all people with diabetes. Two common types of diabetic neuropathy are peripheral neuropathy, which causes pain, numbness, tingling, or weakness in the hands or feet, and autonomic neuropathy, which affects the nerves that control the functions of the intestinal tract, bladder, genitals, and other organs. 

Skin problems

Bacterial and fungal infections of the skin are a common complication of type 2 diabetes. Other skin problems associated with diabetes include: 

  • Localized itching caused by a yeast infection, dry skin, or poor circulation 
  • Light brown, scaly patches known as diabetic dermopathy
  • Tan or brown raised patches known as acanthosis nigricans

Eye problems

Type 2 diabetes increases your risk for glaucoma and cataracts. It may also cause diabetic retinopathy, which can lead to blurred or blocked vision, detached retina, or vision loss.

Kidney disease

Uncontrolled or poorly controlled blood sugar, combined with high blood pressure, may cause kidney disease, which can lead to kidney failure and the need for dialysis or a transplant.

Cardiovascular disease

Cardiovascular disease is the number one cause of death in people with diabetes

Diabetes doubles the risk of heart disease or stroke compared to people without diabetes, and it increases the risk of atherosclerosis (the narrowing of the arteries), heart failure, and arrhythmias (irregular heartbeats.) Diabetes also increases your risk for high blood pressure, which also contributes to cardiovascular disease.

How to reduce your risk of type 2 diabetes or its complications

Whether you have type 2 diabetes and wish to reduce your risk of complications or you don’t have diabetes and want to prevent it, reducing the risks is largely a matter of making important lifestyle changes to keep your blood sugar at healthy levels. These include:

  • Getting regular exercise
  • Eating a nutritious diet that limits unhealthy carbs and excessive sugar
  • Quitting smoking
  • Avoiding alcohol or drinking in moderation, which is defined as no more than one drink per day for women and no more than two drinks per day for men
  • Managing your stress
  • Properly monitoring your blood sugar daily if you have type 2 diabetes
  • Taking diabetes medications as directed by your physician

You should get screened for diabetes every two years, starting at age 35, if you’re overweight (BMI of 25 to 29) or obese (BMI of 30 or higher) and have no symptoms of diabetes. Asian Americans with a BMI of 23 or higher are included in this group, as are people who have a family history of diabetes and those who belong to racial and ethnic minorities with a higher prevalence of type 2 diabetes, including American Indian, Alaska Native, Asian, Black, Hispanic, Native Hawaiian, and Pacific Islander populations.

Take control of your diabetes risk with Forward

As your primary care provider, Forward focuses on the prevention, treatment, and management of diseases like diabetes, heart disease, and cancer. Our doctor-led healthy heart program, weight-loss and stress management clinics, and cancer prevention program are open to all Forward members and include genetic and blood testing as well as a personal prevention or management plan, ongoing support and monitoring, and 24/7 app-based access to your personal care team. Forward helps you take control of your health and stay informed and motivated to make lifestyle changes that can help you live a longer, healthier life.

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