What Is Type 2 Diabetes? Symptoms and Causes

Type 2 diabetes (T2D) is a disease that develops when your blood sugar levels are too high. This may be caused by a combination of lifestyle choices (poor dietary habits, lack of exercise) and genes passed down through family members.

Learning about what causes T2D, the symptoms to look for, and how it’s diagnosed can help you get the treatments you need to live a healthy life. T2D is also associated with several health complications, so it’s important to properly manage your blood sugar levels.1

Who Develops Type 2 Diabetes?

T2D can affect anyone, but it’s mainly diagnosed in middle-aged and older individuals. The Centers for Disease Control and Prevention (CDC) state that more than 37 million people in the United States have diabetes, and between 90 to 95 percent of them have T2D. The disease typically develops in people ages 45 or older, but in recent years it’s become more common in children, teenagers, and young adults.1

Risk Factors for Type 2 Diabetes

Certain groups of people are at a higher risk of developing T2D compared to others. People who are of Hispanic/Latino, African American, Asian American, American Indian, or Pacific Islander descent are at a higher risk of T2D.

If a close family member has the disease, such as a parent or sibling, you’re also more likely to develop it yourself.

Other risk factors for T2D include:2

  • Having prediabetes, or elevated blood sugar levels that aren’t high enough to be diagnosed as diabetes
  • Getting physical exercise less than three times per week
  • Being overweight
  • Having non-alcoholic fatty liver disease
  • Previously having gestational diabetes (diabetes that develops during pregnancy) or giving birth to a baby weighing 9 pounds or more

What Causes Type 2 Diabetes?

When you eat food, your body breaks it down into its preferred form of sugar known as glucose. Your body’s cells use glucose for energy. For glucose to enter your cells, it needs help from the hormone insulin. Insulin is made by specialized cells known as beta cells in your pancreas.1

When you eat, glucose triggers your pancreas to release insulin, which enters your bloodstream. In T2D, your cells become resistant to insulin and can’t use it properly. This means there’s more glucose in your blood, causing your blood sugar level to rise. Your pancreas tries to compensate for the rise in blood sugar by making more insulin, but eventually, it can’t keep up with demand.

As a result, you’ll need to be treated with medications that help your cells become more sensitive to insulin, stop your liver from making more glucose, and help your kidneys clear extra glucose out of your body. In more severe cases, your doctor may prescribe insulin therapy along with these medications to help boost their effects.

Symptoms and Signs of Type 2 Diabetes

Since T2D develops slowly over time as your blood sugar level continues to rise, you may not notice any symptoms at first. In fact, they may take years to develop. T2D symptoms are signs of high blood sugar, which include:5

  • Extreme thirst and hunger
  • Feeling extremely tired
  • Feeling a tingling or numb sensation in your hands or feet
  • Having blurry vision
  • Losing weight without trying to
  • Having more infections than normal
  • Having sores or wounds that heal slowly

What’s the Difference Between Type 1 and Type 2 Diabetes?

While they’re both types of the same disease, type 1 diabetes (T1D) and T2D differ quite a bit. Both diseases involve high blood sugar levels, but T1D occurs when your pancreas can’t make any insulin. Doctors and researchers believe that T1D is a form of autoimmune disease in which the body’s immune system recognizes the beta cells in the pancreas as foreign. It then attacks and kills them so they can no longer make insulin.3

T1D tends to develop more often in children, teenagers, and young adults. It’s also much less common than T2D, accounting for only 5 to 10 percent of diabetes cases. T1D is mainly treated with insulin since your body can’t make it on its own. You may use an insulin pump or take insulin shots using a needle and syringe.

There is also an increased risk of complications in T1D compared to T2D. One of these is diabetic ketoacidosis (DKA), which is a serious complication that requires immediate medical attention. Symptoms of DKA include extreme thirst and frequent urination.4

How Is Type 2 Diabetes Diagnosed?

T2D is diagnosed using a few different tests that look at your blood sugar levels. These tests are typically done in your doctor’s office or a medical laboratory and testing center. If you’re experiencing symptoms of T2D, your doctor will likely order some tests, including your hemoglobin A1c (HbA1c), a fasting blood sugar value or oral glucose tolerance test (OGTT).6

Hemoglobin A1c Test

An HbA1c test is one of the most common tests used to diagnose T2D. It measures your average blood sugar level over the past three months, which gives your doctor an idea of how high your levels normally are. You do not need to fast (not eat) before an HbA1c test.

Glucose, your body’s preferred form of sugar, attaches to hemoglobin, the protein in red blood cells that’s responsible for carrying oxygen. It’s normal to have some glucose attached to your hemoglobin, but people with higher blood sugar levels tend to have more. An HbA1c test measures how much glucose is attached to the hemoglobin in your red blood cells, and gives it as a percentage. These results may also be given to you in the same measurements given on your glucose monitor, in milligrams per deciliter of blood (mg/dL).7

  • Normal — estimated average blood glucose of 99 mg/dL or below (HbA1c 5.7% or below)
  • Prediabetes — estimated average blood glucose of 100 to 125 mg/dL (HbA1c 5.7% to 6.4%)
  • Diabetes — estimated average blood glucose of 126 mg/dL or above (HbA1c 6.4% or above)

Factors that can affect your HbA1c level include:

  • Taking certain medications, such as HIV medications or opioid pain relievers
  • Having severe anemia (low iron in your blood), kidney failure, or liver disease
  • Blood transfusions or blood loss
  • Having a less common type of hemoglobin found in people of Mediterranean, Southeast Asian, or African descent
  • Having a blood disorder, such as thalassemia or sickle cell anemia
  • Early or late pregnancy

Oral Glucose Tolerance Test

T2D is caused by your cells not being able to use insulin well to take glucose from your blood to make energy. An oral glucose tolerance test (OGTT) tests how well sugar moves from your bloodstream into your body’s tissues, such as fat and muscle. Higher blood sugar levels during an OGTT indicate that your cells can’t properly take up glucose from your blood.8,9

Before an OGTT, you’ll fast overnight to avoid any spikes in your blood sugar. The morning of your test, you’ll have a blood sample taken to measure your fasting blood sugar level. (A level over 126 mg/dL would already suggest you have T2D.) You’ll then drink a very sweet glucose solution and wait for a few hours. During that time, you’ll have more blood samples taken at one hour, two hours, and maybe three hours after you drank the glucose solution. Your blood sugar levels at these different time points will tell your doctor whether you have diabetes. After two hours, you will have your results:

  • Normal — blood sugar level of 140 mg/dL or lower
  • Prediabetes — blood sugar level of 140 to 199 mg/dL
  • Diabetes — blood sugar level of 200 mg/dL or higher

Complications from Type 2 Diabetes

Over time, high blood sugar levels from T2D can damage your body’s blood vessels and nerves, creating other health complications. These can affect several parts of the body, including your eyes, kidneys, and nerves in your hands and feet. T2D also doubles your risk of heart disease and stroke compared to people without diabetes.

Eye Problems from Type 2 Diabetes

People with T2D may develop eye problems, such as diabetic retinopathy (DR), glaucoma, or cataracts. DR affects the retina (the light-sensitive tissue at the back of the eye), which can lead to blurry vision, floating dark spots (floaters), or vision loss. Glaucoma causes pressure to build up in the eyes, which can damage the optic nerve (connects to the retina to send images to the brain). Cataracts cause clouding of the lens that covers your eyes, leading to blurry vision or seeing double.

To avoid these complications or to get prompt treatment for them, be sure to go to regular eye check-ups — your eye doctor will monitor you for any eye diseases when living with T2D.10

Kidney Problems from Type 2 Diabetes

High blood sugar levels from T2D can also damage the delicate blood vessels in the kidneys that are responsible for filtering waste and excess fluid from the body. This is known as diabetic nephropathy. If left untreated, it can progress to chronic kidney disease (CKD). This disease affects around 33 percent of adults with diabetes. Eventually, your kidneys may become too damaged to function on their own, which can lead to kidney failure. Your doctor may regularly test your blood and urine for any signs of CKD, since you typically don’t notice symptoms until the disease has progressed.11

Nerve Problems from Type 2 Diabetes

Many people with T2D also have nerve problems, known as diabetic neuropathy. High blood sugar and triglyceride (fat) levels can cause nerve damage over time, affecting different parts of the body.

The most common type of nerve damage is peripheral neuropathy, which affects around half of people with diabetes. This condition affects the nerves in the legs and feet, and sometimes the arms and hands. You may notice a painful, numb, or “pins and needles” tingling sensation.12

Autonomic neuropathy occurs when the nerves that control your internal organs are damaged. These control your digestive system, heart rate, blood pressure, sweat glands, bladder, and sex organs. You may notice a range of symptoms depending on what organs are affected.13

Preventing Type 2 Diabetes

Even if you’re at an increased risk of developing T2D, the condition can be prevented. The CDC recommends making important lifestyle changes that not only help prevent diabetes but can help you lead a healthier life in general. Making these changes is especially important if you have prediabetes because they can help prevent the progression to T2D.14

You can help prevent and even reverse your risk of T2D by losing 5 to 10 percent of your body weight. For example, if you weigh 240 pounds, you would need to lose around 12 to 24 pounds. To do this, you can make healthier food choices. Try to choose fewer foods that are processed or high in sugar or trans fats. Instead, you can add:

  • Fruits and non-starchy vegetables
  • Lean proteins like eggs, chicken, fish, turkey, or tofu
  • Unsweetened beverages and water
  • Whole grains like steel-cut oatmeal, brown rice, and whole grain bread

Getting active can also help you lose weight and feel better overall. When starting an activity goal, it’s best to start small. You can start by choosing your favorite activity that raises your heart rate and set a goal to do it three times a week. As you get more comfortable, you can increase the number of days per week and the length of time you’re active. Choose activities that you enjoy, like walking, biking, swimming, or dancing.

Together, these lifestyle changes can help you prevent T2D and improve your overall health.

Resources for Living with Type 2 Diabetes

If you’re living with T2D, there are many resources available to help you navigate through a diagnosis, treatment, and living with the disease.