Chances are good that someone you know has type 2 diabetes. According to the National Institutes of Health (NIH), over 37 million people in the United States—around 1 out of every ten people—have diabetes. And about 95% of these cases—around 35 million people—are type 2 diabetes, a chronic disorder in which the body is unable to properly make use of insulin, resulting in high blood glucose levels.

Recently, the prevalence of type 2 diabetes has increased around the world, driven, in part, by rising levels of obesity and sedentary lifestyles. In the past, type 2 diabetes was sometimes referred to as adult-onset diabetes because it mostly occurred adults. Today, however, it’s increasingly being diagnosed in children and young adults as well.

Fortunately, type 2 diabetes can be managed with lifestyle changes, blood glucose monitoring, and medications that help lower blood glucose levels.

“Just in the past decade, new classes of medications to treat diabetes have been released, which have revolutionized the arsenal of diabetes treatments,” says Yale Medicine endocrinologist Anika Anam, MD. “There have also been spectacular advances in diabetes technologies, from continuous glucose monitors to ‘closed-loop’ insulin pumps, that have helped patients manage their diabetes more effectively.”

Type 2 diabetes, also known as type 2 diabetes mellitus, is a disorder marked by higher-than-normal levels of glucose (a type of sugar) in the blood.

Glucose is the body’s main source of energy. Normally, after a person eats carbohydrate-rich food—a piece of bread, for instance—the body extracts nutrients from it, including glucose. The glucose enters the bloodstream, where it’s circulated to cells all around the body. To help the glucose enter the cells, the body uses insulin, a hormone produced by the pancreas.

In people with type 2 diabetes, the body’s cells don’t respond properly to insulin, and glucose doesn’t move efficiently from the bloodstream into the cells. This is known as insulin resistance. As a result, the level of glucose in the blood rises. Initially, the pancreas responds to high blood glucose levels by producing more insulin. This may control blood glucose levels for some time, but eventually the pancreas is not able to produce enough insulin to keep blood glucose in the normal range.

Glucose builds up in the blood, leading to high blood glucose levels, a condition known as hyperglycemia. High blood glucose can damage blood vessels and nerves, and cause a number of symptoms, such as increased urination and thirst, fatigue, blurry vision, and weakness.

Type 2 diabetes is different from type 1 diabetes, a disorder in which the body produces little to no insulin, resulting in high blood glucose levels.

Prediabetes is a condition in which blood glucose levels are higher than normal, but not high enough to be diagnosed as diabetes. People with prediabetes may not have any symptoms, but they are at increased risk for developing type 2 diabetes, as well as heart disease and stroke. In the U.S., around 1 in 3 adults has prediabetes, though the majority of them are unaware of it.

Risk factors for type 2 diabetes include:

• Family history of type 2 diabetes in a parent or sibling
• Obesity and being overweight
• Sedentary lifestyle and physical inactivity
• Prediabetes
• High blood pressure
• Polycystic ovary syndrome
• Having had gestational diabetes mellitus
• Smoking
• Metabolic syndrome
• Age (more common in adults over age 45)
• Diet (consuming processed meat, red meat, and sugary beverages, as well as low consumption of fiber)
• Certain medications, including glucocorticoids, thiazide diuretics, and atypical antipsychotics
• Exposure to certain toxins, including arsenic, bisphenol A (BPA), and pesticides
• History of heart attack or heart failure
• Low level of good (HDL) cholesterol and high triglyceride levels

In many cases, people with type 2 diabetes do not have any symptoms When symptoms are present, they may include:

• Increased urination
• Waking at night to urinate
• Increased thirst
• Feeling tired
• Weakness
• Increased appetite and hunger
• Recent unintentional weight loss
• Blurred vision
• Numbness or tingling sensation in hands and/or feet
• Frequent infections Wounds (such as foot ulcers) that heal slowly

Very high blood glucose levels can lead to a condition called hyperosmolar hyperglycemic state (HHS). HHS is a life-threatening condition marked by severe dehydration, disorientation, and loss of consciousness.

People with type 2 diabetes are at increased risk for certain medical complications, including:

• Heart disease
• Peripheral vascular disease
• Stroke
• Eye and vision problems including diabetic retinopathy, diabetic macular edema, and glaucoma
• Chronic kidney disease
• Peripheral neuropathy
• Diabetic ketoacidosis (DKA)
• Foot problems (ulcers, infections, gangrene)

To diagnose type 2 diabetes, your doctor will review your medical history, conduct a physical exam, and order blood tests.

Your doctor may begin to make a diagnosis by asking about symptoms and when they began. He or she will also ask if you have any risk factors for type 2 diabetes, such as a family history of the disease. During the physical exam, your doctor will check your weight, blood pressure, and examine your skin and abdomen.

A blood test to measure blood glucose levels is necessary to confirm diagnosis. A few different tests may be used, including:

• Hemoglobin A1C (HbA1C) test. Also known as A1C, this test measures the average blood glucose level over the previous 3 months. A1C levels of 5.7% or lower are considered normal. A1C levels between 5.7 and 6.4% are consistent with prediabetes, and diabetes is diagnosed when A1C level reaches 6.5% or above.
• Fasting plasma glucose (FPG) test. This test measures blood glucose level in patients who have been fasting for at least 8 hours. Blood glucose levels of 126 mg/dL (milligrams per deciliter) or higher indicate diabetes, while prediabetes is diagnosed when FPG levels are between 100 and 125 mg/dL. An FPG level of 99 mg/dL or lower is considered normal.
• Random plasma glucose (RPG) test. This test is used to measure blood glucose levels in people who have symptoms of type 2 diabetes. Patients do not need to fast for this test. Diabetes is diagnosed in people who have symptoms and RPG levels of 200 mg/dL or higher. 
• Oral glucose tolerance test (OGTT). This test measures how well the patient’s body processes glucose. The patient fasts for 8 or more hours, then has their blood drawn. The blood sample is analyzed to determine the fasting blood glucose level. The patient then drinks a solution containing a concentrated amount of glucose. Blood is again drawn at intervals of 1, 2, and sometimes 3 hours after drinking the glucose solution. A two-hour blood glucose level of 200 mg/dL indicates diabetes; prediabetes is diagnosed if glucose is between 140 and 199 mg/dL.

Type 2 diabetes treatment aims to keep blood glucose levels within a healthy range. Keeping blood sugar levels under control helps to relieve symptoms and lower the chances of developing complications.

Treatment involves a multipronged approach that may include:

• Patient education. Patient education about type 2 diabetes and its relationship to lifestyle habits, blood glucose monitoring, and treatment is a crucial component of treatment. Education may involve consultations with dietitians, diabetes nurses, and other diabetes specialists.
• Lifestyle changes. These include following a healthy diet and exercising regularly. People who have obesity or who are overweight should aim to lose weight, and those who smoke should quit smoking. Avoiding excessive alcohol consumption is also recommended.
• Monitoring. People with type 2 diabetes may need to monitor their blood glucose. This typically involves a finger stick with a lancet and a blood glucose monitoring device. In some cases, a continuous glucose monitoring device that frequently measures glucose levels throughout the day may be inserted under the skin. Periodic A1C tests and/or other blood tests are usually necessary.
• Medications. Many drugs that help lower blood glucose levels are available. These work in different ways, for example, by improving how cells use insulin, increasing the amount of insulin produced by the pancreas, or helping the kidneys excrete more glucose into the urine. Insulin injections may also be used to treat type 2 diabetes.
• Treating underlying conditions. It’s important that people who have type 2 diabetes treat any associated medical conditions, such as high blood pressure and high LDL cholesterol. Bariatric surgery for weight loss may also be recommended for some patients.

Once diagnosed, type 2 diabetes is a chronic condition that requires monitoring, treatment, and lifestyle changes. The outlook for people with type 2 diabetes depends, in large part, on how well their blood glucose levels are controlled.

Type 2 diabetes progresses over time and can lead to serious complications. In general, people with type 2 diabetes can improve their quality of life and prevent or slow the onset of complications by staying physically active, eating a healthy diet, controlling their body weight, and taking medications and monitoring blood glucose levels as instructed by their physician. It’s also important that people with type 2 diabetes see their diabetes doctor and eye doctor regularly for checkups­ and to monitor and treat any complications that arise.

“The Yale Diabetes Center is a regional center for expertise in management of type 1 and type 2 diabetes,” says Dr. Anam. “Yale offers a team-based approach with physicians, nurse practitioners, and nutritionists to provide state-of-the-art care, incorporating the latest medical innovations and diabetes technology tailored to each patient. In addition, there are ongoing research studies for type 2 diabetes and obesity to help advance our understanding of the mechanisms underlying this disease and ways to improve treatment.”

Visit the Yale Medicine Diabetes Content Center for more diabetes-related articles and videos.