Type 2 diabetes is a chronic disease in which your body is unable to regulate the levels of glucose, a type of sugar, in your blood. Type 2 diabetes usually progresses over time and can lead to many serious complications. Type 2 diabetes can be treated with medication and lifestyle changes such as weight loss, exercise, and diet changes. In some early cases of type 2 diabetes, the disease can be reversed. Symptoms vary among people with type 2 diabetes, but common symptoms include intense hunger and thirst, fatigue, frequent urination, blurry vision, irritability, slowed healing, numbness or tingling in the extremities, and frequent yeast infections.
When you eat, your body converts carbohydrates (found in grains, potatoes, fruit, vegetables, dairy, beans, and sweets) into glucose, a form of sugar the body needs for fuel. Glucose is carried to every cell in the body by the bloodstream. The pancreas makes a hormone called insulin. Insulin is necessary to allow cells to take in glucose from the bloodstream and regulate how much glucose remains in your blood.
In the early stage of type 2 diabetes, the cells of the body become less sensitive to insulin; this stage is called insulin resistance. At first, the pancreas compensates by making more insulin. However, over time, insulin resistance grows, and the pancreas cannot make enough insulin. Cells can no longer take in glucose and begin to starve. Blood sugar levels rise, causing damage to nerves, blood vessels, and organs. The higher blood glucose levels are, and the longer they remain high, the more damage they do.
Some people are more likely than others to develop type 2 diabetes based on the genes they inherited from their parents. For instance, people with a family history of diabetes and people with African, Asian, Native American, or Pacific Islander ancestry have an increased risk for developing type 2 diabetes. Age is another factor, with type 2 diabetes being most common among those 45 and older. However, lifestyle and health factors play a major role in the development of type 2 diabetes. Being overweight or obese and not getting enough physical activity are important factors that raise the risk for type 2 diabetes. Read more about causes of type 2 diabetes.
As early as 1500 B.C., Egyptians wrote about a disease that caused a “great emptying of urine.” In the first century, Greek physician Aretaeus the Cappadocian originated the term diabetes, which in Greek means “siphon.” In ancient India, doctors referred to diabetes as madhumeha, or “honey urine,” because they noticed ants were attracted by the urine of people with diabetes. Between the years 400 and 500, Indian physician Sushruta and surgeon Charaka identified what we now know as type 1 and type 2 diabetes. Ancient treatments for diabetes — which included oil of roses, opium, and green dates — were unsuccessful, and diabetes was invariably fatal. In the 11th century, diabetes gained a second name — mellitus, which is Latin for “honey.” This term refers to the diagnostic practice at the time of physicians tasting urine for clues about disease. Diabetes mellitus is still the technical name for type 2 diabetes, although it is not used as commonly.
In 1869, young German pathologist Paul Langerhans identified the cells in the pancreas that produce insulin and several other hormones. Today these clumps of cells are known as the islets of Langerhans. In 1889, Lithuanian physiologist Oskar Minkowski and German physician Josef von Mering performed experiments on dogs, demonstrating that removing an animal's pancreas resulted in it developing diabetes. English physiologist Edward Albert Sharpey-Schafer discovered in 1910 that the pancreas produces insulin in healthy people but not in diabetics. Finally, in 1921, a team of Canadian researchers (Dr. Frederick Banting, Dr. Charles Best, Professor J.J.R. Macleod, and Dr. James Collip) at the University of Toronto proved conclusively that deficiency of insulin causes diabetes, and injecting insulin reverses the symptoms of diabetes. Banting’s team tested insulin injections on themselves, then successfully tried them on people with diabetes. They were awarded the 1923 Nobel Prize in Physiology or Medicine for their discoveries.
Insulin became available in the United States in 1923, commercially produced by Eli Lilly and Company. Insulin was derived from animals. At first, only rapid-acting insulin was available, and diabetic people had to be awakened at night for periodic injections. Over the next four decades, insulin products became purer, more stable, and longer-acting. In the 1980s, recombinant DNA biotechnology made human-derived insulin available. Human-derived insulin products worked better, and new insulin products continue to improve in effectiveness. Better syringes, insulin pumps, and other delivery methods have also continued to improve.
In the 1990s, new classes of drugs became available. These medications work in various ways to make cells more sensitive to insulin and lower blood glucose levels. Among the new drug classes were biguanides such as metformin; sulfonylureas such as glyburide (sold under the brand names DiaBeta and Micronase) and Amaryl (glimepiride); and glitazones such as Actos (pioglitazone) and Avandia (rosiglitazone). In the 21st century, new medications have included glucagon-like peptide-1 receptor agonists like exenatide (sold under the brand names Byetta and Bydureon) and DPP-4 inhibitors such as Januvia (sitagliptin) and Onglyza (saxagliptin). The latest class of medications for diabetes is SGLT2 inhibitors, including Invokana (canagliflozin), Farxiga (dapagliflozin), and Jardiance (empagliflozin). Combination drugs containing medications from more than one class — such as Actoplus Met, Glucovance, and Janumet — are also available. There are now 11 categories of drugs approved for controlling blood glucose levels, and more are in development.
Approximately 34 million people in the U.S., or almost 1 in 10 people, have type 2 diabetes. Not everyone with diabetes has been diagnosed; it is estimated that one-third of those with diabetes may not realize they have it. Early warning signs such as fatigue or increased thirst and urination are often dismissed as signs of aging or symptoms of other conditions. Type 2 diabetes is most commonly diagnosed in adults age 45 or older but may also occur in younger adults and children.
In 2017, diabetes was the seventh most common cause of death for Americans. Diabetes — which raises the risk for heart disease and kidney disease — is also very commonly listed as an underlying or contributing factor on death certificates. According to one study, type 2 diabetes can shorten life expectancy by as much as 10 years.
People with type 2 diabetes have better outcomes and fewer complications when they follow diet guidelines, exercise, and use medications and insulin as directed. Type 2 diabetes can’t be cured, but some people are able to reverse diabetes, or go into remission, by losing significant weight, exercising, and changing their diets. Doctors consider diabetes reversed when a person is able to control blood glucose without medication over a long period of time. Reversal is more likely in early stages of diabetes.