Diabetes is a chronic disease characterized by high blood sugar, or glucose. 

This glucose, which is derived from the food we eat, is a critical source of energy for the body’s cells. Once glucose enters the blood, the pancreas releases the hormone insulin, which shepherds the glucose from the blood into cells, feeding them their essential fuel. 

However, in people with diabetes, the body doesn’t make enough insulin or doesn’t use the insulin as it should. As a result, their blood sugar remains elevated. Over time, these high blood sugar levels can lead to serious complications, including heart disease, kidney disease and blindness, according to the Mayo Clinic.

About 11.3% of the U.S. population, or 37.3 million people, has diabetes, according to a recent report from the Centers for Disease Control and Prevention (CDC); about 8.5 million, or 23%, of those people have undiagnosed diabetes. In addition, about 96 million people in the U.S. have prediabetes, a condition in which blood sugar levels are high but not high enough to be diagnosed as diabetes, but most are unaware of it.

Types of diabetes

There are three broad categories of diabetes, according to the Mayo Clinic: type 1 diabetes, type 2 diabetes and gestational diabetes.

Type 1 diabetes is an autoimmune disease, because the person’s own immune system mistakenly attacks the insulin-producing cells (called beta cells) in the pancreas. This stops the secretion of insulin, thus allowing sugar to build up in the bloodstream. 

Type 2 diabetes occurs when the body’s cells do not respond to insulin the way they should. At first, the pancreas makes up for the shortfall by secreting more insulin, but eventually, it cannot keep up, causing sugar to build up in the bloodstream.

Gestational diabetes happens when someone who did not previously have diabetes develops diabetes during pregnancy. During pregnancy, the hormones produced to sustain the pregnancy, such as estrogen and cortisol, make the pregnant person’s own cells more resistant to insulin, according to Johns Hopkins Medicine. Normally, the pancreas produces more insulin to compensate, but sometimes, it can’t keep up, allowing glucose to build up in the bloodstream. Sometimes, gestational diabetes resolves after pregnancy; other times, the condition becomes chronic.

Prevention & risk factors

Although type 1 and type 2 diabetes have different causes, they share two key risk factors: the person inherits a predisposition to the disease, and then something in their environment triggers it, according to the American Diabetes Association (ADA).

In most cases of type 1 diabetes, people inherit genetic risk factors from both parents — it is believed these factors are more common in white people, because they have the highest rate of this form of diabetes, says the ADA.   

Environmental triggers, according to the ADA, can include cold weather (type 1 diabetes develops is more common in cold climates) and certain viral infections (enteroviruses are considered the strongest candidates), according to the National Library of Medicine. Diet and lifestyle habits don’t cause type 1 diabetes, adds the CDC. 

At the moment, there is no known way to prevent type 1 diabetes, but researchers are working on research to do just that, as well as limit the destruction of insulin producing cells in the pancreas of newly diagnosed patients, according to a 2020 paper published in the journal Frontiers in Endocrinology.

Genetics plays a role in type 2 diabetes, so someone who has a family history of the disease is more likely than others to develop it, according to the National Institutes of Health. Other factors that increase a person’s chances of developing this type of diabetes include: being 45 years or older, being overweight or obese, having other health conditions such as high blood pressure, along with other risk factors, the NIH says. A person who is African American, American Indian, Asian American, Pacific Islander or Hispanic American, has an increased risk of developing type 2 diabetes, according to the CDC.

Lifestyle changes can lower a person’s risk of developing type 2 diabetes and are especially important for people who have prediabetes, according to the CDC. Data shows that even moderate weight loss and exercise can prevent or delay type 2 diabetes in people at high risk of developing the condition, according to this 2010 paper published in the journal Diabetes Care.

People who had gestational diabetes are also at increased risk of developing type 2 diabetes later in life. High blood pressure and/or abnormal cholesterol and triglyceride levels are other risk factors for type 2 diabetes.

Symptoms & complications

Symptoms of high blood sugar include frequent urination, persistent thirst and hunger, sores that take long to heal, blurry vision, loss of weight without trying and tingling extremities, the CDC says. 

Type 1 diabetes typically starts in childhood or as a young adult, but it can occur at any age. It may also include symptoms such as nausea, heaving or stomach pains. 

Type 2 diabetes typically starts in adulthood, but more and more people are developing it at a young age.  Symptoms of high blood sugar usually emerge slowly, so they aren’t always easy to spot. Therefore, it is important to pay attention to factors that raise the risk of diabetes. 

There has been a surge in cases of both type 1 and type 2 diabetes among youth, a recent CDC report says. Between 2001 and 2017, the number of people under age 20 living with type 1 diabetes increased by 45%, and the number living with type 2 diabetes grew by 95%, the agency said. 

Gestational diabetes usually doesn’t have any symptoms, but doctors often test for it between the 24th and 28th week of pregnancy.  

If diabetes is left uncontrolled, it can lead to serious — and sometimes life-threatening — complications. The longer the disease is untreated, the higher the risk of these complications, according to the Mayo Clinic.

Diabetes dramatically raises the likelihood of heart disease and other cardiovascular events, including heart attacks and strokes, according to a review of existing research published in 2015 in the World Journal of Diabetes. It all stems back to persistent high sugar levels, which over time can damage the arteries that carry blood, oxygen and nutrients around the body, says the British Heart Foundation. Once the arteries are damaged, it’s easier for fat to clog up arterial walls and limit blood flow. If the arteries carrying blood to the heart are obstructed, it can lead to a heart attack — if the arteries carrying blood to the brain get congested, that can culminate in stroke.

Nerve damage is also a common complication , as excess sugar can impair the walls of the tiny blood vessels that nourish the nerves, eventually leading to a condition called neuropathy, or a loss of all sense of feeling in the affected limbs that affects more than 90% of people living with diabetes, according to a 2015 study published in the World Journal of Diabetes. That nerve trauma may also make people more vulnerable to infections and lead sores and cuts to heal more slowly. In particular, people with diabetes are susceptible to problems in their legs and feet, which can result in amputation if left untreated, says the Mayo Clinic.

Diabetes can also damage the kidneys, which contain millions of blood vessel clusters that filter waste in blood. If left unaddressed, a person with kidney damage resulting from diabetes may need dialysis, or even a kidney transplant. Research suggests that diabetes has become the single most frequent cause of end-stage kidney disease, according to a 2019 paper published in the journal Molecular Metabolism.  Uncontrolled blood sugar can also weaken the blood vessels of the eye (diabetic retinopathy) to the point of causing blindness, says the Mayo Clinic.

A common but severe complication of type 1 diabetes (and, less commonly, type 2 diabetes) is diabetic ketoacidosis, which occurs when there is a drastically low level of insulin in the body, according to the National Library of Medicine. This means the body can’t use sugar for energy, so it starts to use fat instead. As a result, compounds called ketones are released, causing the blood to become acidic and, in turn, toxic. Diabetic ketoacidosis is sometimes the first sign of type 1 diabetes in people who haven’t been diagnosed; if left untreated, it can be deadly.

Diagnosis

The American Diabetes Association recommends screening for type 2 diabetes for all adults age 45 and older, as well as for: Individuals who are overweight or have obesity, plus have one or more diabetes risk factors; women who have  had gestational diabetes; people with prediabetes; kids who are overweight or have obesity, and have a family history of type 2 diabetes or one or more other risk factors, according to the Mayo Clinic. 

Normal blood sugar levels vary from person to person, but a normal range for fasting blood sugar (the amount of glucose in your blood at least eight hours after a meal) is between 70 and 100 milligrams per deciliter (mg/DL), according to the World Health Organization (WHO). According to the ADA, the normal blood sugar range two hours after someone eats is generally less than 140 mg/DL, according to the ADA.

There are several ways for doctors to diagnose diabetes, according to the ADA (but each test typically needs to be repeated on a second day to diagnose diabetes):

• One method is the A1C blood test, which measures average blood glucose over the preceding three months. The test measures glucose attached to hemoglobin, the oxygen-carrying protein in blood. The red blood cells that carry this protein live for about three months, so measuring them at a single time point provides a snapshot of the general level of glucose in the blood. An A1C result of less than 5.7% is considered normal,  between 5.7% and 6.4% suggests prediabetes, and 6.5% or greater indicates diabetes.
• Another test, the fasting plasma glucose test, reveals how effectively the body metabolizes glucose and requires the patient to fast for eight hours before taking the test. More than 126 mg/DL of glucose in the blood signals diabetes.
• The oral glucose tolerance test, which is often used to detect gestational diabetes, requires the patient to consume a very sugary drink. Two hours later, the person undergoes a blood test. A repeated result of 200 mg/DL or greater of glucose in the blood would mean a diabetes diagnosis.
• Given that a family history of diabetes raises the risk of developing the condition, people who fall into that category should talk to their doctor about being screened.

Treatment

People with diabetes are usually asked to regularly monitor their blood sugar levels in order to keep an eye on the impact of medication, diet and exercise on their glucose levels, says the Mayo Clinic. Keeping track of these levels can be done by either using a device called a continuous glucose monitor (CGM), which measures blood sugar every few minutes using a sensor inserted under the skin, or with the help of a portable electronic device called a blood sugar meter using a small drop of blood.

The treatment for type 1 diabetes is regular insulin injections, sometimes delivered with an insulin pump, a catheter device that automatically dispenses the hormone, alongside attention to diet and exercise to prevent complications. 

The first step in managing type 2 diabetes is to lose weight by eating healthy — including smaller portion sizes; increased intake of high-fiber foods such as fruits, non-starchy vegetables and whole grains; and fewer calories — and getting regular exercise, says the Mayo Clinic.

Doctors also may prescribe insulin, other injectable medications or oral diabetes medicines, such as metformin, to address the high blood sugar. Patients are typically given blood sugar targets and are advised to check their glucose levels periodically.  

ADA guidelines indicate that weight loss surgery, also called bariatric surgery, is an option for individuals with inadequately controlled type 2 diabetes and a BMI of 35 or greater, according to Penn Medicine Lancaster General Health.

In 2016, the FDA approved the use of an “artificial pancreas” that automatically tests blood glucose levels periodically and releases insulin accordingly, Live Science previously reported. The product relies on a coin-size transmitter attached to a tiny needle that is inserted into the skin to continuously track glucose levels, a pump that delivers precise doses of insulin as needed through a separate catheter, and a computer chip that uses data from both components to optimize the delivery of insulin on a minute-by-minute basis.

Is diabetes curable?

Although research is ongoing, type 1 diabetes has no cure, says the Mayo Clinic. For example, researchers have found a way to convert human stem cells into insulin producing cells that at least in mice have shown to control blood sugar levels, according to a 2020 study published in the journal Nature Biotechnology.  

There is no cure for type 2 diabetes either, but with substantial and sustained weight loss, patients can go into remission, which means their blood sugar levels fall into the normal range again, according to the NIH. However, this doesn’t mean the person has been “cured” or completely rid of diabetes for good, because blood glucose levels tend to fluctuate with weight, so if the person regains the weight, their blood sugar levels could elevate to a diabetic range back again.   

Some studies have shown that bariatric surgery can help some diabetes patients achieve remission.  For instance, in a UK study involving about 2500 patients with type 2 diabetes, researchers found an 18-fold increased chance of diabetes remission after bariatric surgery in comparison with patients not undergoing surgery, according to a 2015 study published in the journal JAMA Surgery.

Another study, published in the journal The Lancet Diabetes & Endocrinology in 2019, showed that more than a third (36%) of people with type 2 diabetes who took part in a weight management program were in remission two years later.

This article is for informational purposes only and is not meant to offer medical advice.

This article was updated on Apr. 14, 2022, by Live Science contributor Natalie Grover, with additional reporting by Stephanie Pappas, Live Science Contributor.

Additional resources

• Check out this primer on eating well to manage diabetes in this eating plan from the ADA.
• Learn more about preventing diabetes in this explainer focused on prediabetes, from the Cleveland Clinic.
• Get a deeper look into the science behind diabetes, and the impact of the disease on American society in this book “Cheating Destiny: Living With Diabetes, America’s Biggest Epidemic,” by James Hirsch.

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