Diabetes

What is diabetes?

Diabetes (known formally as diabetes mellitus) is a chronic illness affecting more than 37 million Americans — about one out of every 10 people. Its primary feature is high blood sugar levels, also called blood glucose levels. But what is glucose, and how is having too much of it in your bloodstream harmful?

When you digest your food, chemical processes take place in your body that break down food, primarily carbohydrates, into sugars, or glucose. Glucose is an important fuel for cells throughout your body. But those cells can’t get access to this critical fuel source without a substance, produced naturally by your pancreas, called insulin.

In someone without diabetes, an increase in blood sugar, usually after a meal, causes the pancreas to release insulin into the bloodstream so that glucose can move into the body’s cells and be used as fuel. Once the sugar is in the cells and no longer in the bloodstream, the person has normal glucose levels.

But with diabetes, that process stops working, either because the pancreas fails to produce sufficient insulin, or because the body’s cells become resistant to insulin (or both). As a result, the glucose, unable to enter the cells, lingers in the bloodstream, circulating throughout the body and causing damage to blood vessels, nerves, and organs.

How is diabetes diagnosed? Normally, adults have their blood-sugar levels monitored as part of their regular wellness checkups. Several tests may be used to diagnose diabetes, including those that assess sugar levels while fasting, after having consumed sugar, at random times, or as an average over recent months. If a person does not have normal blood sugar levels — especially if they’re experiencing symptoms — they will likely be diagnosed with diabetes or prediabetes.

However, sometimes diabetes is not detected until someone shows high blood sugar symptoms. The two most common symptoms are excessive urination and increased thirst. If left untreated, other symptoms can include unexplained weight loss, fatigue, and blurry vision.

What is prediabetes?

Just as the name implies, prediabetes is a condition that’s often (though not always) a precursor to full-blown diabetes. If you’re diagnosed with prediabetes, that’s a warning sign to manage your blood sugar levels through lifestyle changes and possibly medication, to prevent it from developing into diabetes.

How is prediabetes diagnosed? Doctors use the same tests for prediabetes as they do for diabetes. Most tests measure the amount of glucose in the blood, expressed as micrograms per deciliter, or mg/dL. A reading above the normal range but not yet in the range of diabetes results in a prediabetes diagnosis. For example, on a fasting glucose test, a normal level would be below 100 mc/dL, prediabetes would be diagnosed for someone in the range of 100 to 125 mc/dL, and someone with a result higher than 125 mc/dL would receive a diabetes diagnosis.

Another test to diagnose prediabetes is a blood test that measures hemoglobin A1c (HbA1c). This test can be done any time during the day and does not require fasting. It reflects your average blood sugar level over the past three months. A normal reading is below 5.7%. A reading of 5.7% to 6.4% means prediabetes, and people with diabetes have readings of 6.5% or higher.

About one in 10 people diagnosed with prediabetes will go on to develop type 2 diabetes in the next 12 months. The lifetime risk of this happening is about 70%. Fortunately, however, a prediabetes diagnosis does not mean you’re destined to develop diabetes.

It’s possible not only to avoid developing diabetes, but also to reverse prediabetes. The key is to overcome insulin resistance, which is linked to body fat, especially around the belly. Therefore, regular exercise — at least 30 minutes each day — and eating healthy foods are crucial.

While there is no one prescribed “prediabetes diet,” there are certain guidelines you should follow to help avoid disease progression. For example, eating too many carbohydrates — especially refined and processed carbohydrates and sugary beverages — will cause your blood sugar to spike. Vegetables, beans, and whole grains are good forms of carbohydrates. Eating too many calories causes your body to store the extra energy as fat, and fat can interfere with the communication systems between insulin and body cells, which worsens insulin resistance. Other guidelines include getting protein from lean meats, poultry, fish, and legumes and drinking plenty of water.

What are the symptoms of diabetes?

Diabetes symptoms don’t always appear until the disease has progressed, which is why it’s important to have a periodic wellness visit with your primary care clinician that includes lab work. The earlier the disease is detected, the better you’ll be able to manage it.

One of the key diabetes signs is a cluster of symptoms that include excessive thirst and urination. This happens because the kidneys release the extra glucose into the urine, and in order to do that, they must also release large amounts of water. Expelling so much fluid makes you dehydrated, which is why you become so thirsty.

Sometimes, because cells are deprived of glucose, they turn to another fuel source called ketones, which are produced by the liver. Ketones are acidic, and an accumulation of them in the bloodstream can lead to a dangerous condition called ketoacidosis.

Long-term, diabetes can cause several serious health problems. Excessive blood sugar damages blood vessels in the eyes, causing a condition called retinopathy, which can lead to blindness if left untreated. High blood glucose also damages nerves, often in the feet, legs, and hands. People with diabetes sometimes develop sores on their feet that they cannot feel because of nerve damage. When those sores go untreated, they can become deep skin ulcers that can take months to heal. Persistent high blood sugar levels can damage blood vessels, raise blood pressure, and tax the kidneys, leading to an increased risk for heart disease and kidney disease.

What's the difference between type 1 diabetes and type 2 diabetes?

Both type 1 diabetes and type 2 diabetes share the key connection between blood sugar and insulin. And the same criteria are used to diagnose both types. But the reasons why each happens differs.

During digestion, food is broken down into basic components. Carbohydrates are broken down into simple sugars, primarily glucose. Glucose is a critically important source of energy for the body's cells. To provide energy to the cells, glucose needs to leave the blood and get inside the cells.

The hormone insulin, produced by the pancreas and released into the bloodstream, signals the body’s cells to take up glucose. The pancreas produces insulin continuously to balance blood sugar levels. After a meal, when levels of glucose in the blood rise, the pancreas normally produces more insulin.

Type 1 diabetes occurs when some or all of the insulin-producing cells in the pancreas are destroyed. Without insulin, glucose accumulates in the bloodstream rather than entering the cells. As a result, the body cannot use this glucose for energy. In addition, the high levels of glucose that remain in the blood cause excessive urination and dehydration, and damage body tissues.

Type 1 diabetes is an autoimmune disease. This means it begins when the body's immune system attacks cells in the body. In type 1 diabetes, the immune system destroys insulin-producing cells (beta cells) in the pancreas.

Type 2 diabetes occurs when your body's cells resist the normal effect of insulin, which is to drive glucose from the bloodstream into cells. This condition is called insulin resistance. As a result, glucose builds up in the blood.

In people with insulin resistance, the pancreas responds to higher blood glucose levels by making extra insulin in an attempt to maintain a normal blood sugar level. Over time, the body's insulin resistance worsens. In response, the pancreas makes more and more insulin. At some point, the insulin-producing beta cells can become less functional due to the stress of constant insulin production. The pancreas may produce less insulin and some beta cells may stop working altogether.

Can diabetes be prevented?

Type 1 diabetes cannot be prevented. But you can prevent type 2 diabetes even if it runs in your family.

If a close relative — particularly, a parent or sibling — has type 2 diabetes, or if your blood glucose test shows prediabetes (defined as blood glucose levels between 100 and 125 mg/dL), you are at increased risk for developing type 2 diabetes. You can help to prevent type 2 diabetes by:

• maintaining your ideal body weight
• exercising regularly — such as a brisk walk of one to two miles in 30 minutes — at least five times a week, even if that does not result in you achieving an ideal weight. That’s because regular exercise reduces insulin resistance even if you don’t lose weight.
• eating a healthy diet
• taking medication. The medication metformin (Glucophage) offers some additional protection for people with pre-diabetes.

If you already have type 2 diabetes, you can still delay or prevent complications by doing the following.

Keep control of your blood sugar. This helps reduce the risk of most complications.

Lower your risk of heart-related complications. Aggressively manage other risk factors for atherosclerosis, such as:

• high blood pressure
• high cholesterol and triglycerides
• cigarette smoking
• obesity.

Visit an eye doctor and a get a foot exam every year. This can help you reduce the risk of eye and foot complications.

Diabetes treatment

The goal of diabetes treatment is to keep blood sugar levels within a target range. A common HbA1c goal is below 7%, though your goal may be customized for your specific situation.

Treating type 2 diabetes

Diet and exercise

In most cases, type 2 diabetes treatment begins with weight reduction through diet and exercise. For some people, type 2 diabetes can be controlled just with aggressive weight loss and exercise. Even if medications are required, diet and exercise remain important for controlling diabetes.

Medications

Metformin. Oral metformin remains the first go-to drug in the treatment of type 2 diabetes. The most common side effects are abdominal discomfort and irregular bowel habits.

According to 2025 guidelines from the American Diabetes Association (ADA), doctors should consider adding either a GLP-1 receptor agonist or SGLT-2 inhibitor if blood sugar levels are still too high despite metformin or if a person has an increased risk of cardiovascular or kidney disease.

Glucagon-like peptide 1 (GLP-1) receptor agonists. These drugs mimic the effects of a substance the gut produces naturally to help regulate blood sugar. GLP-1 receptor agonists also slow down digestion, which can help with weight loss but can also produce unpleasant symptoms, including nausea, vomiting, and diarrhea. Examples include liraglutide (Victoza), semaglutide (Ozempic) and dulaglutide (Trulicity).

Sodium-glucose co-transporter 2 (SGLT-2) inhibitors. These drugs work by blocking the kidney's ability to reabsorb sugar. Examples include empagliflozin (Jardiance), canagliflozin (Invokana), and dapagliflozin (Farxiga). SGLT-2 inhibitors increase the risk of vaginal yeast infections as well as urinary tract infections.

GLP-1 receptor agonists and SGLT-2 inhibitors have additional health benefits beyond helping with blood sugar control. These include:

Supporting weight loss. Both can help a person with diabetes shed pounds. GLP-1 receptor agonists are more effective for weight reduction compared with the SGLT-2 inhibitors.

Reducing cardiovascular disease risk. Drugs from both classes lower the risk of heart attack and stroke in people with diabetes. For people with heart failure and diabetes, SGLT-2 inhibitors have been shown to decrease hospitalizations and improve survival.

Slowing progression of chronic kidney disease. SGLT-2 inhibitors can slow down the progression of diabetic kidney disease and may help prevent kidney failure related to other conditions.

Insulin

Type 2 diabetes develops when the pancreas cannot make enough insulin to overcome insulin resistance. In advanced type 2 diabetes, or for people who want to tightly control glucose levels, insulin may be needed.

Treatment plans that include both very long-acting insulin and very short-acting insulin are frequently the most successful for controlling blood sugar. Very short-acting insulin is used with meals, to help control the spike in blood sugar levels that occurs with a meal. If a person does not eat on a regular schedule, very short-acting insulin can be particularly helpful.

The most worrisome side effect of insulin is low blood sugar (hypoglycemia). The usual symptoms are sudden weakness, sweating, feeling unwell, and not thinking clearly.

Other medicines

In addition to medicines that help control the level of blood sugar, people with type 2 diabetes often take other medicines that reduce the risk or slow the onset of the complications of diabetes. These include medications that:

• slow the worsening of kidney disease
• lower cholesterol
• lower blood pressure
• protect against heart attacks.

Treating type 1 diabetes

Treatment of type 1 diabetes requires daily insulin injections. The injected insulin makes up for the insulin that is not produced by the body.

People with type 1 diabetes must properly regulate both their dietary intake and their dose of insulin. There are multiple types of insulin: some are meant to be given at every meal, while longer-acting types can be given less frequently. Most people with type 1 diabetes need two to four injections per day.

If a person takes too much insulin relative to their dietary intake, or if they forget to eat, they can develop dangerous hypoglycemia. If they take too little insulin, or eat too much, they can develop ketoacidosis. In order to keep blood sugar levels at a normal and relatively constant level, a person with type 1 diabetes typically is advised to eat, exercise, and take insulin at about the same times every day. Regular habits help to keep glucose levels within the normal range.

An increasing number of people with type 1 diabetes use insulin pumps. Insulin pumps deliver a regulated dose of insulin through a needle implanted under the skin. The insulin pump is worn in a pack on the body. Some pumps include a sensor that constantly measures the level of blood sugar and adjusts the dose of insulin accordingly. Compared with individual injections, insulin pumps provide better blood sugar control over time and also reduce risk of hypoglycemia.

Regular medical care is important for people with type 1 diabetes in order to detect, treat, and monitor complications of the disease (including diseases of the eye, kidney, heart, and nerves).

Blood sugar monitoring

Blood sugar monitoring is an important part of treatment in people with diabetes. Checking blood sugar can be done with test strips or a blood-glucose monitor. This type of testing is usually done first thing in the morning, before and after meals, and before bedtime.

A continuous glucose monitor (CGM) measures blood sugar every few minutes using a sensor inserted under the skin. A CGM is usually placed on the back of the upper arm or somewhere on the abdomen. Initially developed for people with type 1 diabetes, CGMs have become more common in people with type 2 diabetes and prediabetes, as well as athletes and fitness enthusiasts. These trackers provide real-time blood sugar information through smartphone apps.