Type 2 diabetes mellitus is a chronic condition in which your body loses its ability to use insulin effectively, leading to persistently high blood sugar. It accounts for the vast majority of diabetes cases, and recent CDC data shows that 15.8% of U.S. adults now have some form of diabetes, with 4.5% undiagnosed. The condition develops gradually, often over years, and can cause serious damage to blood vessels, nerves, and organs when blood sugar stays elevated for long periods.
How Type 2 Diabetes Develops
Insulin is the hormone that moves sugar (glucose) from your bloodstream into your cells for energy. In type 2 diabetes, two things go wrong. First, your cells stop responding normally to insulin, a problem called insulin resistance. Second, the insulin-producing cells in your pancreas gradually wear out and can no longer keep up with demand.
Insulin resistance typically comes first. Your liver, muscles, and fat tissue all become less responsive to insulin’s signal. When the liver resists insulin, it keeps releasing glucose into the blood even when levels are already high. Fat tissue, particularly in people with excess weight, releases inflammatory signals that worsen the problem. Immune cells infiltrate fat tissue and trigger a chronic, low-grade inflammatory response that spreads insulin resistance throughout the body. A high-fat diet can even induce insulin resistance in the brain, which further increases the liver’s glucose output and drives overeating.
For a while, your pancreas compensates by pumping out more insulin. But this overwork eventually leads to failure. The insulin-producing beta cells either can’t expand enough in number or lose their ability to sense glucose properly. Once beta cell output drops below what’s needed to overcome the resistance, blood sugar rises and stays elevated. That’s the point at which type 2 diabetes begins.
Who Is at Risk
The strongest risk factors, according to the CDC, are carrying excess weight, being 45 or older, and having a parent or sibling with type 2 diabetes. Being physically active fewer than three times a week also raises your risk, as does having non-alcoholic fatty liver disease or a history of gestational diabetes.
Certain racial and ethnic groups face higher risk, including African American, Hispanic or Latino, American Indian, Alaska Native, some Pacific Islander, and some Asian American populations. If you already have prediabetes (blood sugar above normal but not yet in the diabetes range), that’s an added risk factor on its own.
Symptoms to Recognize
Type 2 diabetes often develops silently. Many people have no obvious symptoms for years, which is why nearly a third of cases go undiagnosed. When symptoms do appear, they stem from excess glucose circulating in the blood.
The three classic signs are frequent urination (your kidneys work overtime to filter out excess sugar), increased thirst (to replace the fluids lost through urination), and increased hunger (because your cells aren’t getting the glucose they need for fuel). Beyond those, common indicators include extreme fatigue, blurry vision, slow-healing cuts or bruises, unexplained weight loss, and tingling, pain, or numbness in the hands and feet.
How It Is Diagnosed
Diagnosis relies on blood tests that measure how much glucose is in your blood. The American Diabetes Association’s 2025 standards define three ranges:
- Normal: Fasting blood sugar below 100 mg/dL, or an A1C below 5.7%.
- Prediabetes: Fasting blood sugar of 100 to 125 mg/dL, or an A1C of 5.7% to 6.4%.
- Diabetes: Fasting blood sugar of 126 mg/dL or higher, or an A1C of 6.5% or higher.
The A1C test reflects your average blood sugar over the past two to three months, so it gives a broader picture than a single fasting reading. If you don’t have obvious symptoms of high blood sugar, diagnosis requires two abnormal test results, either from different tests taken at the same time or the same test repeated on a separate day.
The U.S. Preventive Services Task Force recommends screening for adults aged 35 to 70 who have a BMI of 25 or higher. If your initial results come back normal, rescreening every three years is a reasonable approach.
Long-Term Complications
Sustained high blood sugar damages small and large blood vessels throughout the body. The complications tend to accumulate over time, but people with type 2 diabetes may already have some damage at diagnosis because the disease often goes undetected for years.
Eye disease (retinopathy) is one of the most common concerns. Around 12% of U.S. adults with diabetes have some level of vision impairment. Because retinopathy can be present at the time of a type 2 diagnosis, a comprehensive dilated eye exam is recommended right away rather than waiting.
Nerve damage (neuropathy) affects a large proportion of people with diabetes. Up to half of those with diabetic nerve damage don’t have obvious symptoms, which is why screening starts at diagnosis. When it does cause symptoms, it typically shows up as numbness, tingling, or pain in the feet. Nerve damage is a component cause in 78% of diabetic foot ulcers, making regular foot checks essential.
The cardiovascular risks are equally serious. Type 2 diabetes significantly raises the likelihood of heart attack, stroke, and kidney disease. These macrovascular complications are a leading cause of death in people with the condition.
Treatment Approaches
Treatment starts with lifestyle changes. Increasing physical activity, losing weight, and adjusting your diet can meaningfully lower blood sugar and, in some cases, put the disease into remission. Most people also need medication.
Metformin has long been the standard first medication. It works by reducing the amount of glucose your liver releases and helping your cells take up glucose more effectively. It’s inexpensive, well-studied, and has a strong safety profile. When metformin alone isn’t enough to bring blood sugar to target, a second medication is added. The choice depends on factors like whether you have heart or kidney disease, your weight goals, and cost.
Two newer classes of medication have changed the treatment landscape. One class helps the kidneys flush excess glucose out through urine, which also lowers blood pressure and protects the kidneys. The other mimics a gut hormone that boosts insulin release after meals, slows digestion, and reduces appetite, often leading to significant weight loss. For people with established heart disease or high cardiovascular risk, European guidelines now recommend starting with one of these newer medications rather than metformin.
Can Type 2 Diabetes Be Reversed?
Remission is possible, and it has a formal definition: an A1C below 6.5% maintained for at least three months without any glucose-lowering medication. The key driver of remission is substantial weight loss.
The results from major clinical trials are striking. In the DiRECT study, participants who lost roughly 10% of their body weight saw a 46% remission rate at one year, compared to just 4% in the control group. The DIADEM-I trial achieved a 61% remission rate at one year with an intensive lifestyle program. These are real, measurable reversals of the disease, not just improvements.
Remission is more likely when diabetes is caught early, before years of high blood sugar have exhausted the insulin-producing cells. In the Look AHEAD trial, which followed participants longer, remission rates dropped from 11.5% at one year to 7.3% at four years, illustrating that sustaining weight loss is the hard part. Remission also doesn’t mean the disease is gone permanently. Blood sugar monitoring continues, and the condition can return if weight is regained.