Type 2 diabetes mellitus is a chronic condition in which your body loses its ability to use insulin effectively, causing blood sugar levels to rise and stay elevated. It accounts for roughly 90% to 95% of all diabetes cases. CDC data from 2021 to 2023 show that about 15.8% of U.S. adults have diabetes, and nearly a third of those cases (4.5% of the adult population) are undiagnosed.
How Type 2 Diabetes Develops
Insulin is a hormone that moves sugar from your bloodstream into your cells, where it’s used for energy. In type 2 diabetes, your cells gradually stop responding to insulin the way they should. This is called insulin resistance. Your pancreas compensates by making more insulin, but over time it can’t keep up with the demand. The result is a buildup of sugar in the blood that, left unchecked, damages tissues throughout the body.
This is different from type 1 diabetes, where the immune system attacks and destroys the insulin-producing cells in the pancreas. In type 2, the pancreas still makes insulin. The problem is that the body’s cells don’t use it well, and eventually the pancreas produces less of it.
Common Symptoms
Type 2 diabetes often develops so slowly that many people have it for years without knowing. When symptoms do appear, they typically include increased thirst, frequent urination, persistent hunger, unexplained weight loss, and fatigue. High blood sugar forces the kidneys to work overtime filtering excess glucose, pulling extra water from your tissues in the process. That’s why you urinate more and feel thirstier.
Other signs can be subtler: blurred vision, slow-healing cuts or sores, frequent infections, and numbness or tingling in the hands and feet. Some people develop patches of darkened skin, most often in the armpits and along the neck. Because these symptoms can seem minor or unrelated, many cases are caught only through routine blood work.
Risk Factors
Some risk factors are within your control and some aren’t. The CDC lists the following as key factors for both prediabetes and type 2 diabetes:
- Weight. Having overweight or obesity is the single strongest modifiable risk factor.
- Physical inactivity. Exercising fewer than three times a week raises your risk.
- Age. Risk increases at age 45 and older, though younger adults are increasingly diagnosed.
- Family history. A parent or sibling with type 2 diabetes significantly increases your likelihood.
- Ethnicity. African American, Hispanic or Latino, American Indian, Alaska Native, some Pacific Islander, and some Asian American populations face higher risk.
- Gestational diabetes. Having had diabetes during pregnancy, or delivering a baby weighing over 9 pounds, raises long-term risk.
- Non-alcoholic fatty liver disease. Fat buildup in the liver is closely linked to insulin resistance.
Genetics loads the gun, but lifestyle pulls the trigger. Having a family history doesn’t guarantee you’ll develop the condition, and many people with no family history develop it due to weight, inactivity, or other metabolic factors.
How It’s Diagnosed
Three main blood tests are used, and any one of them can confirm a diagnosis when the result falls above a specific threshold.
The A1C test measures your average blood sugar over the past two to three months. A result below 5.7% is normal, 5.7% to 6.4% indicates prediabetes, and 6.5% or higher means diabetes. This test doesn’t require fasting, which makes it convenient.
The fasting plasma glucose test measures blood sugar after you haven’t eaten for at least eight hours. Normal is below 100 mg/dL, prediabetes falls between 100 and 125 mg/dL, and 126 mg/dL or higher indicates diabetes.
The oral glucose tolerance test measures blood sugar two hours after you drink a sugary liquid. Normal is below 140 mg/dL, prediabetes is 140 to 199 mg/dL, and 200 mg/dL or higher confirms diabetes. Doctors typically repeat an abnormal result on a second occasion before making a formal diagnosis.
Long-Term Complications
Persistently high blood sugar damages blood vessels, and complications are grouped by whether they affect small vessels or large ones. Small-vessel damage (microvascular complications) hits three areas hardest: the eyes, the kidneys, and the nerves. Damage to blood vessels in the retina can progress from mild changes to vision-threatening disease requiring laser treatment. Kidney damage shows up as protein leaking into the urine and, in advanced stages, can lead to kidney failure. Nerve damage often starts in the feet, causing tingling, numbness, and eventually foot ulcers that heal poorly, sometimes requiring amputation.
Large-vessel damage (macrovascular complications) increases the risk of heart attack, stroke, and poor circulation in the legs. These aren’t separate problems. Small-vessel damage and large-vessel damage feed into each other, meaning that someone with early kidney disease or nerve damage is also at higher risk for heart disease. This interconnection is why managing blood sugar, blood pressure, and cholesterol together matters so much.
Treatment Approaches
Lifestyle changes are the foundation. Losing weight, eating fewer refined carbohydrates, and exercising regularly all improve insulin sensitivity directly. For many people with early or mild type 2 diabetes, these changes alone can bring blood sugar into a healthy range.
When medication is needed, metformin has historically been the standard first-line treatment. It works primarily by reducing the amount of sugar your liver releases into the bloodstream and by helping your cells respond better to insulin.
Newer drug classes have changed the treatment landscape significantly. One class helps the kidneys flush excess sugar out through the urine, which also benefits blood pressure, kidney function, and heart health. Another class mimics a gut hormone that triggers insulin release after meals, slows digestion, and reduces appetite, often producing meaningful weight loss. Current American Diabetes Association guidelines recommend these newer medications not just for blood sugar control but specifically for people who have or are at high risk for heart disease, heart failure, or chronic kidney disease, regardless of their A1C level. When additional blood sugar lowering is needed, these medications are now preferred over insulin in most situations because they carry a lower risk of dangerous blood sugar drops and tend to help with weight rather than contributing to weight gain. Adding one of these therapies to metformin typically lowers A1C by 1% to over 2%.
Insulin remains an important tool for people whose blood sugar is very high at diagnosis or whose condition progresses to the point where other medications aren’t enough.
Remission Through Weight Loss
Type 2 diabetes was long considered a one-way street, but research has shown that remission is possible. Remission is defined as achieving a normal A1C (below 6.5%) on two occasions at least six months apart, with no diabetes medications of any kind. The key driver is weight loss. Losing roughly 33 pounds (about 15 kg) can restore normal function to the processes that cause type 2 diabetes in many people. This works because excess fat, particularly around the liver and pancreas, drives insulin resistance and impairs insulin production. Removing that fat can reverse both problems.
Remission is most achievable for people diagnosed relatively recently, before the insulin-producing cells in the pancreas have been exhausted. The longer someone has had diabetes, the harder remission becomes, though it’s not impossible. Sustained weight loss is critical: regaining the weight typically brings the diabetes back.