Type 2 diabetes is a condition where your body can’t use insulin effectively enough to keep blood sugar at healthy levels. It accounts for roughly 90–95% of all diabetes cases and currently affects about 589 million adults worldwide, a number projected to reach 853 million by 2050. Unlike type 1 diabetes, where the immune system destroys insulin-producing cells, type 2 develops gradually as your cells become increasingly resistant to insulin’s signal, and your pancreas eventually can’t produce enough to compensate.
How Type 2 Diabetes Develops
Insulin is a hormone that acts like a key, unlocking your cells so they can absorb sugar from the bloodstream and use it for energy. In the early stages of type 2 diabetes, your cells stop responding normally to that key. Your pancreas compensates by producing more insulin, but over time it can’t keep up with the demand. Sugar builds up in your blood instead of entering cells, and both the elevated blood sugar and the excess insulin cause damage throughout the body.
This process doesn’t happen overnight. Most people pass through a stage called prediabetes, where blood sugar is elevated but not yet high enough for a diabetes diagnosis. That window can last years, and it’s the most important period for intervention.
Genetics and Lifestyle Both Play a Role
Type 2 diabetes requires two ingredients: a genetic predisposition and an environmental trigger. Genes alone aren’t enough. When one identical twin develops type 2 diabetes, the other twin’s lifetime risk tops out at about 75%, which confirms a strong genetic component but also shows that something else has to tip the balance.
That “something else” is usually a combination of excess body weight, physical inactivity, and diet. Carrying extra fat, especially around the midsection, makes cells more resistant to insulin. Men with a waist circumference over 40 inches and women over 35 inches face elevated risk regardless of their overall body weight. A BMI of 25 or higher increases risk for most adults, though the threshold is lower for Asian Americans (BMI 23) and slightly higher for Pacific Islanders (BMI 26).
Other major risk factors include being over 35, having a parent or sibling with the disease, a history of gestational diabetes, and living a sedentary lifestyle. The condition is also more common in men than women and in urban populations compared to rural ones.
How It’s Diagnosed
Doctors use one of three blood tests, and any of them can confirm a diagnosis:
- A1C test: Measures your average blood sugar over the past two to three months. Normal is below 5.7%, prediabetes falls between 5.7% and 6.4%, and diabetes is diagnosed at 6.5% or higher.
- Fasting blood glucose: Taken after an overnight fast. Normal is below 100 mg/dL, prediabetes is 100–125 mg/dL, and 126 mg/dL or higher indicates diabetes.
- Oral glucose tolerance test: Measures blood sugar two hours after drinking a sugary solution. Normal is below 140 mg/dL, prediabetes is 140–199 mg/dL, and 200 mg/dL or higher means diabetes.
A single abnormal result is typically confirmed with a repeat test before a formal diagnosis is made.
What It Does to Your Body Over Time
Persistently high blood sugar damages blood vessels, and the consequences show up in two broad categories. Small-vessel damage affects the eyes, kidneys, and nerves. Large-vessel damage accelerates heart disease and stroke.
In the eyes, high blood sugar weakens the tiny capillaries of the retina, causing them to leak or grow abnormally. This is called diabetic retinopathy, and it’s a leading cause of vision loss in adults. In the kidneys, the filtering units gradually break down, allowing protein to spill into the urine. Left unchecked, this progresses to kidney failure. Nerve damage, especially in the feet and legs, can cause numbness, tingling, or pain and raises the risk of foot ulcers and infections that heal poorly.
On the cardiovascular side, people with type 2 diabetes face roughly double the risk of heart attack and stroke compared to those without the condition. The combination of high blood sugar, high blood pressure, and abnormal cholesterol levels (all common in type 2 diabetes) accelerates the buildup of plaque in arteries throughout the body.
The good news is that every one of these complications is slower to develop, and less severe, when blood sugar stays closer to normal. Complications aren’t inevitable.
Treatment Options
The first treatment for nearly everyone is lifestyle change: more physical activity, a healthier eating pattern, and weight loss if needed. When medication is required, the starting point is almost always metformin. It works by reducing the amount of sugar your liver releases into the bloodstream and by making your muscle cells more responsive to insulin. It’s been used for decades, is inexpensive, and is well tolerated by most people.
If metformin alone isn’t enough, newer medication classes offer additional benefits beyond blood sugar control. One group, GLP-1 receptor agonists (delivered by injection or taken orally), mimics a gut hormone that stimulates insulin release after meals. These medications often produce meaningful weight loss and some have been shown to reduce the risk of heart disease. Another class, SGLT2 inhibitors, works by causing excess sugar to be filtered out through the kidneys into your urine. They also lower blood pressure slightly and have proven benefits for people with heart failure or kidney disease.
Some people eventually need insulin injections, particularly if the pancreas’s ability to produce insulin has declined significantly. Treatment is highly individual and often changes over time as the condition progresses or responds to lifestyle modifications.
Prevention Works Better Than You’d Expect
The landmark Diabetes Prevention Program study remains one of the most convincing pieces of evidence in all of preventive medicine. Participants at high risk for type 2 diabetes who made moderate lifestyle changes (targeting 7% body weight loss and 150 minutes of physical activity per week) cut their risk of developing diabetes by 58% over about three years. Every kilogram of weight lost reduced the risk by 16%. Even metformin, given without lifestyle changes, reduced risk by 31%. The study was actually ended early because the results were so clear.
These findings hold particular weight because the participants already had prediabetes. The benefits weren’t theoretical or limited to healthy people making marginal improvements. They were measured in people on the doorstep of a diagnosis.
Remission Is Possible for Some People
Type 2 diabetes was long considered a one-way diagnosis, but that view has shifted. A 2021 consensus statement from an international group of diabetes experts formally defined remission as achieving an A1C below 6.5% that lasts at least three months after stopping all blood sugar-lowering medications.
Remission is most achievable early in the disease, before the insulin-producing cells of the pancreas have sustained too much damage. It typically requires significant weight loss, whether through dietary changes, structured programs, or bariatric surgery. Remission doesn’t mean the disease is cured. The underlying predisposition remains, blood sugar can rise again over time, and yearly monitoring is still recommended. But for people who achieve it, it represents a meaningful period of reduced risk and fewer medications.