What Is Type 2 Diabetes? How Insulin Resistance Raises Blood Sugar

Every cell in your body runs partly on glucose, a simple sugar that comes mainly from the carbohydrates you eat. Glucose travels in your bloodstream, but it cannot simply walk into your cells. It needs a helper. That helper is insulin, a hormone made by the beta cells of your pancreas.

Type 2 diabetes is what happens when that system stops working smoothly. It is the most common form of diabetes by far, accounting for over 90% of cases worldwide.

Insulin: the key that opens the door

A simple way to picture insulin is as a key. After a meal, your blood sugar rises and your pancreas releases insulin. Insulin attaches to cells in your muscles, fat and liver and “unlocks” them, so glucose can move inside to be used for energy or stored for later. As glucose leaves the blood, blood sugar falls back to normal.

Insulin also tells your liver to stop releasing its own stored sugar. Between meals and overnight, the liver keeps blood sugar steady by releasing small amounts. After you eat, insulin signals it to pause.

What goes wrong in type 2 diabetes

Two problems develop together, usually over many years.

1. Insulin resistance. The “locks” on your cells become stiff. Muscle, liver and fat cells respond less to insulin, so more insulin is needed to move the same amount of glucose. Extra fat stored in and around the liver, pancreas and abdominal organs (visceral fat), physical inactivity, poor sleep, some medicines and your genes all contribute. We explain the causes in more detail in What Causes Prediabetes? Insulin Resistance Explained.

2. Beta-cell decline. For a long time, the pancreas copes by making more and more insulin. Blood sugar stays normal or only slightly raised. Eventually, the beta cells cannot keep up. Their output falls, blood sugar climbs into the prediabetes range and then into the diabetes range.

Other organs join in. The liver keeps releasing sugar even when it should not. The gut makes less of the hormones (incretins) that normally boost insulin after meals. The kidneys hold on to more glucose. This is why several different medicines, each acting on a different organ, can help.

How common is it?

Source: IDF Diabetes Atlas, 11th edition (2025).

In the United States, about 16% of adults have diabetes, and more than a quarter of them have not been diagnosed (CDC, 2021–2023 data).

Type 2 vs type 1: what is the difference?

Why high blood sugar matters

Blood sugar that stays high for years slowly damages blood vessels, large and small. The small vessels in the eyes, kidneys and nerves are especially sensitive, and so are the large arteries that supply the heart and brain. That is why type 2 diabetes raises the risk of heart attack, stroke, kidney disease, vision loss and nerve damage in the feet.

The encouraging part is that this damage is largely preventable. Large studies, such as the UK Prospective Diabetes Study, showed that bringing blood sugar, blood pressure and cholesterol closer to target cuts the risk of complications substantially. You can read more in Preventing Long-Term Complications.

Is it the same as prediabetes?

No. Prediabetes means blood sugar is higher than normal but not yet in the diabetes range. It is the stage before type 2 diabetes, and it is the best time to act, because lifestyle changes can often bring blood sugar back to normal. If you have been told you have prediabetes, start with What Is Prediabetes? A Simple Introduction and our complete prediabetes guide.

Can type 2 diabetes go away?

Type 2 diabetes is usually a long-term condition, and for most people it gradually changes over time. However, some people, particularly those diagnosed recently who lose a significant amount of weight, can bring their blood sugar back below the diabetes range without medicines. Experts call this remission rather than cure, because blood sugar can rise again, so regular check-ups remain important.

Common questions