Diabetes is a condition where your blood sugar (glucose) stays too high because your body either can’t make enough insulin or can’t use the insulin it produces. Insulin is a hormone from your pancreas that acts like a key, unlocking your cells so glucose from food can enter and be used for energy. When that system breaks down, sugar builds up in your bloodstream and starves your cells of fuel at the same time. Over time, that excess sugar damages blood vessels and organs throughout the body.
How Blood Sugar Regulation Works
Every time you eat, your digestive system breaks carbohydrates down into glucose, which enters your bloodstream. Your pancreas detects this rise in blood sugar and releases insulin in response. Insulin signals cells in your muscles, liver, and fat tissue to absorb that glucose and either use it immediately for energy or store it for later. In a healthy body, this cycle keeps blood sugar within a narrow range throughout the day.
In diabetes, this process fails at one or both stages. Either the pancreas stops producing enough insulin, or your cells stop responding to the insulin that’s there. The result is the same: glucose accumulates in the blood while your tissues can’t access the energy they need.
Type 1 Diabetes
Type 1 diabetes is an autoimmune disease. Your immune system mistakenly attacks and destroys the insulin-producing cells in the pancreas (called beta cells), leaving your body with little to no insulin. This form typically appears in childhood or adolescence, though it can develop at any age. Because the beta cells are gone, people with type 1 diabetes need to take insulin every day for the rest of their lives. The exact trigger is still unclear, but it involves a combination of genetic susceptibility and environmental factors.
Type 2 Diabetes
Type 2 diabetes is far more common and develops differently. It starts with insulin resistance: your muscle, liver, and fat cells gradually stop responding properly to insulin. Your pancreas compensates by producing more, but over time it can’t keep up, and blood sugar rises. A combination of factors drives this process. A high-fat diet and excess body fat can trigger chronic low-grade inflammation throughout the body. Fat tissue becomes dysfunctional and releases inflammatory signals that further worsen insulin resistance, creating a cycle that’s hard to break without intervention.
Multiple organs play a role in type 2 diabetes, not just the pancreas. The liver, skeletal muscles, kidneys, brain, small intestine, and fat tissue all contribute to how your body handles glucose. If left unmanaged long enough, the pancreas’s insulin-producing cells can fail permanently.
Gestational Diabetes
Some people develop diabetes for the first time during pregnancy. Gestational diabetes occurs when hormonal changes make your body more resistant to insulin, and your pancreas can’t compensate. In the U.S., screening typically happens at 24 to 28 weeks of pregnancy using a glucose tolerance test, where you drink a sugary solution and have your blood drawn at timed intervals. Gestational diabetes usually resolves after delivery, but it significantly increases the risk of developing type 2 diabetes later in life.
The Three Classic Warning Signs
Diabetes produces three hallmark symptoms, sometimes called the “three Ps”:
- Excessive thirst. High blood sugar pulls fluid from your tissues, leaving you dehydrated and constantly thirsty.
- Frequent urination. Your kidneys work overtime to filter the excess glucose, producing more urine than usual.
- Extreme hunger. Because your cells can’t absorb glucose properly, your body signals that it needs more fuel, even if you’ve just eaten.
Other common signs include unexplained weight loss (especially in type 1), fatigue, blurred vision, and slow-healing wounds. Type 2 diabetes often develops gradually enough that symptoms go unnoticed for years, which is why blood tests are so important.
Prediabetes: The Warning Stage
Before type 2 diabetes fully develops, most people pass through a stage called prediabetes. Your blood sugar is higher than normal but not yet high enough to qualify as diabetes. The numbers fall in a specific middle zone: a fasting blood sugar between 100 and 125 mg/dL, or an A1C (a measure of your average blood sugar over roughly three months) between 5.7% and 6.4%. For comparison, a diabetes diagnosis requires a fasting blood sugar of 126 mg/dL or higher, or an A1C of 6.5% or above.
Prediabetes is not a harmless label. Without lifestyle changes, many people with prediabetes develop type 2 diabetes within five years. The good news is that this stage is often reversible with increased physical activity, dietary changes, and modest weight loss.
What Happens to Your Body Over Time
The real danger of diabetes lies in what chronically high blood sugar does to your blood vessels. Damage falls into two categories: small-vessel and large-vessel complications.
Small-vessel damage produces three conditions unique to diabetes. Retinopathy affects the eyes, where tiny blood vessels in the retina weaken, leak, or grow abnormally. New vessels that form are fragile and can rupture, causing bleeding inside the eye. Fluid can also accumulate in the central part of the retina, distorting vision. Nephropathy affects the kidneys, where filtering structures gradually scar and lose function. In severe cases, this progresses to kidney failure. Neuropathy, the most common complication, damages nerves, particularly in the feet and legs. It can cause numbness, tingling, pain, and eventually foot deformities and ulcers that heal poorly.
Large-vessel damage accelerates the same kind of artery disease that causes heart attacks and strokes. People with diabetes face significantly higher cardiovascular risk, and kidney damage from diabetes further compounds that risk. Heart disease remains the leading cause of death among people with diabetes.
How Diabetes Is Diagnosed
Doctors use three main blood tests to diagnose diabetes. You only need one abnormal result (confirmed on a second occasion) for a diagnosis:
- A1C test. Measures your average blood sugar over the past two to three months. A result of 6.5% or higher indicates diabetes.
- Fasting blood sugar. Taken after at least eight hours without eating. A level of 126 mg/dL or higher indicates diabetes.
- Oral glucose tolerance test. Measures blood sugar two hours after drinking a glucose solution. A level of 200 mg/dL or higher indicates diabetes.
Living With Diabetes Day to Day
Managing diabetes centers on keeping blood sugar as close to a normal range as possible. For type 1, that means taking insulin (through injections or a pump) and carefully matching doses to food intake and activity. For type 2, management often starts with lifestyle changes and oral medications, though some people eventually need insulin as well.
Monitoring blood sugar is a daily reality. Traditional finger-stick meters give you a single reading at a moment in time. Continuous glucose monitors (CGMs), which use a small sensor worn on the skin, track glucose levels around the clock and send readings to a phone or receiver every few minutes. CGMs help people spot patterns, catch dangerous lows before they become emergencies, and reduce the number of finger sticks needed each day. Some models still require occasional finger-stick tests to confirm accuracy, especially when adjusting insulin doses.
Diet and exercise are not just add-ons to medication. Physical activity directly helps your cells absorb glucose more efficiently, and choosing foods that raise blood sugar more slowly (whole grains, vegetables, lean proteins) makes the entire management process easier. For people with type 2 diabetes or prediabetes, these changes can sometimes reduce or eliminate the need for medication entirely.