Diabetes is a group of conditions where your blood sugar stays too high because your body can’t properly make or use insulin, the hormone that moves sugar from your bloodstream into your cells for energy. About 15.8% of U.S. adults have some form of diabetes, and roughly 4.5% of those don’t know it yet.
How Insulin Normally Works
When you eat, your body breaks down carbohydrates into glucose, a simple sugar that enters your bloodstream. Your pancreas detects the rising blood sugar and releases insulin in response. Insulin acts like a key: it binds to receptors on the surface of your muscle and fat cells, triggering those cells to open specialized channels that pull glucose inside. Your muscles use glucose immediately for energy or store it for later. This whole process keeps blood sugar within a tight, healthy range.
In diabetes, this system breaks down. Either the pancreas stops producing enough insulin, or the cells stop responding to it properly, or both. Without that signal, glucose builds up in the bloodstream instead of entering cells. The result is chronically high blood sugar, which over time damages blood vessels, nerves, and organs throughout the body.
Type 1 Diabetes
Type 1 diabetes is an autoimmune condition. The immune system mistakenly attacks and destroys the insulin-producing cells in the pancreas. Once enough of those cells are gone, the body can no longer make meaningful amounts of insulin on its own. People with type 1 need to take insulin every day to survive, either through injections or an insulin pump.
Type 1 accounts for roughly 1% of the population in developed countries. It typically appears in childhood or adolescence, though it can develop at any age. The onset is often rapid, with symptoms appearing over weeks rather than years. Because insulin production drops quickly, type 1 tends to cause more dramatic early symptoms than type 2.
Type 2 Diabetes
Type 2 is far more common, affecting about 8.5% of the global adult population. It starts with insulin resistance: your cells, particularly in muscle and fat tissue, stop responding efficiently to insulin. The pancreas compensates by producing more insulin, but eventually it can’t keep up. Blood sugar rises, and over time the insulin-producing cells themselves may begin to fail.
The causes are a mix of genetics and lifestyle. Researchers have identified at least 150 DNA variations linked to type 2 risk, many of which subtly affect how the pancreas develops, how insulin is released, or how sensitive cells are to insulin’s signal. But genes alone rarely cause the disease. Excess weight, physical inactivity, smoking, and a poor diet all amplify the genetic risk. Most people develop some degree of insulin resistance as they age, but carrying extra weight and not exercising make it significantly worse.
Gestational Diabetes
Some women develop diabetes during pregnancy, typically around the 24th week. Screening usually happens between weeks 24 and 28, though women at higher risk may be tested earlier. Gestational diabetes usually resolves after delivery, but it signals a significant long-term risk: about half of women who have it go on to develop type 2 diabetes later in life.
Prediabetes: The Warning Stage
Before type 2 diabetes fully develops, most people pass through a stage called prediabetes, where blood sugar is higher than normal but not yet high enough for a diabetes diagnosis. This stage is reversible. In one study tracking adults with prediabetes over five years, those who received lifestyle counseling (focused on diet, exercise, and weight loss) saw strong results: 42.8% returned to normal blood sugar levels, 50% stayed in the prediabetes range without getting worse, and only 7.2% progressed to type 2 diabetes. Overall, about 93% of participants who started lifestyle changes within a few years of developing prediabetes did not progress to diabetes during the follow-up period.
The key interventions are straightforward: losing a moderate amount of weight, increasing physical activity, and improving your diet. These changes directly reduce insulin resistance, giving your pancreas a chance to keep blood sugar controlled.
Common Symptoms
High blood sugar produces a recognizable set of symptoms. When glucose builds up in the blood, your kidneys work harder to filter it out, pulling extra water along with it. This creates a cycle: you urinate more frequently, which makes you dehydrated, which makes you intensely thirsty. Other common signs include unexplained weight loss (especially in type 1), blurred vision, slow-healing cuts, fatigue, and tingling or numbness in the hands or feet.
Type 1 symptoms tend to come on suddenly and severely. Type 2 often develops so gradually that people live with elevated blood sugar for years without noticing. That’s why nearly a third of people with diabetes in the U.S. are undiagnosed.
How Diabetes Is Diagnosed
Doctors use a few standard blood tests. The most common is the A1C test, which measures your average blood sugar over the past two to three months. An A1C of 6.5% or higher indicates diabetes. A fasting blood sugar test (taken after at least eight hours without eating) of 126 mg/dL or higher also qualifies. A third option is a glucose tolerance test, where you drink a sugary solution and your blood sugar is measured two hours later; a reading of 200 mg/dL or higher means diabetes. If you’re already showing classic symptoms like excessive thirst and frequent urination, a random blood sugar reading of 200 mg/dL or above at any time of day is enough for diagnosis.
What High Blood Sugar Does Over Time
Chronically elevated blood sugar damages blood vessels in two ways: it harms the tiny vessels (microvascular damage) and the larger ones (macrovascular damage). The combination affects nearly every major organ system, and roughly one third to one half of people with diabetes eventually develop some form of these complications.
Small-vessel damage shows up in three main areas. In the eyes, it causes diabetic retinopathy, a leading cause of blindness. In the kidneys, it gradually impairs their ability to filter waste from the blood. In the nerves, particularly in the feet and hands, it causes numbness, tingling, and pain, a condition called neuropathy that can eventually lead to serious infections or the need for amputation.
Large-vessel damage increases the risk of heart disease, stroke, and poor circulation in the legs. Heart disease is the leading cause of death among people with diabetes, not because diabetes directly attacks the heart, but because high blood sugar accelerates the buildup of plaque in arteries throughout the body.
Managing Blood Sugar
The core goal for all types of diabetes is keeping blood sugar as close to a normal range as possible. How that’s achieved depends on the type.
People with type 1 diabetes rely on insulin therapy, carefully matching their insulin doses to the food they eat and their activity levels. Continuous glucose monitors and insulin pumps have made this process more precise, but it still requires daily attention.
For type 2, treatment usually starts with lifestyle changes: improving diet, increasing exercise, and losing weight. These directly reduce insulin resistance, which is the root problem. When lifestyle changes aren’t enough, oral medications that help the body use insulin more effectively or reduce glucose production are typically the next step. Some people with type 2 eventually need insulin as well, particularly if the condition progresses and the pancreas produces less insulin over time.
Regardless of type, regular monitoring matters. Tracking your blood sugar, keeping A1C in a target range, and staying on top of eye exams, kidney function tests, and foot checks can catch complications early, when they’re most treatable.