Diabetes is not one disease. It is a group of conditions that all end in the same place — too much glucose circulating in the blood — but that get there by different routes. The route matters, because it decides the treatment.
Glucose and insulin, in one paragraph
Almost everything you eat that contains carbohydrate is broken down into glucose, which enters the bloodstream. Glucose is fuel, but cells cannot absorb it on their own. They need insulin, a hormone made by beta cells in the pancreas, which acts like a key opening the door. When that system works, blood glucose stays in a narrow band all day, whether you have just eaten or not eaten for twelve hours.
Type 1
The immune system mistakenly destroys the beta cells. The pancreas stops making insulin — not less of it, but essentially none. This usually appears in childhood or early adulthood, though it can start at any age, and it comes on over weeks rather than years. Because the body makes no insulin at all, insulin has to be replaced from outside, for life. There is nothing anyone did to cause it and nothing in diet or lifestyle that prevents it.
Type 2
Two things go wrong together. Cells become resistant to insulin, so the same amount of insulin moves less glucose. The pancreas compensates by making more, and for years it manages. Eventually it cannot keep up, and glucose starts to rise. This is the form that accounts for roughly nine in ten cases. It develops slowly and quietly, which is why many people are diagnosed only when a routine test picks it up — or when a complication does.
Type 2 is strongly influenced by weight, activity, and genetics, and the genetic part is significant. Plenty of people who have never been overweight develop it. Treatment usually starts with diet, activity and tablets such as metformin, and may progress to injectable medication or insulin. Progression is not a personal failure — it reflects the natural course of the condition.
Gestational diabetes
High glucose that appears during pregnancy in someone who did not have diabetes before. Pregnancy hormones cause insulin resistance; in some women the pancreas cannot compensate. It usually resolves after delivery, but it is a strong signal of future type 2 risk, so it is worth re-testing yearly afterwards.
Prediabetes
Glucose above normal but below the threshold for diabetes. It is a warning, not a verdict. Studies consistently show that structured changes in diet and activity at this stage reduce the risk of progressing to type 2 by roughly half — a bigger effect than most medications achieve.
How it is diagnosed
Any one of these, confirmed on a second test:
- Fasting plasma glucose of 126 mg/dL (7.0 mmol/L) or higher
- HbA1c of 6.5% or higher
- A two-hour value of 200 mg/dL (11.1 mmol/L) or higher during an oral glucose tolerance test
- A random glucose of 200 mg/dL (11.1 mmol/L) or higher together with classic symptoms
Symptoms worth acting on
Unusual thirst, urinating far more than normal, unexplained weight loss, persistent fatigue, blurred vision, cuts that heal slowly, recurrent infections. In type 1 these arrive fast and are hard to ignore. In type 2 they can be so gradual that they get attributed to age or to a busy season of life.
If you are unsure which type you have — and it happens more often than you would expect, particularly in adults diagnosed with type 2 who turn out to have slow-onset type 1 — ask your doctor. Antibody testing and a C-peptide level can settle it, and the answer changes the treatment plan.