Diabetes explained: type 1, type 2, symptoms and prevention

What goes wrong: insulin and blood sugar

Glucose, the sugar formed from food, is the body's main fuel, especially for the brain and muscles. After eating, blood glucose rises, and the pancreas releases insulin, which helps cells take glucose in and brings blood sugar back down. In diabetes this control fails in one of two ways: either insulin production falls short, or the body's cells stop responding properly to the insulin that is there.

The result in both cases is hyperglycaemia, persistently raised blood sugar. In the short term it causes thirst, frequent urination and fatigue; over years it injures small and large blood vessels, which is why diabetes is a leading cause of blindness, kidney failure, heart attacks, strokes and lower-limb amputation.

Type 1, type 2 and gestational diabetes

Type 1 diabetes is an autoimmune condition in which the body's immune system destroys the insulin-producing cells of the pancreas, so insulin production stops. It is the most common type in children and young adults but can occur at any age, it requires daily insulin for survival, and neither its cause nor a way to prevent it is currently known. Its symptoms usually appear quickly, over days to weeks, and can include nausea, vomiting or rapid breathing when blood sugar is very high.

Type 2 diabetes, by contrast, develops when the body uses insulin ineffectively and gradually cannot produce enough of it. More than 95% of people with diabetes have type 2, which is linked to genetics, ageing, excess body weight and physical inactivity. Its symptoms are often milder and may take years to notice, so it is frequently diagnosed only after complications have begun. Once seen only in adults, it is now occurring increasingly in children. Gestational diabetes is raised blood sugar first recognised during pregnancy; it usually settles after delivery, but mother and child carry a higher later risk of type 2.

Symptoms, diagnosis and treatment

The classic warning signs, shared by both main types, are feeling very thirsty or hungry, urinating often, extreme fatigue, blurred vision and unexplained weight loss. In type 1 these tend to be sudden and pronounced; in type 2 they are often less marked, which is why regular blood sugar testing matters for people at risk.

Diagnosis rests on blood glucose measurements: fasting plasma glucose after an overnight fast, the oral glucose tolerance test before and after a glucose drink, HbA1c, which reflects average blood sugar over the past two to three months, or a random glucose test when classic symptoms are present. Treatment depends on the type but generally combines healthy eating, regular physical activity, blood sugar monitoring, medicines (insulin for type 1; oral and sometimes injectable medicines, and possibly insulin, for type 2), control of blood pressure and cholesterol, and regular screening of eyes, kidneys, nerves and feet.

Prevention: what can and cannot be avoided

Type 1 diabetes cannot currently be prevented. Type 2, however, can often be prevented or delayed, especially in people at increased risk, through regular physical activity, a healthy diet that limits excess energy, sugar and unhealthy fats, maintaining a healthy body weight, and avoiding tobacco. Health systems also play a part, through early detection, affordable diagnostics and long-term follow-up in primary care.

The scale is large and growing: in the Americas alone, the number of adults living with diabetes has tripled since 1990, and worldwide the disease's death toll has risen by more than half in twenty years, with much of the burden falling on low- and middle-income countries. Early diagnosis is the single most important step, because the longer diabetes goes undetected and untreated, the worse the outcomes. This article gives general educational information only, not personal medical advice.

Editorial disclosure

This article was researched and published with AI assistance. No human prepublication review is claimed. Report factual errors through our contact page.