People get diabetes through several different pathways depending on the type. In type 2 diabetes, which accounts for roughly 90% of all cases, the body’s cells gradually stop responding to insulin, usually driven by excess weight and inactivity. In type 1 diabetes, the immune system destroys the cells that make insulin. Other forms develop during pregnancy or from inherited gene mutations. As of 2024, about 589 million adults worldwide have diabetes, roughly one in nine.
Type 2: Insulin Resistance Builds Over Time
Type 2 diabetes develops when your muscle, fat, and liver cells stop responding properly to insulin. Insulin is the hormone that tells cells to absorb sugar from your blood. When cells resist that signal, sugar stays in the bloodstream and levels climb. Your pancreas compensates by pumping out more and more insulin, but eventually it can’t keep up. At that point, blood sugar rises high enough to cause damage.
The resistance starts at a cellular level. Excess body fat, particularly the deep abdominal fat surrounding your organs, releases inflammatory chemicals that interfere with insulin’s ability to do its job. These inflammatory signals disrupt the chain of events that normally moves sugar from the blood into muscle cells. At the same time, the liver begins producing more fat on its own, and fatty acids circulating in the blood start depositing in tissues where fat doesn’t belong, like the liver and muscles. This ectopic fat further worsens insulin resistance.
The pancreas tries to compensate by overproducing insulin. In younger people especially, this extra demand on insulin-producing cells accelerates their burnout. What begins as a compensatory response eventually leads to permanent loss of the pancreas’s ability to make enough insulin. This is why type 2 diabetes tends to get progressively harder to manage over time.
What Drives Type 2 Risk
Excess weight is the single biggest modifiable risk factor. Visceral fat, the kind packed around abdominal organs, is particularly harmful because it attracts immune cells called macrophages. These macrophages release inflammatory compounds that directly impair insulin signaling in nearby and distant tissues. This is why waist circumference is a better predictor of diabetes risk than overall body weight alone.
Physical inactivity compounds the problem. Muscle tissue is the largest consumer of blood sugar in the body, and regular movement keeps those cells sensitive to insulin. A sedentary lifestyle lets resistance build unchecked. Diet plays a role too, particularly diets high in refined carbohydrates and sugary drinks that create repeated blood sugar spikes.
Genetics load the gun, but lifestyle pulls the trigger. Over 65 genetic variants have been identified that increase type 2 risk, though each one only raises it by about 10 to 35%. Even combining multiple risk variants into a genetic score only predicts a 10 to 12% increased chance of developing the disease. Family history matters, but it’s far from destiny. Rates are higher in urban areas (12.3%) than rural ones (9.2%), likely reflecting differences in diet and activity levels. Middle-income countries carry the highest burden globally at 11.5% prevalence, suggesting that the shift toward processed food and sedentary work is a powerful driver.
Certain racial and ethnic minority groups have historically higher rates of diabetes, a gap that hasn’t substantially narrowed. Much of this disparity traces back to social determinants of health: the conditions in places where people live, learn, work, and eat. These social factors account for 50 to 60% of health outcomes overall.
Type 1: The Immune System Attacks
Type 1 diabetes is an autoimmune disease. The body’s own immune cells infiltrate the pancreas and destroy the beta cells responsible for producing insulin. Both types of T cells, the immune system’s targeted killers, are required to effectively carry out this destruction. CD8 T cells differentiate into cytotoxic lymphocytes that directly kill beta cells through toxic chemicals and molecular death signals. Macrophages are the first immune cells to arrive in the pancreas during the attack and are the most abundant.
Once enough beta cells are destroyed, the body can no longer produce sufficient insulin. Blood sugar rises uncontrollably, and the person requires lifelong insulin therapy. This process typically happens in childhood or adolescence, though it can occur at any age.
Unlike type 2, type 1 has nothing to do with weight or lifestyle. The trigger appears to be a combination of genetic susceptibility and an environmental event that sets the immune system off course. Viral infections are the leading suspected trigger. Enteroviruses, particularly a group called coxsackievirus B types 1 through 6, have the strongest evidence linking them to the onset of islet autoimmunity. The theory is that these viruses may infect or damage pancreatic tissue in a way that draws the immune system’s attention, and in genetically predisposed individuals, the immune response never shuts off.
Gestational Diabetes During Pregnancy
Some women develop diabetes during pregnancy even with no prior history. The placenta produces hormones, including estrogen, cortisol, and human placental lactogen, that progressively block insulin’s effects. This “contra-insulin” effect typically begins around 20 to 24 weeks of pregnancy. As the placenta grows larger, it produces more of these hormones, and insulin resistance increases.
Most women’s pancreases can ramp up insulin production enough to overcome this resistance. But for some, particularly those who already had borderline insulin sensitivity before pregnancy, the added demand is too much. Blood sugar rises and gestational diabetes is diagnosed. It usually resolves after delivery when the placenta is gone, but it signals a significantly higher risk of developing type 2 diabetes later in life.
LADA and MODY: Less Common Pathways
Not every case of diabetes fits neatly into type 1 or type 2. Latent autoimmune diabetes in adults (LADA) is sometimes called “type 1.5.” It involves the same autoimmune destruction of insulin-producing cells as type 1, but it progresses much more slowly. People with LADA are typically diagnosed as adults, and they don’t need insulin for at least six months after diagnosis. It’s identified by testing for specific autoantibodies in the blood. Many people with LADA are initially misdiagnosed with type 2 because of their age.
Maturity-onset diabetes of the young (MODY) is caused by a single gene mutation inherited from a parent. Unlike the dozens of small-effect genetic variants behind type 2, MODY results from one defective gene that directly disrupts how the pancreas senses blood sugar or produces insulin. The most common forms involve mutations in the glucokinase gene, which acts as the pancreas’s blood sugar sensor, or in genes that control how beta cells develop and function. MODY typically appears before age 25 and runs strongly in families, with each child of an affected parent having a 50% chance of inheriting the mutation.
How Prediabetes Leads to Full Diabetes
Type 2 diabetes rarely appears out of nowhere. Most people pass through a stage called prediabetes, where blood sugar is higher than normal but not yet in the diabetic range. During this phase, insulin resistance is already established and the pancreas is working overtime. The transition from prediabetes to diabetes is not inevitable. Weight loss of even 5 to 7% of body weight and regular physical activity can significantly slow or prevent progression.
What makes prediabetes dangerous is that it’s silent. There are no obvious symptoms, so many people don’t know they have it until a routine blood test picks it up. By the time type 2 diabetes is diagnosed, the pancreas may have already lost a substantial portion of its insulin-producing capacity. This is why screening matters, especially if you carry risk factors like excess abdominal weight, a sedentary lifestyle, a family history of diabetes, or membership in a higher-risk ethnic group.