What is type 2 diabetes?

Type 2 diabetes accounts for about 90% of all diabetes cases, making it by far the most common form of this chronic disease — and one of the most receptive to prevention, contrary to what one might think.

A different mechanism from type 1 diabetes

Diabetes, in any form, is characterized by persistently high blood sugar (glucose). But the underlying mechanisms differ markedly between the two main types. Type 1 diabetes, usually diagnosed in children or young adults, results from an autoimmune reaction destroying the insulin-producing cells of the pancreas — it generally appears fairly quickly and isn't linked to lifestyle. Type 2 diabetes, on the other hand, most often develops gradually in adulthood: the pancreas keeps producing insulin, sometimes even in excess at first, but the body becomes progressively less able to use it effectively — a phenomenon called insulin resistance, which eventually exhausts the pancreas's ability to compensate.

A rising prevalence, everywhere in the world

In France, about 4.1 million adults are affected by diabetes, with type 2 diabetes accounting for the vast majority of these cases. In the United States, that figure reaches about 38.5 million adults, roughly one in six or seven people depending on age group (CDC 2024 data). Globally, according to the World Health Organization, the number of people living with diabetes rose from 200 million in 1990 to about 830 million in 2022 — a rise largely linked to urbanization, changing eating habits, and increasing sedentary lifestyles. One figure especially worth remembering, found in comparable proportions in both France and the United States: nearly one in four people with diabetes is still unaware of their diagnosis, for lack of screening.

Prediabetes, a warning sign too often overlooked

Before full-blown type 2 diabetes, there is often an intermediate stage called prediabetes — blood sugar already above normal, but not yet at the diagnostic threshold for diabetes. This stage affects more than one in ten adults in France, and represents a valuable window for action: at this stage, lifestyle changes can still prevent or significantly delay progression to full diabetes, a point covered in more detail in this blog's last article.

How is it diagnosed?

Diagnosis relies on a blood test, never on a questionnaire or on symptoms alone. In France, as in the World Health Organization's (WHO) recommendations, diabetes is diagnosed when fasting blood glucose reaches or exceeds 1.26 g/L (7 mmol/L) on two occasions, or when blood glucose measured at any time of day exceeds 2 g/L in the presence of symptoms. Glycated hemoglobin (HbA1c), which reflects average blood sugar over the past two to three months, is also used: a result of 6.5% or higher points to diabetes.

Prediabetes thresholds vary by country, which partly explains the gap in figures between France and the United States. In France and according to the WHO, impaired fasting glucose is defined as 1.10 to 1.25 g/L. The American Diabetes Association uses a lower threshold, starting at 1.00 g/L, or an HbA1c between 5.7% and 6.4%. With this broader definition, about one in three American adults would be affected by prediabetes according to the CDC, and the vast majority are unaware of it.

There are also other, less common forms of diabetes: gestational diabetes, which appears during pregnancy and raises the risk of type 2 diabetes later on, certain rare genetic forms, and a late-onset autoimmune form in adults, sometimes initially mistaken for type 2 diabetes. This is one more reason to let a doctor interpret the results and clarify the type of diabetes involved.

Why does type 2 diabetes develop?

Several factors contribute to the development of type 2 diabetes, often in combination: a genetic predisposition (risk is higher with a direct family history), excess weight and obesity, particularly abdominal, a sedentary lifestyle, and age, with risk increasing after 45. Contrary to a sometimes widespread belief, type 2 diabetes is never the result of a single isolated factor — it is the combination of several elements, some of them modifiable, that determines individual risk, a principle similar to that of overall cardiovascular risk already covered on another blog on this site.

Why early screening matters

Unlike type 1 diabetes, which usually shows up quickly and clearly, type 2 diabetes often develops silently, sometimes for years, before being diagnosed — which largely explains the proportion of undiagnosed cases. In France, screening via fasting blood glucose or glycated hemoglobin (HbA1c) is recommended every 3 years from age 45 for people with risk factors. A screening tool like the FINDRISC score, based on simple criteria (age, waist circumference, physical activity, family history...), allows you to estimate this risk without waiting for a blood test, offering a first indication accessible to everyone before even considering a blood panel.

A disease with multiple consequences if left unmanaged

Uncontrolled type 2 diabetes can, over time, affect many organs: the eyes (diabetic retinopathy, the leading cause of preventable blindness in adults in many countries), the kidneys (diabetic nephropathy), the nerves (neuropathy, which can affect sensation in the feet in particular), and of course the cardiovascular system, a topic covered in detail in another article on this blog. This range of potential complications explains why caring for someone with diabetes usually involves several healthcare professionals, coordinated around the primary care doctor.

A diagnosis that isn't a life sentence

Receiving a type 2 diabetes diagnosis, however daunting it may seem at first, in no way means an irreversibly upended life. Many people with type 2 diabetes live perfectly normal lives, with good blood sugar control achieved through lifestyle adjustments, sometimes combined with medication. The key lies in appropriate care and regular follow-up, rather than an anxiety-driven approach to the diagnosis itself.

The role of genetics, without making it inevitable

Having a parent or sibling with type 2 diabetes significantly raises a person's own risk of developing the disease, a finding that reflects both a real genetic component and lifestyle habits often shared within the same family. This predisposition, however, doesn't mean type 2 diabetes is inevitable for the people concerned — it instead justifies greater vigilance and earlier screening, in a context where, as mentioned earlier, prevention has shown real effectiveness, particularly at the prediabetes stage.

To estimate your own risk level, take the “Am I at risk of diabetes?” test.