Causes of Diabetes

Type 1 and type 2 diabetes, the two most common forms of diabetes, are characterized by elevated blood sugar. However, the underlying mechanisms and causes of high blood sugar in these forms of diabetes are quite different.

Type 1 diabetes is an autoimmune disease in which the body’s immune system malfunctions and attacks the beta cells of the pancreas, the cells that produce insulin, the hormone that enables cells of the body to use glucose. Therefore, a person with type 1 diabetes has abnormally high blood glucose because their body no longer produces a sufficient amount of insulin.

The disease process at work in type 2 diabetes differs from what we see with type 1 diabetes. In type 2 diabetes, we depend on the action of several different hormones, including insulin, amylin, incretins, and glucagon to use and control the glucose that we get from food and use for our energy needs. Insulin, in particular, plays an important role in glucose control. It serves as sort of a “gate keeper,” allowing glucose to enter cells where it can be transformed into energy and used to support vital cell functions.
What happens in type 2 diabetes is that the body loses the ability to use the insulin it produces effectively (this is called “insulin resistance”).1-3

In addition to a deficiency in insulin, abnormalities with the other hormones involved in glucose control also contribute to loss of glucose control. In addition to insulin resistance, loss of the ability to produce insulin also plays a role in elevated blood glucose. In fact, by the time that most people are diagnosed with type 2 diabetes, they have already lost over 50% of their ability to make the insulin they need. The process that leads to the development of type 2 diabetes, involving insulin resistance and loss of the ability to produce insulin, can begin well before a person is diagnosed with type 2 diabetes. In many people, insulin resistance and decreased insulin production develops over a period of 5 to 10 years before high blood sugar is detected.1-3

Causes of type 1 diabetes

In type 1 diabetes, the immune system destroys beta cells in the pancreas, the cells that produce insulin. Destruction of beta cells results from what is called an autoimmune response. A similar thing happens in other autoimmune diseases, such as rheumatoid arthritis, Crohn’s disease, and psoriasis, where the immune system mistakenly attacks the body’s healthy tissue. In fact, the word autoimmune combines the words auto, which means self, and immune to communicate the idea of the immune system attacking the body itself.

We don’t understand exactly why this autoimmune response happens. But we think that environmental factors, including exposure to pathogens (viruses), foods, and other substances, may trigger the disease in people who are already susceptible (people who have certain susceptible genes). Type 1 diabetes is often diagnosed in childhood, but can occur at any age. Destruction of beta cells occurs gradually over many months or years. During the initial stages as the disease develops, a person may experience no symptoms. In fact, common symptoms associated with high blood sugar, such as thirst and frequent urination, will not typically occur until 90% of beta cells have been destroyed.6

While type 1 diabetes can occur in a person with a family history of the disease, it can also develop where there is no such family history. However, a person with a close relative (a child or sibling) with type 1 diabetes has a greater chance of the developing the disease than someone without such a close family history (a 5% to 6% risk compared with a less than 1% risk). Researchers have identified several genes that increase susceptibility for developing type 1 diabetes. Included among these are genes involved in beta cell function (insulin production) and immune system function. Having one or more of these genes means that you are at increased risk for the disease.6.7

Most research now is focused on discovering the environmental triggers that work in genetically susceptible individuals to result in development of type 1 diabetes.

Causes of type 2 diabetes

Like type 1 diabetes, type 2 diabetes is thought to result from a combination of genetic and environmental factors. However, with type 2 diabetes the influence of genes (family heredity) on the risk of developing the disease appears to be stronger.

A much greater percentage of people who develop type 2 diabetes (compared to those who develop type 1 diabetes) have a close family member (parent, sibling, or child) who has type 2 diabetes or a medical condition associated with diabetes, such as obesity, elevated cholesterol, or high blood pressure. In fact, a person with a first-degree relative (parent, sibling, or child) with type 2 diabetes is 5 to 10 times more likely to develop the disease than someone without such as close family history. Additionally, the risk for developing type 2 diabetes is highest among certain ethnic groups (people of Hispanic, African, or Asian descent).8

Even though genetic inheritance plays a significant role in the development of type 2 diabetes, environmental factors (including pattern of eating, physical activity, smoking) also play a crucial role. In fact, type 2 diabetes is often called a disease of “lifestyle”, which means that lifestyle choices determine your risk for developing the disease. This is good news for you if you are at risk for type 2 diabetes and even if you have type 2 diabetes, because it gives you a set of important tools that you can use to help you prevent or control the disease.

Learn more about the role of heredity in causing diabetes.

Learn more about the role of environmental and lifestyle factors in causing diabetes.

Written by: Jonathan Simmons | Last reviewed: May 2014.
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